fix: test_stretch_reduces_duration — remove stale self param, fix mock data size, fix atempo assertion

- __post_init__: _apply_none_defaults() iterates dataclasses.fields() dynamically
- _NUMERIC_CONSTRAINTS and _ENUM_CONSTRAINTS dicts replace per-field if chains
- Both adapters pass values as-is (no 'or default' fallbacks)
- 18 validation tests + updated adapter tests for Enum assertions

.gitignore

@@ -39,3 +39,4 @@ dist/
 test_assets/
 dev_notes/
 .claude/
+.coverage

abogen/application/__init__.py

@@ -0,0 +1,8 @@
+"""Application layer for conversion flow unification.
+
+This package contains the application-level orchestration logic
+that bridges UI adapters (PyQt, WebUI) with domain functions.
+
+The main entry point is ConversionService.run() which coordinates
+planning, execution, and finalization of a conversion job.
+"""

abogen/application/conversion_executor.py

@@ -0,0 +1,434 @@
+"""Unified conversion executor.
+
+Takes a ConversionPlan and ports, executes the TTS conversion,
+and returns a ConversionResult. No UI imports allowed.
+
+This is Stage 6 of the conversion flow unification plan.
+"""
+
+from __future__ import annotations
+
+import time
+from contextlib import ExitStack
+from typing import Any, Callable, Dict, List, Optional, Tuple
+
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    SegmentPlan,
+)
+from abogen.application.conversion_ports import (
+    AudioSink,
+    ConversionEvents,
+    PipelineProvider,
+    SubtitleWriter,
+    VoiceResolver,
+)
+from abogen.application.conversion_result import ConversionResult
+from abogen.domain.audio_sink import open_audio_sink
+from abogen.domain.conversion_engine import (
+    SegmentStats,
+    SynthParams,
+    process_and_write_subtitles,
+    synthesize_text,
+)
+from abogen.domain.enums import OutputFormat, SubtitleMode
+from abogen.domain.normalization import TTSContext
+from abogen.domain.output_paths import sanitize_filename_for_chapter
+from abogen.infrastructure.subtitle_writer import make_subtitle_writer
+
+
+def execute_conversion(
+    plan: ConversionPlan,
+    events: ConversionEvents,
+    pipeline_provider: PipelineProvider,
+    voice_resolver: VoiceResolver,
+    tts_context: TTSContext,
+    *,
+    check_cancelled: Optional[Callable[[], None]] = None,
+) -> ConversionResult:
+    """Execute a conversion plan and return the result.
+
+    Args:
+        plan: The conversion plan from build_conversion_plan()
+        events: UI-specific callbacks (log, progress, check_cancelled)
+        pipeline_provider: Provides TTS backends
+        voice_resolver: Resolves voice specs into loaded voices
+        tts_context: Normalization context for text processing
+        check_cancelled: Optional cancellation checker (overrides events.check_cancelled)
+
+    Returns:
+        ConversionResult with paths and markers
+
+    Raises:
+        ConversionCancelled: If conversion is cancelled
+    """
+    request = plan.request
+    result = ConversionResult(metadata=plan.metadata)
+
+    # Determine cancellation checker
+    if check_cancelled is None:
+        check_cancelled = lambda: events.check_cancelled()
+
+    # Stats for progress tracking
+    total_characters = sum(
+        len(ch.body_text) for ch in plan.chapters
+    )
+    if plan.intro and plan.intro.enabled:
+        total_characters += len(plan.intro.text)
+    if plan.outro and plan.outro.enabled:
+        total_characters += len(plan.outro.text)
+
+    stats = SegmentStats(
+        processed_chars=0,
+        current_time=0.0,
+        etr_start_time=time.time(),
+        total_characters=total_characters,
+    )
+
+    # Compute subtitle flag once (used in every synthesize_text call)
+    use_spacy = request.subtitle_mode not in (SubtitleMode.DISABLED, SubtitleMode.LINE)
+
+    # Output paths
+    output_layout = plan.output_layout
+    if not output_layout:
+        raise ValueError("ConversionPlan must have an output_layout")
+
+    # Determine if merged output is needed
+    merge_chapters = request.merge_chapters_at_end or not request.save_chapters_separately
+    if request.output_format == OutputFormat.M4B:
+        merge_chapters = True
+
+    # Resolve voices
+    base_voice_spec = request.voice or "M1"
+    base_provider, base_voice_choice, base_speed, base_steps = _resolve_voice(
+        voice_resolver, base_voice_spec, request
+    )
+
+    # Use ExitStack for resource management
+    with ExitStack() as stack:
+        # Open merged audio sink
+        audio_sink: Optional[AudioSink] = None
+        audio_path = None
+        if merge_chapters:
+            audio_path = output_layout.audio_dir / f"{_base_name(request)}.{request.output_format}"
+            meta = plan.metadata if plan.metadata else None
+            audio_sink = stack.enter_context(
+                open_audio_sink(
+                    audio_path,
+                    request.output_format,
+                    metadata=meta,
+                    cancel_check=check_cancelled,
+                )
+            )
+            result.audio_path = audio_path
+
+        # Open subtitle writer if needed
+        subtitle_writer: Optional[SubtitleWriter] = None
+        if request.subtitle_mode != SubtitleMode.DISABLED and audio_sink:
+            subtitle_writer = make_subtitle_writer(
+                audio_path,
+                request.subtitle_format,
+                request.subtitle_mode,
+                max_words=request.max_subtitle_words,
+            )
+            if subtitle_writer:
+                subtitle_writer.open()
+                stack.callback(subtitle_writer.close)
+                result.subtitle_paths.append(subtitle_writer.path)
+
+        effective_subtitle_mode = request.subtitle_mode if subtitle_writer else SubtitleMode.DISABLED
+
+        synth = SynthParams(
+            tts_context=tts_context,
+            stats=stats,
+            check_cancel=check_cancelled,
+            on_progress=lambda pct, etr: events.progress(pct, etr),
+            audio_sink=audio_sink,
+            subtitle_mode=effective_subtitle_mode,
+            max_subtitle_words=request.max_subtitle_words,
+            lang_code=request.language,
+            use_spacy_segmentation=use_spacy,
+        )
+
+        # Chapter directory
+        chapter_dir = None
+        if request.save_chapters_separately and len(plan.chapters) > 1:
+            chapter_dir = output_layout.audio_dir / "chapters"
+            chapter_dir.mkdir(parents=True, exist_ok=True)
+
+        # Process intro
+        intro_emitted = False
+        if plan.intro and plan.intro.enabled and merge_chapters:
+            events.log(f"Title intro: {plan.intro.text[:80]}")
+            intro_provider, intro_voice, intro_speed, intro_steps = _resolve_voice(
+                voice_resolver, plan.intro.voice_spec, request
+            )
+            intro_backend = pipeline_provider.get(intro_provider, request.language, request.use_gpu)
+            synthesize_text(
+                text=plan.intro.text,
+                params=synth,
+                backend=intro_backend,
+                voice=intro_voice,
+                speed=intro_speed or request.speed,
+                chapter_sink=None,
+                preview_callback=lambda text: events.log(f"  {text[:80]}"),
+            )
+            intro_emitted = True
+            events.log("Intro synthesized.")
+
+        # Chapter loop
+        for chapter_idx, chapter in enumerate(plan.chapters, 1):
+            check_cancelled()
+
+            chapter_display = f"Chapter {chapter_idx}/{len(plan.chapters)}: {chapter.title}"
+            events.log(f"Processing {chapter_display}")
+
+            # Resolve chapter voice
+            chapter_provider, chapter_voice, chapter_speed, chapter_steps = _resolve_voice(
+                voice_resolver, chapter.voice_spec, request
+            )
+            chapter_backend = pipeline_provider.get(chapter_provider, request.language, request.use_gpu)
+
+            # Per-chapter sink
+            chapter_sink: Optional[AudioSink] = None
+            chapter_path = None
+            if chapter_dir:
+                chapter_filename = sanitize_filename_for_chapter(chapter.title, chapter_idx)
+                chapter_path = chapter_dir / f"{chapter_filename}.{request.separate_chapters_format}"
+                chapter_sink = stack.enter_context(
+                    open_audio_sink(
+                        chapter_path,
+                        request.separate_chapters_format,
+                        cancel_check=check_cancelled,
+                    )
+                )
+                result.chapter_paths.append(chapter_path)
+
+            # Intro delay before first chapter
+            if not intro_emitted and plan.intro and plan.intro.enabled:
+                # Intro will be emitted with first chapter
+                intro_provider, intro_voice, intro_speed, intro_steps = _resolve_voice(
+                    voice_resolver, plan.intro.voice_spec, request
+                )
+                intro_backend = pipeline_provider.get(intro_provider, request.language, request.use_gpu)
+                synthesize_text(
+                    text=plan.intro.text,
+                    params=synth,
+                    backend=intro_backend,
+                    voice=intro_voice,
+                    speed=intro_speed or request.speed,
+                    chapter_sink=chapter_sink,
+                    preview_callback=lambda text: events.log(f"  Intro: {text[:80]}"),
+                )
+                intro_emitted = True
+                if request.chapter_intro_delay > 0:
+                    _append_silence(
+                        request.chapter_intro_delay,
+                        chapter_sink=chapter_sink,
+                        audio_sink=audio_sink,
+                        stats=stats,
+                    )
+
+            # Process heading
+            if chapter.title:
+                heading_text = _format_heading(chapter.title, chapter_idx, request)
+                if heading_text:
+                    synthesize_text(
+                        text=heading_text,
+                        params=synth,
+                        backend=chapter_backend,
+                        voice=chapter_voice,
+                        speed=chapter_speed or request.speed,
+                        chapter_sink=chapter_sink,
+                        preview_callback=lambda text: events.log(f"  Title: {text[:80]}"),
+                    )
+                    if request.chapter_intro_delay > 0:
+                        _append_silence(
+                            request.chapter_intro_delay,
+                            chapter_sink=chapter_sink,
+                            audio_sink=audio_sink,
+                            stats=stats,
+                        )
+
+            # Process body segments
+            chapter_chunk_markers: List[Dict[str, Any]] = []
+            for seg_idx, segment in enumerate(chapter.segments):
+                check_cancelled()
+
+                # Resolve segment voice (may differ from chapter voice)
+                if segment.voice_spec != chapter.voice_spec:
+                    seg_provider, seg_voice, seg_speed, seg_steps = _resolve_voice(
+                        voice_resolver, segment.voice_spec, request
+                    )
+                    seg_backend = pipeline_provider.get(seg_provider, request.language, request.use_gpu)
+                else:
+                    seg_provider = chapter_provider
+                    seg_voice = chapter_voice
+                    seg_speed = chapter_speed
+                    seg_backend = chapter_backend
+
+                seg_start_time = stats.current_time
+                local_segments, accumulated_tokens = synthesize_text(
+                    text=segment.text,
+                    params=synth,
+                    backend=seg_backend,
+                    voice=seg_voice,
+                    speed=seg_speed or request.speed,
+                    chapter_sink=chapter_sink,
+                    preview_callback=lambda text: events.log(f"  {text[:80]}"),
+                )
+
+                # Process subtitles
+                if subtitle_writer and audio_sink and accumulated_tokens:
+                    process_and_write_subtitles(
+                        accumulated_tokens,
+                        subtitle_writer,
+                        subtitle_mode=request.subtitle_mode,
+                        max_subtitle_words=request.max_subtitle_words,
+                        lang_code=request.language,
+                        use_spacy_segmentation=use_spacy,
+                        fallback_end_time=stats.current_time,
+                    )
+
+                # Record chunk marker
+                if segment.source in ("chunk", "voice_marker"):
+                    chapter_chunk_markers.append({
+                        "id": segment.chunk_id,
+                        "chapter_index": chapter_idx - 1,
+                        "chunk_index": segment.chunk_index or seg_idx,
+                        "start": seg_start_time,
+                        "end": stats.current_time,
+                        "speaker_id": segment.speaker_id,
+                        "voice": segment.voice_spec,
+                        "level": segment.level or request.chunk_level,
+                        "characters": len(segment.text),
+                    })
+
+            # Silence between chapters
+            if chapter_idx < len(plan.chapters) and request.silence_between_chapters > 0:
+                _append_silence(
+                    request.silence_between_chapters,
+                    chapter_sink=chapter_sink,
+                    audio_sink=audio_sink,
+                    stats=stats,
+                )
+
+            # Close chapter sink
+            if chapter_sink:
+                chapter_sink.close()
+
+            # Add chapter marker
+            result.chapter_markers.append({
+                "chapter_index": chapter_idx - 1,
+                "title": chapter.title,
+                "start": stats.current_time - (stats.current_time - seg_start_time) if chapter.segments else stats.current_time,
+                "end": stats.current_time,
+            })
+
+            result.chunk_markers.extend(chapter_chunk_markers)
+
+        # Process outro
+        if plan.outro and plan.outro.enabled and merge_chapters:
+            events.log(f"Closing outro: {plan.outro.text[:80]}")
+            outro_provider, outro_voice, outro_speed, outro_steps = _resolve_voice(
+                voice_resolver, plan.outro.voice_spec, request
+            )
+            outro_backend = pipeline_provider.get(outro_provider, request.language, request.use_gpu)
+
+            # Silence before outro
+            if request.silence_between_chapters > 0:
+                _append_silence(
+                    request.silence_between_chapters,
+                    chapter_sink=None,
+                    audio_sink=audio_sink,
+                    stats=stats,
+                )
+
+            synthesize_text(
+                text=plan.outro.text,
+                params=synth,
+                backend=outro_backend,
+                voice=outro_voice,
+                speed=outro_speed or request.speed,
+                chapter_sink=None,
+                preview_callback=lambda text: events.log(f"  {text[:80]}"),
+            )
+            events.log("Outro synthesized.")
+
+    # Set result metadata
+    result.total_chapters = len(plan.chapters)
+    result.total_segments = sum(len(ch.segments) for ch in plan.chapters)
+    result.total_characters = total_characters
+
+    if output_layout.project_root:
+        result.project_root = output_layout.project_root
+
+    return result
+
+
+# ─── Helpers ────────────────────────────────────────────────────────
+
+
+def _resolve_voice(
+    resolver: VoiceResolver,
+    voice_spec: str,
+    request: Any,
+) -> Tuple[str, Any, Optional[float], Optional[int]]:
+    """Resolve a voice spec and return (provider, voice, speed, steps)."""
+    try:
+        resolved = resolver.resolve(voice_spec)
+        return (
+            resolved.provider,
+            resolved.voice,
+            resolved.speed,
+            resolved.supertonic_steps,
+        )
+    except Exception:
+        # Fallback to base voice
+        resolved = resolver.resolve(request.voice or "M1")
+        return (
+            resolved.provider,
+            resolved.voice,
+            resolved.speed,
+            resolved.supertonic_steps,
+        )
+
+
+def _base_name(request: Any) -> str:
+    """Get base name for output file."""
+    from abogen.domain.output_paths import sanitize_output_stem
+
+    if request.original_filename:
+        return sanitize_output_stem(request.original_filename)
+    return "output"
+
+
+def _format_heading(title: str, index: int, request: Any) -> str:
+    """Format chapter heading for TTS."""
+    from abogen.domain.chapter_titles import format_spoken_chapter_title
+
+    if request.auto_prefix_chapter_titles:
+        return format_spoken_chapter_title(title, index, apply_prefix=True)
+    return title
+
+
+def _append_silence(
+    duration: float,
+    *,
+    chapter_sink: Optional[AudioSink],
+    audio_sink: Optional[AudioSink],
+    stats: SegmentStats,
+) -> None:
+    """Append silence to sinks."""
+    from abogen.domain.audio_buffer import create_silence
+
+    silence = create_silence(duration)
+    if silence.size == 0:
+        return
+    if chapter_sink:
+        chapter_sink.write(silence)
+    if audio_sink:
+        audio_sink.write(silence)
+        stats.current_time += duration

abogen/application/conversion_models.py

@@ -0,0 +1,95 @@
+"""Core models for conversion planning.
+
+These dataclasses represent the structured plan for a conversion job.
+They are UI-agnostic and describe WHAT to convert, not HOW to do it.
+
+The planning flow:
+    ConversionRequest -> ConversionPlan -> ConversionResult
+
+    ConversionPlan contains:
+    - ChapterPlan[]: chapters with their segments
+    - SegmentPlan[]: individual text segments with voice specs
+    - OutputLayout: where to write outputs
+    - IntroOutroSpec: optional intro/outro
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import TYPE_CHECKING, Any, Dict, List, Optional
+
+if TYPE_CHECKING:
+    from abogen.application.conversion_request import ConversionRequest
+
+
+@dataclass
+class SegmentPlan:
+    """A single text segment with its voice specification.
+
+    This is the unified model for:
+    - Regular chapter body text
+    - PyQt voice markers (<<VOICE:F1>>)
+    - WebUI chunks with per-chunk voice/speaker
+    - Intro/outro text
+    - Chapter headings
+    """
+
+    text: str
+    voice_spec: str
+    kind: str = "body"  # intro, heading, body, outro
+    speaker_id: str = "narrator"
+    chunk_id: Optional[str] = None
+    chunk_index: Optional[int] = None
+    level: Optional[str] = None  # chunk level (paragraph, sentence, etc.)
+    source: str = "chapter"  # chapter, voice_marker, chunk
+
+
+@dataclass
+class ChapterPlan:
+    """A chapter with its metadata and segments."""
+
+    index: int
+    title: str
+    original_title: str
+    body_text: str
+    segments: List[SegmentPlan]
+    voice_spec: str  # default voice for this chapter
+
+
+@dataclass
+class OutputLayout:
+    """Resolved output paths for a conversion job."""
+
+    parent_dir: Path
+    merged_path: Optional[Path] = None
+    chapter_dir: Optional[Path] = None
+    project_root: Optional[Path] = None
+    audio_dir: Optional[Path] = None
+    subtitle_dir: Optional[Path] = None
+    metadata_dir: Optional[Path] = None
+
+
+@dataclass
+class IntroOutroSpec:
+    """Intro/outro specification with resolved text and voice."""
+
+    enabled: bool = False
+    text: str = ""
+    voice_spec: str = ""
+    kind: str = "intro"  # intro or outro
+
+
+@dataclass
+class ConversionPlan:
+    """Complete plan for a conversion job.
+
+    This is the output of the planning phase and input to the executor.
+    """
+
+    request: ConversionRequest
+    metadata: Dict[str, Any]
+    chapters: List[ChapterPlan]
+    intro: Optional[IntroOutroSpec] = None
+    outro: Optional[IntroOutroSpec] = None
+    output_layout: Optional[OutputLayout] = None

abogen/application/conversion_planner.py

@@ -0,0 +1,348 @@
+"""Unified conversion planner.
+
+Pure functions that take a ConversionRequest and produce a ConversionPlan.
+No side effects, no I/O — all complexity from both UIs in one place.
+
+This is Stage 2 of the conversion flow unification plan.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Dict, List, Optional, Tuple
+
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    OutputLayout,
+    SegmentPlan,
+)
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.output_layout_service import resolve_output_layout
+from abogen.domain.chapter_overrides import apply_chapter_overrides
+from abogen.domain.file_type import auto_select_relevant_chapters
+from abogen.domain.intro_outro import resolve_intro, resolve_outro
+from abogen.domain.metadata_extraction import extract_metadata_for_file
+from abogen.domain.metadata_merge import merge_metadata
+from abogen.subtitle_utils import split_text_by_voice_markers
+
+
+def build_conversion_plan(request: ConversionRequest) -> ConversionPlan:
+    """Build a complete conversion plan from a request.
+
+    This is the single entry point that both UIs will call.
+    It handles all the planning logic that was previously duplicated
+    in both PyQt and WebUI conversion runners.
+
+    Args:
+        request: Normalized conversion request
+
+    Returns:
+        ConversionPlan with all chapters, segments, and output layout
+
+    Raises:
+        ValueError: If request is invalid (no source, no chapters, etc.)
+    """
+    # 1. Extract and validate source
+    source_text = _extract_source_text(request)
+    if not source_text or not source_text.strip():
+        raise ValueError("No text content to convert")
+
+    # 2. Extract metadata
+    metadata = _extract_metadata(request)
+
+    # 3. Parse chapters
+    raw_chapters = _parse_chapters(source_text, request)
+
+    # 4. Apply chapter selection/overrides
+    selected_chapters = _apply_selection(raw_chapters, request)
+
+    # 5. Build segments for each chapter
+    chapters = _build_chapters(selected_chapters, request)
+
+    # 6. Build intro/outro
+    intro, outro = _build_intro_outro(metadata, request)
+
+    # 7. Resolve output layout
+    output_layout = resolve_output_layout(request)
+
+    return ConversionPlan(
+        request=request,
+        metadata=metadata,
+        chapters=chapters,
+        intro=intro,
+        outro=outro,
+        output_layout=output_layout,
+    )
+
+
+def _extract_source_text(request: ConversionRequest) -> Optional[str]:
+    """Extract text from request source."""
+    from abogen.subtitle_utils import clean_text
+
+    if request.direct_text:
+        return clean_text(request.direct_text)
+    if request.source_path and request.source_path.exists():
+        encoding = "utf-8"
+        try:
+            with open(request.source_path, "r", encoding=encoding, errors="replace") as f:
+                text = f.read()
+        except Exception:
+            return None
+        return clean_text(text)
+    return None
+
+
+def _extract_metadata(request: ConversionRequest) -> Dict[str, Any]:
+    """Extract metadata from source file."""
+    if request.direct_text:
+        return dict(request.metadata_tags)
+
+    if request.source_path and request.source_path.exists():
+        try:
+            extraction = extract_metadata_for_file(
+                str(request.source_path), is_direct_text=False
+            )
+            metadata = dict(extraction.metadata) if extraction.metadata else {}
+        except Exception:
+            metadata = {}
+        metadata = merge_metadata(metadata, request.metadata_tags)
+        return metadata
+
+    return dict(request.metadata_tags)
+
+
+def _parse_chapters(
+    source_text: str, request: ConversionRequest
+) -> List[Tuple[str, str, str]]:
+    """Parse source text into raw chapters.
+
+    Returns list of (title, body_text, default_voice) tuples.
+    """
+    from abogen.domain.text_chapters import parse_chapters_from_text
+
+    # Text is already cleaned in _extract_source_text, so clean=False here
+    chapters = parse_chapters_from_text(source_text, default_title="text", clean=False)
+
+    # Default voice from request
+    default_voice = request.voice or "M1"
+
+    return [(title, text, default_voice) for title, text in chapters]
+
+
+def _apply_selection(
+    raw_chapters: List[Tuple[str, str, str]], request: ConversionRequest
+) -> List[Tuple[str, str, str]]:
+    """Apply chapter selection and overrides."""
+    from abogen.text_extractor import ExtractedChapter
+
+    # Convert to ExtractedChapter objects for auto_select_relevant_chapters
+    extracted = [
+        ExtractedChapter(title=title, text=text)
+        for title, text, _ in raw_chapters
+    ]
+
+    # If user specified chapters, apply overrides
+    if request.chapter_overrides:
+        selected, _, diagnostics = apply_chapter_overrides(extracted, request.chapter_overrides)
+        if selected:
+            # Map back to (title, text, voice) tuples
+            result = []
+            for ch in selected:
+                # Find matching original chapter to get voice
+                voice = request.voice or "M1"
+                for orig_title, orig_text, orig_voice in raw_chapters:
+                    if orig_title == ch.title:
+                        voice = orig_voice
+                        break
+                result.append((ch.title, ch.text or "", voice))
+            return result
+        # If no chapters selected, fall through to auto-selection
+
+    # Auto-select relevant chapters
+    from abogen.domain.file_type import infer_file_type
+
+    file_type = infer_file_type(request.source_path) if request.source_path else "text"
+    result = auto_select_relevant_chapters(extracted, file_type)
+    filtered = result.kept
+
+    if filtered:
+        # Map back to (title, text, voice) tuples
+        result = []
+        for ch in filtered:
+            voice = request.voice or "M1"
+            for orig_title, orig_text, orig_voice in raw_chapters:
+                if orig_title == ch.title:
+                    voice = orig_voice
+                    break
+            result.append((ch.title, ch.text or "", voice))
+        return result
+
+    # Fall back to all chapters
+    return raw_chapters
+
+
+def _build_chapters(
+    selected_chapters: List[Tuple[str, str, str]], request: ConversionRequest
+) -> List[ChapterPlan]:
+    """Build ChapterPlan with SegmentPlan for each chapter."""
+    chapters = []
+
+    for idx, (title, body_text, default_voice) in enumerate(selected_chapters, 1):
+        # Build segments for this chapter
+        segments = _build_segments(body_text, default_voice, request)
+
+        chapter = ChapterPlan(
+            index=idx,
+            title=title,
+            original_title=title,
+            body_text=body_text,
+            segments=segments,
+            voice_spec=default_voice,
+        )
+        chapters.append(chapter)
+
+    return chapters
+
+
+def _build_segments(
+    body_text: str, default_voice: str, request: ConversionRequest
+) -> List[SegmentPlan]:
+    """Build SegmentPlan list for a chapter's body text.
+
+    Handles voice markers (PyQt) and chunks (WebUI).
+    """
+    segments = []
+
+    # Check for chunks (WebUI style)
+    if request.chunks:
+        # Group chunks by chapter (simplified — assume chunks are for current chapter)
+        for chunk_idx, chunk in enumerate(request.chunks):
+            chunk_text = chunk.get("normalized_text") or chunk.get("text", "")
+            if not chunk_text or not chunk_text.strip():
+                continue
+
+            chunk_voice = _resolve_chunk_voice(chunk, default_voice, request)
+            speaker_id = chunk.get("speaker_id", "narrator")
+
+            segments.append(
+                SegmentPlan(
+                    text=chunk_text.strip(),
+                    voice_spec=chunk_voice,
+                    kind="body",
+                    speaker_id=speaker_id,
+                    chunk_id=chunk.get("id"),
+                    chunk_index=chunk.get("chunk_index", chunk_idx),
+                    level=chunk.get("level", request.chunk_level),
+                    source="chunk",
+                )
+            )
+        return segments
+
+    # Check for voice markers (PyQt style)
+    # Detect markers even if validation fails (voice names may not be loaded yet)
+    from abogen.subtitle_utils import _VOICE_MARKER_SEARCH_PATTERN
+
+    has_voice_markers = bool(_VOICE_MARKER_SEARCH_PATTERN.search(body_text))
+    voice_segments, last_voice, valid_count, invalid_count = split_text_by_voice_markers(
+        body_text, default_voice
+    )
+
+    if has_voice_markers or (len(voice_segments) > 1):
+        # Voice markers were used
+        for voice_name, segment_text in voice_segments:
+            if not segment_text or not segment_text.strip():
+                continue
+            segments.append(
+                SegmentPlan(
+                    text=segment_text.strip(),
+                    voice_spec=voice_name,
+                    kind="body",
+                    source="voice_marker",
+                )
+            )
+        return segments
+
+    # No voice markers — single segment for entire body
+    if body_text and body_text.strip():
+        segments.append(
+            SegmentPlan(
+                text=body_text.strip(),
+                voice_spec=default_voice,
+                kind="body",
+                source="chapter",
+            )
+        )
+
+    return segments
+
+
+def _resolve_chunk_voice(
+    chunk: Dict[str, Any], default_voice: str, request: ConversionRequest
+) -> str:
+    """Resolve voice for a chunk."""
+    # Check for speaker-based voice
+    speaker_id = chunk.get("speaker_id", "narrator")
+    if speaker_id and speaker_id != "narrator" and request.speakers:
+        speaker_config = request.speakers.get(speaker_id, {})
+        if isinstance(speaker_config, dict):
+            voice = speaker_config.get("voice")
+            if voice:
+                return voice
+
+    # Check for direct voice field
+    voice = chunk.get("voice")
+    if voice:
+        return voice
+
+    return default_voice
+
+
+def _build_intro_outro(
+    metadata: Dict[str, Any], request: ConversionRequest
+) -> Tuple[Optional[IntroOutroSpec], Optional[IntroOutroSpec]]:
+    """Build intro and outro specs."""
+    intro_spec = None
+    outro_spec = None
+
+    # Intro
+    if request.read_title_intro:
+        resolved = resolve_intro(
+            metadata,
+            request.original_filename,
+            True,
+            request.voice or "M1",
+            request.voice or "M1",
+            [],
+        )
+        if resolved.enabled:
+            intro_spec = IntroOutroSpec(
+                enabled=True,
+                text=resolved.text,
+                voice_spec=resolved.voice_spec,
+                kind="intro",
+            )
+
+    # Outro
+    if request.read_closing_outro:
+        resolved = resolve_outro(
+            metadata,
+            request.original_filename,
+            True,
+            request.voice or "M1",
+            request.voice or "M1",
+            [],
+        )
+        if resolved.enabled:
+            outro_spec = IntroOutroSpec(
+                enabled=True,
+                text=resolved.text,
+                voice_spec=resolved.voice_spec,
+                kind="outro",
+            )
+
+    return intro_spec, outro_spec
+
+
+# Output layout resolution is now in application/output_layout_service.py

abogen/application/conversion_ports.py

@@ -0,0 +1,112 @@
+"""Ports / interfaces for the conversion service.
+
+These protocols define how the conversion service communicates with
+the outside world (UI, TTS backends, voice resolvers).
+
+The service ONLY depends on these interfaces, never on concrete
+implementations (PyQt signals, Flask Job, etc.).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, List, Optional, Protocol, runtime_checkable
+
+
+class ConversionCancelled(Exception):
+    """Raised when conversion is cancelled by user."""
+    pass
+
+
+class ConversionEvents(Protocol):
+    """UI-specific actions the conversion service delegates back to the caller.
+
+    Implementations:
+    - PyQt: emits signals (log_updated, progress_updated, etc.)
+    - WebUI: updates Job attributes (job.add_log, job.progress, etc.)
+    """
+
+    def log(self, message: str, level: str = "info") -> None:
+        """Log a message to the UI."""
+        ...
+
+    def progress(self, processed: int, total: int, etr: str) -> None:
+        """Update progress display."""
+        ...
+
+    def check_cancelled(self) -> None:
+        """Check if conversion was cancelled.
+
+        Should raise ConversionCancelled (or UI-specific exception)
+        if cancellation is requested. Normal return means "continue".
+        """
+        ...
+
+
+class PipelineProvider(Protocol):
+    """Provides access to TTS backends (Kokoro, SuperTonic, etc.).
+
+    Implementations:
+    - PyQt: wraps self.backend (single pipeline)
+    - WebUI: wraps PipelinePool (multi-provider)
+    """
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> Any:
+        """Get a TTS backend instance."""
+        ...
+
+    def dispose_all(self) -> None:
+        """Dispose all backend resources."""
+        ...
+
+
+@dataclass
+class ResolvedVoice:
+    """A resolved voice ready for TTS synthesis."""
+
+    provider: str
+    resolved_spec: str
+    voice: Any  # loaded voice tensor or name
+    speed: float
+    supertonic_steps: int
+
+
+class VoiceResolver(Protocol):
+    """Resolves voice specs into loaded voice objects.
+
+    Implementations:
+    - PyQt: wraps load_voice_cached + VoiceCache
+    - WebUI: wraps resolve_voice_choice + PipelinePool + VoiceCache
+    """
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        ...
+
+
+class SubtitleWriter(Protocol):
+    """Writes subtitle entries to a file."""
+
+    def open(self) -> None:
+        """Open the subtitle file for writing."""
+        ...
+
+    def write_entry(self, start: float, end: float, text: str) -> None:
+        """Write a single subtitle entry."""
+        ...
+
+    def close(self) -> None:
+        """Close the subtitle file."""
+        ...
+
+
+class AudioSink(Protocol):
+    """Writes audio data to a file."""
+
+    def write(self, audio: Any) -> None:
+        """Write audio samples to the sink."""
+        ...
+
+    def close(self) -> None:
+        """Close the audio file."""
+        ...

abogen/application/conversion_request.py

@@ -0,0 +1,156 @@
+"""ConversionRequest — normalized input for a conversion job.
+
+This is NOT a WebUI Job and NOT a PyQt ConversionThread state.
+It describes the TASK, not the UI.
+
+UI adapters are responsible for converting their respective state
+into a ConversionRequest before calling ConversionService.run().
+"""
+
+from __future__ import annotations
+
+import dataclasses
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+from abogen.domain.enums import Language, OutputFormat, SaveMode, SubtitleFormat, SubtitleMode
+
+
+class ConversionRequestError(ValueError):
+    """Raised when ConversionRequest has invalid field values."""
+
+
+# Numeric field constraints: attr -> (min, max)
+_NUMERIC_CONSTRAINTS: dict[str, tuple[float, float | None]] = {
+    "max_subtitle_words": (1, 500),
+    "speed": (0.5, 3.0),
+    "supertonic_total_steps": (2, 15),
+    "silence_between_chapters": (0.0, None),
+    "chapter_intro_delay": (0.0, None),
+}
+
+# Enum-like fields that must be in allowed set
+_ENUM_CONSTRAINTS: dict[str, tuple[str, ...]] = {
+    "chunk_level": ("paragraph", "sentence"),
+    "speaker_mode": ("single", "multi"),
+}
+
+
+@dataclass
+class ConversionRequest:
+    """Normalized request for a conversion job.
+
+    Only contains fields that describe the conversion task itself.
+    UI-only fields (display, logging, user prompts) stay in adapters.
+
+    Validation runs on creation via __post_init__:
+    - None values → replaced with field default (from declaration)
+    - Numeric fields → clamped to valid range
+    - String enums → validated against allowed set
+    """
+
+    # --- Source ---
+    source_path: Optional[Path] = None
+    direct_text: Optional[str] = None
+    original_filename: str = ""
+
+    # --- TTS Settings ---
+    language: Language = Language.EN_US
+    tts_provider: str = "kokoro"
+    voice: str = "M1"
+    voice_profile: Optional[str] = None
+    speed: float = 1.0
+    use_gpu: bool = True
+    supertonic_total_steps: int = 5
+
+    # --- Output Format ---
+    output_format: OutputFormat = OutputFormat.WAV
+    subtitle_mode: SubtitleMode = SubtitleMode.DISABLED
+    subtitle_format: SubtitleFormat = SubtitleFormat.SRT
+    max_subtitle_words: int = 50
+
+    # --- Save Options ---
+    save_mode: SaveMode = SaveMode.SAVE_NEXT_TO_INPUT
+    output_folder: Optional[Path] = None
+    save_chapters_separately: bool = False
+    merge_chapters_at_end: bool = True
+    separate_chapters_format: OutputFormat = OutputFormat.WAV
+    save_as_project: bool = False
+
+    # --- Timing ---
+    silence_between_chapters: float = 2.0
+    chapter_intro_delay: float = 0.0
+
+    # --- Content Processing ---
+    replace_single_newlines: bool = False
+    read_title_intro: bool = False
+    read_closing_outro: bool = True
+    auto_prefix_chapter_titles: bool = True
+    normalize_chapter_opening_caps: bool = False
+
+    # --- Pronunciation / Normalization ---
+    pronunciation_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    manual_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    heteronym_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    normalization_overrides: Optional[Dict[str, Any]] = None
+
+    # --- Chapter/Chunk Configuration ---
+    chapter_overrides: List[Dict[str, Any]] = field(default_factory=list)
+    chunks: List[Dict[str, Any]] = field(default_factory=list)
+    chunk_level: str = "paragraph"
+    speaker_mode: str = "single"
+    speakers: Dict[str, Any] = field(default_factory=dict)
+
+    # --- Metadata ---
+    metadata_tags: Dict[str, Any] = field(default_factory=dict)
+
+    # --- Artifacts ---
+    cover_image_path: Optional[Path] = None
+    cover_image_mime: Optional[str] = None
+    generate_epub3: bool = False
+
+    def __post_init__(self) -> None:
+        """Resolve None → default, then validate and clamp."""
+        _apply_none_defaults(self)
+        if not self.tts_provider:
+            self.tts_provider = "kokoro"
+        _clamp_numerics(self)
+        _validate_enums(self)
+
+
+def _apply_none_defaults(obj: ConversionRequest) -> None:
+    """Replace None values with field defaults from dataclass declaration."""
+    for f in dataclasses.fields(obj):
+        if getattr(obj, f.name) is not None:
+            continue
+        if f.default is not dataclasses.MISSING:
+            setattr(obj, f.name, f.default)
+        elif f.default_factory is not dataclasses.MISSING:
+            setattr(obj, f.name, f.default_factory())
+
+
+def _clamp_numerics(obj: ConversionRequest) -> None:
+    """Clamp numeric fields to valid ranges."""
+    for attr, (min_v, max_v) in _NUMERIC_CONSTRAINTS.items():
+        val = getattr(obj, attr)
+        if val is None:
+            continue
+        if not isinstance(val, (int, float)):
+            raise ConversionRequestError(
+                f"{attr} must be a number, got {type(val).__name__}"
+            )
+        clamped = max(min_v, float(val))
+        if max_v is not None:
+            clamped = min(max_v, clamped)
+        setattr(obj, attr, clamped)
+
+
+def _validate_enums(obj: ConversionRequest) -> None:
+    """Validate string enum fields against allowed values."""
+    for attr, allowed in _ENUM_CONSTRAINTS.items():
+        val = getattr(obj, attr)
+        if val not in allowed:
+            raise ConversionRequestError(
+                f"{attr} must be one of {allowed}, got {val!r}"
+            )

abogen/application/conversion_result.py

@@ -0,0 +1,47 @@
+"""ConversionResult — output of a successful conversion.
+
+Returned by ConversionService.run() after all synthesis and finalization.
+UI adapters consume this to update their respective state (Job, signals, etc.).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+
+@dataclass
+class ConversionResult:
+    """Output of a successful conversion job."""
+
+    # --- Primary outputs ---
+    audio_path: Optional[Path] = None
+    subtitle_paths: List[Path] = field(default_factory=list)
+    chapter_paths: List[Path] = field(default_factory=list)
+
+    # --- Markers (for metadata/audiobookshelf) ---
+    chapter_markers: List[Dict[str, Any]] = field(default_factory=list)
+    chunk_markers: List[Dict[str, Any]] = field(default_factory=list)
+
+    # --- Metadata ---
+    metadata: Dict[str, Any] = field(default_factory=dict)
+
+    # --- Artifacts ---
+    artifacts: Dict[str, Path] = field(default_factory=dict)
+    project_root: Optional[Path] = None
+    epub_path: Optional[Path] = None
+
+    # --- Stats ---
+    total_chapters: int = 0
+    total_segments: int = 0
+    total_characters: int = 0
+
+
+@dataclass
+class ConversionError:
+    """Error information when conversion fails."""
+
+    message: str
+    details: Optional[str] = None
+    is_cancelled: bool = False

abogen/application/conversion_service.py

@@ -0,0 +1,172 @@
+"""ConversionService — main orchestrator for the conversion flow.
+
+Ties together planner, executor, and finalizers into a single entry point.
+Both UIs (PyQt, WebUI) call ConversionService.run() to execute a conversion.
+
+Responsibilities:
+- Prepare TTSContext (normalization settings, pronunciation rules)
+- Build ConversionPlan via planner
+- Execute conversion via executor
+- Handle lifecycle (cleanup, error handling)
+- Return ConversionResult
+
+The service NEVER imports from PyQt or WebUI.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Callable, Dict, Optional
+
+from abogen.application.conversion_executor import execute_conversion
+from abogen.application.conversion_models import ConversionPlan
+from abogen.application.conversion_planner import build_conversion_plan
+from abogen.application.conversion_ports import (
+    ConversionEvents,
+    PipelineProvider,
+    VoiceResolver,
+)
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_result import ConversionResult
+from abogen.domain.enums import SubtitleMode
+from abogen.domain.normalization import TTSContext
+from abogen.domain.split_pattern import get_split_pattern
+
+
+def run_conversion(
+    request: ConversionRequest,
+    events: ConversionEvents,
+    pipeline_provider: PipelineProvider,
+    voice_resolver: VoiceResolver,
+) -> ConversionResult:
+    """Execute a conversion request and return the result.
+
+    This is the single entry point for both UIs. It orchestrates:
+    1. TTS context preparation
+    2. Conversion planning
+    3. Conversion execution
+    4. Resource cleanup
+
+    Args:
+        request: Normalized conversion request
+        events: UI-specific callbacks (log, progress, check_cancelled)
+        pipeline_provider: Provides TTS backends
+        voice_resolver: Resolves voice specs into loaded voices
+
+    Returns:
+        ConversionResult with paths and markers
+
+    Raises:
+        ConversionCancelled: If conversion was cancelled
+        ValueError: If request is invalid
+        Exception: On TTS or I/O errors
+    """
+    try:
+        # Stage 1: Prepare TTS context
+        events.log("Preparing conversion pipeline")
+        tts_context = _prepare_tts_context(request, events)
+
+        # Stage 2: Build conversion plan
+        events.log("Building conversion plan")
+        plan = build_conversion_plan(request)
+
+        # Stage 3: Execute conversion
+        events.log("Starting conversion")
+        result = execute_conversion(
+            plan=plan,
+            events=events,
+            pipeline_provider=pipeline_provider,
+            voice_resolver=voice_resolver,
+            tts_context=tts_context,
+        )
+
+        # Stage 4: Finalize
+        events.log("Conversion complete")
+        return result
+
+    except Exception as e:
+        events.log(f"Conversion failed: {e}", level="error")
+        raise
+
+
+def _prepare_tts_context(
+    request: ConversionRequest,
+    events: ConversionEvents,
+) -> TTSContext:
+    """Prepare TTSContext with normalization settings.
+
+    This compiles pronunciation/heteronym rules and creates the
+    normalization context used during conversion.
+
+    Args:
+        request: Conversion request with override settings
+        events: For logging warnings about missing features
+
+    Returns:
+        TTSContext ready for text normalization
+    """
+    from abogen.domain.normalization import (
+        build_apostrophe_config,
+        get_runtime_settings,
+    )
+    from abogen.domain.pronunciation import (
+        compile_heteronym_sentence_rules,
+        compile_pronunciation_rules,
+        merge_pronunciation_overrides,
+    )
+
+    # Get runtime normalization settings
+    normalization_settings = get_runtime_settings()
+
+    # Build apostrophe config
+    apostrophe_config = build_apostrophe_config(
+        settings=normalization_settings,
+    )
+
+    # Check for num2words availability
+    if apostrophe_config.convert_numbers:
+        try:
+            import num2words  # noqa: F401
+        except ImportError:
+            events.log(
+                "Number normalization is enabled but 'num2words' library is not available. "
+                "Numbers will NOT be converted to words.",
+                level="warning",
+            )
+
+    # Compute split pattern
+    split_pattern = get_split_pattern(
+        request.language or Language.EN_US,
+        request.subtitle_mode or SubtitleMode.DISABLED,
+    )
+
+    # Merge pronunciation overrides (manual + pronunciation)
+    # Create a mock job-like object for merge_pronunciation_overrides
+    class _MockJob:
+        def __init__(self, req):
+            self.pronunciation_overrides = req.pronunciation_overrides
+            self.manual_overrides = req.manual_overrides
+            self.heteronym_overrides = req.heteronym_overrides
+
+    merged_overrides = merge_pronunciation_overrides(_MockJob(request))
+
+    # Compile rules
+    pronunciation_rules = compile_pronunciation_rules(merged_overrides)
+    heteronym_rules = compile_heteronym_sentence_rules(request.heteronym_overrides)
+
+    if heteronym_rules:
+        events.log(
+            f"Applying {len(heteronym_rules)} heteronym override(s) during conversion.",
+            level="debug",
+        )
+    if pronunciation_rules:
+        events.log(
+            f"Applying {len(pronunciation_rules)} pronunciation override(s) during conversion.",
+            level="debug",
+        )
+
+    return TTSContext(
+        split_pattern=split_pattern,
+        pronunciation_rules=pronunciation_rules,
+        heteronym_rules=heteronym_rules,
+        normalization_overrides=request.normalization_overrides,
+    )

abogen/application/output_layout_service.py

@@ -0,0 +1,150 @@
+"""Output layout resolution service.
+
+Determines where conversion outputs (audio, subtitles, metadata) should be written.
+Extracted from conversion_planner.py as a standalone service per plan Stage 5.
+
+Responsibilities:
+- Resolve base output directory from save_mode and source_path
+- Determine base filename from original_filename
+- Find unique output path to avoid overwrites
+- Resolve project layout (audio_dir, subtitle_dir, metadata_dir)
+- Force merged output for m4b format
+- Return OutputLayout dataclass
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Optional
+
+from abogen.application.conversion_models import OutputLayout
+from abogen.application.conversion_request import ConversionRequest
+from abogen.domain.enums import OutputFormat, SaveMode, SubtitleFormat
+from abogen.domain.output_paths import (
+    resolve_project_layout,
+    resolve_unique_path,
+    sanitize_output_stem,
+)
+
+
+def resolve_output_layout(request: ConversionRequest) -> OutputLayout:
+    """Resolve output paths for a conversion request.
+
+    This is the single entry point for output path resolution,
+    used by both UIs and the conversion service.
+
+    Args:
+        request: Normalized conversion request
+
+    Returns:
+        OutputLayout with resolved paths
+    """
+    # Determine base output directory
+    if request.save_mode == SaveMode.CUSTOM_FOLDER and request.output_folder:
+        parent_dir = Path(request.output_folder)
+    elif request.source_path:
+        parent_dir = request.source_path.parent
+    else:
+        parent_dir = Path.cwd()
+
+    # Determine base name
+    if request.original_filename:
+        base_name = sanitize_output_stem(request.original_filename)
+    elif request.source_path:
+        base_name = sanitize_output_stem(request.source_path.stem)
+    else:
+        base_name = "output"
+
+    # Find unique output path
+    allowed_exts = {request.output_format, SubtitleFormat.SRT, SubtitleFormat.ASS, "vtt", "mp4", OutputFormat.M4B}
+    unique_base = resolve_unique_path(
+        parent_dir, base_name, "", allowed_extensions=allowed_exts
+    )
+
+    # Resolve project layout
+    project_root = None
+    audio_dir = parent_dir
+    subtitle_dir = None
+    metadata_dir = None
+
+    if request.save_as_project:
+        project_root, audio_dir, subtitle_dir, metadata_dir = resolve_project_layout(
+            original_filename=request.original_filename,
+            save_as_project=True,
+            base_dir=parent_dir,
+        )
+
+    return OutputLayout(
+        parent_dir=parent_dir,
+        project_root=project_root,
+        audio_dir=audio_dir,
+        subtitle_dir=subtitle_dir,
+        metadata_dir=metadata_dir,
+    )
+
+
+def resolve_merged_path(
+    layout: OutputLayout,
+    request: ConversionRequest,
+) -> Path:
+    """Resolve the merged output audio file path.
+
+    Args:
+        layout: Resolved output layout
+        request: Conversion request
+
+    Returns:
+        Path to the merged output file
+    """
+    base_name = sanitize_output_stem(
+        request.original_filename or "output"
+    )
+    return layout.audio_dir / f"{base_name}.{request.output_format}"
+
+
+def resolve_chapter_path(
+    layout: OutputLayout,
+    request: ConversionRequest,
+    chapter_title: str,
+    chapter_index: int,
+) -> Path:
+    """Resolve the output path for a separate chapter file.
+
+    Args:
+        layout: Resolved output layout
+        request: Conversion request
+        chapter_title: Chapter title for filename
+        chapter_index: Chapter number (1-based)
+
+    Returns:
+        Path to the chapter output file
+    """
+    import re
+
+    slug = re.sub(r'[^\w\s-]', '', chapter_title.lower())
+    slug = re.sub(r'[\s_]+', '_', slug).strip('_')
+    if not slug:
+        slug = f"chapter_{chapter_index}"
+    filename = f"{chapter_index:02d}_{slug}.{request.separate_chapters_format}"
+    return layout.audio_dir / "chapters" / filename
+
+
+def should_merge_output(request: ConversionRequest) -> bool:
+    """Determine if merged output is required.
+
+    Rules:
+    - m4b format always forces merged output
+    - If save_chapters_separately is False, merged is required
+    - Otherwise, use merge_chapters_at_end setting
+
+    Args:
+        request: Conversion request
+
+    Returns:
+        True if merged output should be created
+    """
+    if request.output_format == OutputFormat.M4B:
+        return True
+    if not request.save_chapters_separately:
+        return True
+    return request.merge_chapters_at_end

abogen/domain/audio_sink.py

@@ -54,7 +54,7 @@ def _ensure_ffmpeg() -> None:
 
 
 def _get_ffmpeg_cache_root() -> str:
-    from abogen.infrastructure.cache import get_internal_cache_path
+    from abogen.utils import get_internal_cache_path
 
     return get_internal_cache_path("ffmpeg")
 

abogen/domain/conversion_engine.py

@@ -23,6 +23,7 @@ from typing import Any, Callable, List, Optional, Protocol
 
 from abogen.domain.audio_sink import AudioSink
 from abogen.domain.conversion_pipeline import tts_segments
+from abogen.domain.enums import SubtitleMode
 from abogen.domain.normalization import TTSContext
 from abogen.domain.progress import calc_etr_str
 from abogen.domain.subtitle_generation import process_subtitle_tokens
@@ -55,44 +56,29 @@ class SegmentInfo:
 def run_tts_segment_loop(
     *,
     text: str,
+    params: SynthParams,
     backend: Any,
     voice: Any,
     speed: float,
     split_pattern: str,
-    stats: SegmentStats,
-    check_cancel: CancelChecker,
-    on_progress: Callable[[int, str], None],
     chapter_sink: Optional[AudioSink] = None,
-    audio_sink: Optional[AudioSink] = None,
     preview_callback: Optional[Callable[[str], None]] = None,
     on_segment: Optional[Callable[[SegmentInfo], None]] = None,
-    subtitle_mode: str = "Disabled",
-    max_subtitle_words: int = 5,
-    lang_code: str = "a",
-    use_spacy_segmentation: bool = False,
 ) -> tuple[int, list]:
     """Run the core TTS segment iteration loop.
 
     Args:
         text: Normalized text to synthesize.
+        params: Common synthesis parameters (stats, callbacks, sinks, etc.).
         backend: TTS pipeline instance (Kokoro or Supertonic).
         voice: Voice name/id for the backend.
         speed: Speech speed multiplier.
         split_pattern: Regex pattern used by the TTS engine for sentence splitting.
-        stats: Running character/timing stats (mutated in place).
-        check_cancel: Called each segment; if it returns True, iteration stops.
-        on_progress: Called with (percent, etr_str) after each segment.
-        chapter_sink: Optional audio sink for the current chapter.
-        audio_sink: Optional audio sink for the merged output.
         preview_callback: Called with a short preview string per segment.
         on_segment: Called with a SegmentInfo for each segment *before*
             audio is written.  Useful for callers that need per-segment
             subtitle processing (e.g. PyQt dual-writer pattern).
             When provided, the default subtitle accumulation is skipped.
-        subtitle_mode: Subtitle mode string (e.g. "Disabled", "Sentence").
-        max_subtitle_words: Max words per subtitle entry.
-        lang_code: Language code for subtitle processing.
-        use_spacy_segmentation: Whether spaCy sentence boundaries are active.
 
     Returns:
         Tuple of (segment_count, accumulated_subtitle_tokens).
@@ -108,26 +94,26 @@ def run_tts_segment_loop(
         voice=voice,
         speed=speed,
         split_pattern=split_pattern,
-        current_time=stats.current_time,
+        current_time=params.stats.current_time,
     ):
-        if check_cancel():
+        if params.check_cancel():
             break
 
         local_segments += 1
-        stats.processed_chars += len(seg.graphemes)
+        params.stats.processed_chars += len(seg.graphemes)
 
         # Progress
-        if stats.total_characters:
+        if params.stats.total_characters:
-            percent = min(int(stats.processed_chars / stats.total_characters * 100), 99)
+            percent = min(int(params.stats.processed_chars / params.stats.total_characters * 100), 99)
         else:
-            percent = 0 if stats.processed_chars == 0 else 99
+            percent = 0 if params.stats.processed_chars == 0 else 99
 
         etr_str = calc_etr_str(
-            time.time() - stats.etr_start_time,
+            time.time() - params.stats.etr_start_time,
-            stats.processed_chars,
+            params.stats.processed_chars,
-            stats.total_characters,
+            params.stats.total_characters,
         )
-        on_progress(percent, etr_str)
+        params.on_progress(percent, etr_str)
 
         # Preview / log
         if preview_callback:
@@ -140,23 +126,23 @@ def run_tts_segment_loop(
                 audio=seg.audio,
                 tokens=list(seg.tokens) if seg.tokens else [],
                 duration=seg.duration,
-                chunk_start=getattr(seg, "chunk_start", stats.current_time),
+                chunk_start=getattr(seg, "chunk_start", params.stats.current_time),
             )
             on_segment(info)
 
         # Write audio
         if chapter_sink:
             chapter_sink.write(seg.audio)
-        if audio_sink:
+        if params.audio_sink:
-            audio_sink.write(seg.audio)
+            params.audio_sink.write(seg.audio)
 
         # Accumulate subtitle tokens (default path; skipped if on_segment handles it)
-        if not on_segment and subtitle_mode != "Disabled" and seg.tokens:
+        if not on_segment and params.subtitle_mode != SubtitleMode.DISABLED and seg.tokens:
             accumulated_tokens.extend(seg.tokens)
 
         # Update timing
-        if audio_sink:
+        if params.audio_sink:
-            stats.current_time += seg.duration
+            params.stats.current_time += seg.duration
 
     return local_segments, accumulated_tokens
 
@@ -191,24 +177,34 @@ def process_and_write_subtitles(
         subtitle_writer.write_entry(start=start, end=end, text=text)
 
 
+@dataclass(frozen=True)
+class SynthParams:
+    """Common parameters for synthesize_text calls.
+
+    Packed once by the executor to avoid repeating identical kwargs.
+    When adding new common params, change only this dataclass.
+    """
+    tts_context: TTSContext
+    stats: SegmentStats
+    check_cancel: CancelChecker
+    on_progress: Callable[[int, str], None]
+    audio_sink: Optional[AudioSink] = None
+    subtitle_mode: str = "Disabled"
+    max_subtitle_words: int = 50
+    lang_code: str = "a"
+    use_spacy_segmentation: bool = False
+
+
 def synthesize_text(
     *,
     text: str,
-    tts_context: TTSContext,
+    params: SynthParams,
     backend: Any,
     voice: Any,
     speed: float,
-    stats: SegmentStats,
-    check_cancel: CancelChecker,
-    on_progress: Callable[[int, str], None],
     chapter_sink: Optional[AudioSink] = None,
-    audio_sink: Optional[AudioSink] = None,
     preview_callback: Optional[Callable[[str], None]] = None,
     on_segment: Optional[Callable[[SegmentInfo], None]] = None,
-    subtitle_mode: str = "Disabled",
-    max_subtitle_words: int = 5,
-    lang_code: str = "a",
-    use_spacy_segmentation: bool = False,
     split_pattern_override: Optional[str] = None,
 ) -> tuple[int, list]:
     """Normalize text and run TTS — the single entry point for both UIs.
@@ -216,22 +212,15 @@ def synthesize_text(
     Combines TTSContext.normalize() + run_tts_segment_loop() into one call.
     UI-specific concerns (provider resolution, progress display) stay in the UI.
     """
-    normalized = tts_context.normalize(text)
+    normalized = params.tts_context.normalize(text)
     return run_tts_segment_loop(
         text=normalized,
+        params=params,
         backend=backend,
         voice=voice,
         speed=speed,
-        split_pattern=split_pattern_override or tts_context.split_pattern,
+        split_pattern=split_pattern_override or params.tts_context.split_pattern,
-        stats=stats,
-        check_cancel=check_cancel,
-        on_progress=on_progress,
         chapter_sink=chapter_sink,
-        audio_sink=audio_sink,
         preview_callback=preview_callback,
         on_segment=on_segment,
-        subtitle_mode=subtitle_mode,
-        max_subtitle_words=max_subtitle_words,
-        lang_code=lang_code,
-        use_spacy_segmentation=use_spacy_segmentation,
     )

abogen/domain/conversion_pipeline.py

@@ -8,6 +8,8 @@ from __future__ import annotations
 
 import logging
 from dataclasses import dataclass, field
+
+from abogen.domain.enums import SubtitleMode
 from typing import Any, Callable, Dict, Iterator, List, Optional
 
 import numpy as np
@@ -221,7 +223,7 @@ def emit_text_to_sinks(
 
     # Flush subtitle tokens
     if subtitle_writer and accumulated_tokens:
-        _use_spacy = subtitle_mode not in ("Disabled", "Line")
+        _use_spacy = subtitle_mode not in (SubtitleMode.DISABLED, SubtitleMode.LINE)
         new_entries: List[tuple] = []
         process_subtitle_tokens(
             accumulated_tokens,

abogen/domain/enums.py

@@ -0,0 +1,179 @@
+"""Domain enums — typed constants for values tied to business logic.
+
+Using Enum instead of bare strings ensures:
+- Invalid values are caught at construction time
+- IDE autocomplete and type checking work
+- Adding new values is explicit (must update Enum)
+"""
+
+from __future__ import annotations
+
+from enum import Enum
+from pathlib import Path
+
+
+class SubtitleMode(str, Enum):
+    """Subtitle generation mode."""
+    DISABLED = "Disabled"
+    LINE = "Line"
+    SENTENCE = "Sentence"
+    SENTENCE_COMMA = "Sentence + Comma"
+    SENTENCE_HIGHLIGHT = "Sentence + Highlighting"
+
+    @classmethod
+    def from_str(cls, value: str) -> SubtitleMode:
+        """Parse from user input: case-insensitive, strips whitespace."""
+        normalized = value.strip()
+        for member in cls:
+            if member.value.lower() == normalized.lower():
+                return member
+        raise ValueError(f"Invalid SubtitleMode: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class OutputFormat(str, Enum):
+    """Audio output format."""
+    WAV = "wav"
+    MP3 = "mp3"
+    FLAC = "flac"
+    OPUS = "opus"
+    M4B = "m4b"
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.wav', '.mp3', etc."""
+        return f".{self.value}"
+
+    @property
+    def is_lossless(self) -> bool:
+        """True for lossless formats."""
+        return self in (self.WAV, self.FLAC)
+
+    @classmethod
+    def from_str(cls, value: str) -> OutputFormat:
+        """Parse from user input: strips dot prefix, case-insensitive."""
+        normalized = value.strip().lstrip(".").lower()
+        for member in cls:
+            if member.value == normalized:
+                return member
+        raise ValueError(f"Invalid OutputFormat: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class SaveMode(str, Enum):
+    """Where to save the output file."""
+    SAVE_NEXT_TO_INPUT = "save_next_to_input"
+    SAVE_TO_DESKTOP = "save_to_desktop"
+    CHOOSE_OUTPUT_FOLDER = "choose_output_folder"
+    DEFAULT_OUTPUT = "default_output"
+    CUSTOM_FOLDER = "custom_folder"
+
+
+class SubtitleFormat(str, Enum):
+    """Subtitle file format."""
+    SRT = "srt"
+    ASS = "ass"
+    VTT = "vtt"
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.srt', '.ass'."""
+        return f".{self.value}"
+
+    @classmethod
+    def from_str(cls, value: str) -> SubtitleFormat:
+        """Parse from user input: strips dot prefix, case-insensitive."""
+        normalized = value.strip().lstrip(".").lower()
+        for member in cls:
+            if member.value == normalized:
+                return member
+        raise ValueError(f"Invalid SubtitleFormat: {value!r}. Valid: {[m.value for m in cls]}")
+
+
+class InputFormat(str, Enum):
+    """Input file format."""
+    EPUB = "epub"
+    PDF = "pdf"
+    TXT = "txt"
+    MD = "md"
+    SRT = "srt"
+    ASS = "ass"
+    VTT = "vtt"
+
+    @property
+    def is_book(self) -> bool:
+        """True for book/document formats (epub, pdf, txt, md)."""
+        return self in (self.EPUB, self.PDF, self.TXT, self.MD)
+
+    @property
+    def is_subtitle(self) -> bool:
+        """True for subtitle formats (srt, ass, vtt)."""
+        return self in (self.SRT, self.ASS, self.VTT)
+
+    @property
+    def dot_ext(self) -> str:
+        """File extension with dot: '.epub', '.srt', etc."""
+        return f".{self.value}"
+
+    @classmethod
+    def from_path(cls, path: Path) -> InputFormat:
+        """Detect format from file path extension."""
+        suffix = path.suffix.lower().lstrip(".")
+        if suffix == "markdown":
+            return cls.MD
+        try:
+            return cls(suffix)
+        except ValueError:
+            raise ValueError(f"Unsupported input format: {path.suffix!r}. Supported: {[m.value for m in cls]}")
+
+
+class Language(str, Enum):
+    """TTS language code (ISO 639-1 with region where needed).
+
+    Each engine (Kokoro, Supertonic) maps these to its own
+    internal language identifiers.
+    """
+    EN_US = "en-US"
+    EN_GB = "en-GB"
+    ES = "es"
+    FR = "fr"
+    HI = "hi"
+    IT = "it"
+    JA = "ja"
+    PT_BR = "pt-BR"
+    ZH = "zh"
+
+    @property
+    def display_name(self) -> str:
+        """Human-readable language name."""
+        _names = {
+            "en-US": "American English",
+            "en-GB": "British English",
+            "es": "Spanish",
+            "fr": "French",
+            "hi": "Hindi",
+            "it": "Italian",
+            "ja": "Japanese",
+            "pt-BR": "Brazilian Portuguese",
+            "zh": "Mandarin Chinese",
+        }
+        return _names[self.value]
+
+    @property
+    def is_cjk(self) -> bool:
+        """True for CJK languages (Chinese, Japanese)."""
+        return self in (self.ZH, self.JA)
+
+    @property
+    def supports_subtitle_tokens(self) -> bool:
+        """True if this language generates timestamped tokens for subtitles."""
+        return self in (self.EN_US, self.EN_GB)
+
+    @classmethod
+    def from_str(cls, value: str) -> Language:
+        """Parse from user input: ISO code, case-insensitive."""
+        if isinstance(value, Language):
+            return value
+        normalized = value.strip()
+        for member in cls:
+            if member.value.lower() == normalized.lower():
+                return member
+        raise ValueError(f"Invalid Language: {value!r}. Valid: {[m.value for m in cls]}")

abogen/domain/output_paths.py

@@ -76,7 +76,7 @@ def sanitize_filename_for_chapter(title: str, index: int, max_len: int = 80) ->
     return f"{index:02d}_{sanitized}"
 
 
-def sanitize_output_stem(name: str) -> str:
+def sanitize_output_stem(name: str, index: int = 0) -> str:
     base = Path(name or "").stem
     sanitized = _OUTPUT_SANITIZE_RE.sub("_", base).strip("_")
     return sanitized or "output"
@@ -99,6 +99,9 @@ def apply_newline_policy(chapters: List[ExtractedChapter], replace_single_newlin
         chapter.text = newline_regex.sub(" ", chapter.text)
 
 
+from abogen.domain.enums import SaveMode
+
+
 def resolve_output_directory(
     *,
     save_mode: str,
@@ -108,13 +111,13 @@ def resolve_output_directory(
     user_output_path: Optional[Path],
     user_cache_outputs: Optional[Path],
 ) -> Path:
-    if save_mode == "Save to Desktop" and desktop_dir:
+    if save_mode in (SaveMode.SAVE_TO_DESKTOP, "Save to Desktop") and desktop_dir:
         return desktop_dir
-    if save_mode == "Save next to input file":
+    if save_mode in (SaveMode.SAVE_NEXT_TO_INPUT, "Save next to input file"):
         return stored_path.parent
-    if save_mode == "Choose output folder" and output_folder:
+    if save_mode in (SaveMode.CHOOSE_OUTPUT_FOLDER, "Choose output folder") and output_folder:
         return Path(output_folder)
-    if save_mode == "Use default save location" and user_output_path:
+    if save_mode in (SaveMode.DEFAULT_OUTPUT, "Use default save location") and user_output_path:
         return user_output_path
     return user_cache_outputs or Path(".")
 

abogen/domain/pipeline_factory.py

@@ -9,9 +9,23 @@ from __future__ import annotations
 from typing import Any, Dict, Optional
 
 from abogen.domain.device import select_device
+from abogen.domain.enums import Language
 from abogen.domain.voice_resolution import initialize_voice_cache
 from abogen.tts_plugin.utils import create_pipeline, is_plugin_registered
 
+# Kokoro-specific language mapping (engine's responsibility)
+_KOKORO_LANG_MAP = {
+    Language.EN_US: "a",
+    Language.EN_GB: "b",
+    Language.ES: "e",
+    Language.FR: "f",
+    Language.HI: "h",
+    Language.IT: "i",
+    Language.JA: "j",
+    Language.PT_BR: "p",
+    Language.ZH: "z",
+}
+
 
 def resolve_device(use_gpu: bool) -> str:
     """Determine compute device from job and global config flags."""
@@ -36,11 +50,18 @@ def create_pipeline_for_job(
     if not is_plugin_registered(provider):
         provider = "kokoro"
 
+    # Convert Language enum to Kokoro single-letter code
+    try:
+        lang = Language.from_str(language) if not isinstance(language, Language) else language
+    except ValueError:
+        lang = Language.EN_US  # fallback for unknown languages
+    kokoro_code = _KOKORO_LANG_MAP.get(lang, "a")
+
     if provider == "supertonic":
         return create_pipeline("supertonic")
 
     device = resolve_device(use_gpu)
-    return create_pipeline("kokoro", lang_code=language, device=device)
+    return create_pipeline("kokoro", lang_code=kokoro_code, device=device)
 
 
 def dispose_pipelines(pipelines: Dict[str, Any]) -> None:

abogen/domain/split_pattern.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 """Unified split pattern logic extracted from 3 copies."""
 import re
 
+from abogen.domain.enums import Language, SubtitleMode
 
 PUNCTUATION_SENTENCE = r".!?。！？"
 PUNCTUATION_SENTENCE_COMMA = r".!?,。！？、，"
@@ -18,23 +19,32 @@ def get_split_pattern(language: str, subtitle_mode: str) -> str:
     Returns:
         Split pattern string
     """
+    try:
+        lang = Language.from_str(language) if not isinstance(language, Language) else language
+    except ValueError:
+        lang = None  # unknown language — treat as non-English, non-CJK
+    try:
+        mode = SubtitleMode.from_str(subtitle_mode) if not isinstance(subtitle_mode, SubtitleMode) else subtitle_mode
+    except ValueError:
+        mode = SubtitleMode.DISABLED
+
     # For English, always use newline splitting only
-    if language in ("a", "b"):
+    if lang in (Language.EN_US, Language.EN_GB):
         return "\n"
 
     # Determine spacing pattern based on language
-    spacing = r"\s*" if language in ("z", "j") else r"\s+"
+    spacing = r"\s*" if lang and lang.is_cjk else r"\s+"
 
     # For CJK languages, when subtitle mode is Disabled or Line, prefer
     # punctuation-based splitting instead of plain newline splitting.
-    if subtitle_mode in ("Disabled", "Line") and language in ("z", "j"):
+    if mode in (SubtitleMode.DISABLED, SubtitleMode.LINE) and lang and lang.is_cjk:
         return rf"(?<=[{PUNCTUATION_SENTENCE}]){spacing}|\n+"
 
-    if subtitle_mode == "Line":
+    if mode == SubtitleMode.LINE:
         return "\n"
-    elif subtitle_mode == "Sentence":
+    elif mode == SubtitleMode.SENTENCE:
         return rf"(?<=[{PUNCTUATION_SENTENCE}]){spacing}|\n+"
-    elif subtitle_mode == "Sentence + Comma":
+    elif mode == SubtitleMode.SENTENCE_COMMA:
         return rf"(?<=[{PUNCTUATION_SENTENCE_COMMA}]){spacing}|\n+"
     else:
         return r"\n+"

abogen/domain/subtitle_generation.py

@@ -10,6 +10,8 @@ from __future__ import annotations
 import re
 from typing import List, Optional, Tuple
 
+from abogen.domain.enums import Language, SubtitleMode
+
 
 # Punctuation constants for sentence splitting
 PUNCTUATION_SENTENCE = ".!?\u061f\u3002\uff01\uff1f"  # .!? .?. ??
@@ -50,17 +52,17 @@ def process_subtitle_tokens(
     # spaCy is disabled when subtitle mode is "Disabled" or "Line"
     use_spacy_for_english = (
         use_spacy_segmentation
-        and subtitle_mode not in ["Disabled", "Line"]
+        and subtitle_mode not in [SubtitleMode.DISABLED, SubtitleMode.LINE]
-        and lang_code in ["a", "b"]
+        and lang_code in [Language.EN_US, Language.EN_GB]
-        and subtitle_mode in ["Sentence", "Sentence + Comma"]
+        and subtitle_mode in [SubtitleMode.SENTENCE, SubtitleMode.SENTENCE_COMMA]
     )
 
-    if subtitle_mode == "Sentence + Highlighting":
+    if subtitle_mode == SubtitleMode.SENTENCE_HIGHLIGHT:
         _process_karaoke_highlighting(
             processed_tokens, subtitle_entries, max_subtitle_words, fallback_end_time
         )
-    elif subtitle_mode in ["Sentence", "Sentence + Comma", "Line"]:
+    elif subtitle_mode in [SubtitleMode.SENTENCE, SubtitleMode.SENTENCE_COMMA, SubtitleMode.LINE]:
-        if use_spacy_for_english and subtitle_mode != "Line":
+        if use_spacy_for_english and subtitle_mode != SubtitleMode.LINE:
             _process_spacy_sentences(
                 processed_tokens, subtitle_entries, max_subtitle_words,
                 subtitle_mode, lang_code, fallback_end_time
@@ -176,7 +178,7 @@ def _process_spacy_sentences(
     sentence_boundaries = [sent.end_char for sent in doc.sents]
 
     # For "Sentence + Comma" mode, also split on commas
-    if subtitle_mode == "Sentence + Comma":
+    if subtitle_mode == SubtitleMode.SENTENCE_COMMA:
         comma_positions = [
             i + 1 for i, c in enumerate(full_text) if c == ","
         ]
@@ -242,9 +244,9 @@ def _process_regex_sentences(
 ) -> None:
     """Process tokens using regex for sentence boundary detection."""
     # Define separator pattern based on mode
-    if subtitle_mode == "Line":
+    if subtitle_mode == SubtitleMode.LINE:
         separator = r"\n"
-    elif subtitle_mode == "Sentence":
+    elif subtitle_mode == SubtitleMode.SENTENCE:
         # Use punctuation without comma
         separator = rf"[{re.escape(PUNCTUATION_SENTENCE)}]"
     else:  # Sentence + Comma

abogen/domain/voice_loader.py

@@ -33,6 +33,10 @@ class VoiceCache:
         """Clear all cached voices."""
         self._cache.clear()
 
+    def keys(self):
+        """Return cached voice specs."""
+        return self._cache.keys()
+
     def __contains__(self, voice_spec: str) -> bool:
         return self.contains(voice_spec)
 

abogen/infrastructure/subtitle_writer.py

@@ -6,23 +6,10 @@ from enum import Enum
 from pathlib import Path
 from typing import List, Optional, TextIO
 
+from abogen.domain.enums import SubtitleFormat, SubtitleMode
 from abogen.subtitle_utils import clean_subtitle_text
 
 
-class SubtitleFormat(Enum):
-    SRT = "srt"
-    ASS = "ass"
-    VTT = "vtt"
-
-
-class SubtitleMode(Enum):
-    DISABLED = "Disabled"
-    LINE = "Line"
-    SENTENCE = "Sentence"
-    SENTENCE_COMMA = "Sentence + Comma"
-    SENTENCE_HIGHLIGHT = "Sentence + Highlighting"
-
-
 class SubtitleAlignment(Enum):
     LEFT = "left"
     CENTER = "center"

abogen/pyqt/conversion.py

@@ -36,7 +36,7 @@ from abogen.domain.output_paths import (
 )
 from abogen.domain.audio_helpers import build_ffmpeg_command, to_float32
 from abogen.domain.audio_sink import AudioSink, open_audio_sink
-from abogen.domain.conversion_engine import synthesize_text, SegmentStats, SegmentInfo
+from abogen.domain.conversion_engine import synthesize_text, SynthParams, SegmentStats, SegmentInfo
 from abogen.domain.intro_outro import resolve_intro, resolve_outro
 from abogen.domain.audio_buffer import (
     create_silence,
@@ -773,17 +773,20 @@ class ConversionThread(QThread):
                         etr_start_time=self.etr_start_time,
                         total_characters=self.total_char_count,
                     )
+                    intro_synth = SynthParams(
+                        tts_context=self._tts_context,
+                        stats=intro_stats,
+                        check_cancel=lambda: self.cancel_requested,
+                        on_progress=lambda pct, etr: self.progress_updated.emit(pct, etr),
+                        audio_sink=merged_sink,
+                    )
                     run_tts_segment_loop(
                         text=intro_spec.text,
+                        params=intro_synth,
                         backend=self.backend,
                         voice=loaded_intro_voice,
                         speed=self.speed,
                         split_pattern=self.split_pattern,
-                        stats=intro_stats,
-                        check_cancel=lambda: self.cancel_requested,
-                        on_progress=lambda pct, etr: self.progress_updated.emit(pct, etr),
-                        chapter_sink=None,
-                        audio_sink=merged_sink,
                     )
                     self.processed_char_count = intro_stats.processed_chars
                     current_time = intro_stats.current_time
@@ -1016,18 +1019,26 @@ class ConversionThread(QThread):
                             total_characters=self.total_char_count,
                         )
 
-                        try:
+                        synth_params = SynthParams(
-                            synthesize_text(
-                                text=text_segment,
                             tts_context=self._tts_context,
-                                backend=self.backend,
-                                voice=loaded_voice,
-                                speed=self.speed,
                             stats=stats,
                             check_cancel=_qt_check_cancel,
                             on_progress=_qt_on_progress,
-                                chapter_sink=chapter_sink,
                             audio_sink=merged_sink if merge_chapters_at_end else None,
+                            subtitle_mode=self.subtitle_mode,
+                            max_subtitle_words=self.max_subtitle_words,
+                            lang_code=self.lang_code,
+                            use_spacy_segmentation=getattr(self, "use_spacy_segmentation", False),
+                        )
+
+                        try:
+                            synthesize_text(
+                                text=text_segment,
+                                params=synth_params,
+                                backend=self.backend,
+                                voice=loaded_voice,
+                                speed=self.speed,
+                                chapter_sink=chapter_sink,
                                 on_segment=_qt_on_segment,
                                 split_pattern_override=active_split_pattern,
                             )
@@ -1098,17 +1109,20 @@ class ConversionThread(QThread):
                         etr_start_time=self.etr_start_time,
                         total_characters=self.total_char_count,
                     )
+                    outro_synth = SynthParams(
+                        tts_context=self._tts_context,
+                        stats=outro_stats,
+                        check_cancel=lambda: self.cancel_requested,
+                        on_progress=lambda pct, etr: self.progress_updated.emit(pct, etr),
+                        audio_sink=merged_sink,
+                    )
                     run_tts_segment_loop(
                         text=outro_spec.text,
+                        params=outro_synth,
                         backend=self.backend,
                         voice=loaded_outro_voice,
                         speed=self.speed,
                         split_pattern=self.split_pattern,
-                        stats=outro_stats,
-                        check_cancel=lambda: self.cancel_requested,
-                        on_progress=lambda pct, etr: self.progress_updated.emit(pct, etr),
-                        chapter_sink=None,
-                        audio_sink=merged_sink,
                     )
                     self.processed_char_count = outro_stats.processed_chars
                     current_time = outro_stats.current_time

abogen/pyqt/conversion_adapter.py

@@ -0,0 +1,192 @@
+"""PyQt adapter: ConversionThread -> ConversionRequest.
+
+Converts a PyQt ConversionThread into a ConversionRequest that the application layer can process.
+This adapter is the bridge between the PyQt layer and the application/domain layer.
+
+The adapter is responsible for:
+- Mapping ConversionThread fields to ConversionRequest fields
+- Handling UI-specific state (signals, dialogs, cancellation)
+- Providing PipelineProvider and VoiceResolver implementations
+
+Subtitle file/timestamp special paths remain in ConversionThread.run() early return.
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import Any, Callable, Dict, List, Optional
+
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_ports import ConversionCancelled, ResolvedVoice
+
+
+def build_conversion_request_from_thread(thread: Any) -> ConversionRequest:
+    """Convert a PyQt ConversionThread into a ConversionRequest.
+
+    This is the primary function that maps thread fields to ConversionRequest.
+    All fields are copied — the request is independent of the thread.
+
+    Args:
+        thread: PyQt ConversionThread instance
+
+    Returns:
+        ConversionRequest with all thread data mapped
+    """
+    # Determine source path
+    source_path = None
+    is_direct_text = getattr(thread, "is_direct_text", False)
+    if not is_direct_text and thread.file_name:
+        source_path = Path(thread.file_name)
+
+    # Determine original filename
+    original_filename = ""
+    if getattr(thread, "from_queue", False):
+        base_path = getattr(thread, "save_base_path", None) or thread.file_name
+    else:
+        base_path = getattr(thread, "display_path", None) or thread.file_name
+
+    if base_path:
+        original_filename = os.path.basename(base_path)
+
+    # Determine output folder
+    output_folder = None
+    if thread.output_folder:
+        output_folder = Path(thread.output_folder)
+
+    return ConversionRequest(
+        # Source
+        source_path=source_path,
+        direct_text=thread.file_name if is_direct_text else None,
+        original_filename=original_filename,
+        # TTS Settings
+        language=thread.lang_code,
+        tts_provider="kokoro",  # PyQt uses Kokoro by default
+        voice=thread.voice,
+        voice_profile=getattr(thread, "voice_profile", None),
+        speed=thread.speed,
+        use_gpu=thread.use_gpu,
+        supertonic_total_steps=getattr(thread, "supertonic_total_steps", 5),
+        # Output Format
+        output_format=thread.output_format,
+        subtitle_mode=thread.subtitle_mode,
+        subtitle_format=getattr(thread, "subtitle_format", "srt"),
+        max_subtitle_words=getattr(thread, "max_subtitle_words", 50),
+        # Save Options
+        save_mode=thread.save_option,
+        output_folder=output_folder,
+        save_chapters_separately=getattr(thread, "save_chapters_separately", False),
+        merge_chapters_at_end=getattr(thread, "merge_chapters_at_end", True),
+        separate_chapters_format=getattr(thread, "separate_chapters_format", "wav"),
+        save_as_project=getattr(thread, "save_as_project", False),
+        # Timing
+        silence_between_chapters=getattr(thread, "silence_duration", 2.0),
+        chapter_intro_delay=getattr(thread, "chapter_intro_delay", 0.0),
+        # Content Processing
+        replace_single_newlines=getattr(thread, "replace_single_newlines", False),
+        read_title_intro=getattr(thread, "read_title_intro", False),
+        read_closing_outro=getattr(thread, "read_closing_outro", True),
+        auto_prefix_chapter_titles=getattr(thread, "auto_prefix_chapter_titles", True),
+        normalize_chapter_opening_caps=getattr(thread, "normalize_chapter_opening_caps", False),
+        # Pronunciation / Normalization
+        pronunciation_overrides=getattr(thread, "pronunciation_overrides", []) or [],
+        manual_overrides=getattr(thread, "manual_overrides", []) or [],
+        heteronym_overrides=getattr(thread, "heteronym_overrides", []) or [],
+        normalization_overrides=getattr(thread, "normalization_overrides", None),
+        # Chapter/Chunk Configuration
+        chapter_overrides=[],  # PyQt doesn't use chapter overrides from GUI
+        chunks=[],  # PyQt doesn't use chunks from GUI
+        chunk_level="paragraph",
+        speaker_mode="single",
+        speakers={},
+        # Metadata
+        metadata_tags=getattr(thread, "metadata_tags", {}) or {},
+        # Artifacts
+        cover_image_path=getattr(thread, "cover_image_path", None),
+        cover_image_mime=getattr(thread, "cover_image_mime", None),
+        generate_epub3=getattr(thread, "generate_epub3", False),
+    )
+
+
+class PyQtEvents:
+    """PyQt implementation of ConversionEvents protocol.
+
+    Wraps a ConversionThread to provide logging, progress, and cancellation.
+    """
+
+    def __init__(self, thread: Any):
+        self._thread = thread
+
+    def log(self, message: str, level: str = "info") -> None:
+        """Log a message via signal."""
+        self._thread.log_updated.emit((message, _level_to_color(level)))
+
+    def progress(self, pct: int, etr: str) -> None:
+        """Update progress via signal."""
+        self._thread.progress_updated.emit(pct, etr)
+
+    def check_cancelled(self) -> None:
+        """Check if conversion was cancelled.
+
+        Raises:
+            ConversionCancelled: If cancellation was requested
+        """
+        if self._thread.cancel_requested:
+            raise ConversionCancelled("Conversion cancelled by user")
+
+
+class PyQtPipelineProvider:
+    """PyQt implementation of PipelineProvider protocol.
+
+    Wraps the existing backend from ConversionThread.
+    """
+
+    def __init__(self, backend: Any):
+        self._backend = backend
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> Any:
+        """Get a TTS backend instance.
+
+        For PyQt, this returns the pre-initialized backend.
+        """
+        return self._backend
+
+    def dispose_all(self) -> None:
+        """Dispose all backend resources."""
+        pass  # PyQt manages backend lifecycle in thread
+
+
+class PyQtVoiceResolver:
+    """PyQt implementation of VoiceResolver protocol.
+
+    Wraps load_voice_cached from the ConversionThread.
+    """
+
+    def __init__(self, thread: Any):
+        self._thread = thread
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        from abogen.domain.voice_resolution import resolve_fallback_voice_spec
+
+        # Use thread's load_voice_cached method
+        loaded_voice = self._thread.load_voice_cached(voice_spec, self._thread.backend)
+
+        return ResolvedVoice(
+            provider="kokoro",
+            resolved_spec=voice_spec,
+            voice=loaded_voice,
+            speed=self._thread.speed,
+            supertonic_steps=getattr(self._thread, "supertonic_total_steps", 5),
+        )
+
+
+def _level_to_color(level: str) -> str:
+    """Map log level to PyQt color string."""
+    colors = {
+        "info": "grey",
+        "warning": "orange",
+        "error": "red",
+        "debug": "grey",
+    }
+    return colors.get(level, "grey")

abogen/spacy_utils.py

@@ -2,21 +2,23 @@
 Lazy-loaded spaCy utilities for sentence segmentation.
 """
 
+from abogen.domain.enums import Language
+
 # Cached spaCy module and models (lazy loaded)
 _spacy = None
 _nlp_cache = {}
 
 # Language code to spaCy model mapping
 SPACY_MODELS = {
-    "a": "en_core_web_sm",  # American English
+    Language.EN_US: "en_core_web_sm",
-    "b": "en_core_web_sm",  # British English
+    Language.EN_GB: "en_core_web_sm",
-    "e": "es_core_news_sm",  # Spanish
+    Language.ES: "es_core_news_sm",
-    "f": "fr_core_news_sm",  # French
+    Language.FR: "fr_core_news_sm",
-    "i": "it_core_news_sm",  # Italian
+    Language.IT: "it_core_news_sm",
-    "p": "pt_core_news_sm",  # Brazilian Portuguese
+    Language.PT_BR: "pt_core_news_sm",
-    "z": "zh_core_web_sm",  # Mandarin Chinese
+    Language.ZH: "zh_core_web_sm",
-    "j": "ja_core_news_sm",  # Japanese
+    Language.JA: "ja_core_news_sm",
-    "h": "xx_sent_ud_sm",  # Hindi (multi-language model)
+    Language.HI: "xx_sent_ud_sm",
 }
 
 
@@ -36,10 +38,9 @@ def _load_spacy():
 def get_spacy_model(lang_code, log_callback=None):
     """
     Get or load a spaCy model for the given language code.
-    Downloads the model automatically if not available.
 
     Args:
-        lang_code: Language code (a, b, e, f, etc.)
+        lang_code: Language code or Language enum (e.g., "a", "en-US", Language.EN_US)
         log_callback: Optional function to log messages
 
     Returns:
@@ -58,6 +59,14 @@ def get_spacy_model(lang_code, log_callback=None):
         else:
             print(msg)
 
+    # Normalize to Language enum
+    if not isinstance(lang_code, Language):
+        try:
+            lang_code = Language.from_str(lang_code)
+        except ValueError:
+            log(f"\nspaCy: Unknown language '{lang_code}'...")
+            return None
+
     # Check if model is cached
     if lang_code in _nlp_cache:
         return _nlp_cache[lang_code]

abogen/webui/conversion_adapter.py

@@ -0,0 +1,162 @@
+"""WebUI adapter: Job -> ConversionRequest.
+
+Converts a WebUI Job into a ConversionRequest that the application layer can process.
+This adapter is the bridge between the WebUI layer and the application/domain layer.
+
+The adapter is responsible for:
+- Mapping Job fields to ConversionRequest fields
+- Handling UI-specific state (logs, progress, cancellation)
+- Providing PipelineProvider and VoiceResolver implementations
+
+All conversions happen through this adapter — the application layer
+never accesses Job directly.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Callable, Dict, List, Optional
+
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_ports import ConversionCancelled, ResolvedVoice
+
+
+def build_conversion_request_from_job(job: Any) -> ConversionRequest:
+    """Convert a WebUI Job into a ConversionRequest.
+
+    This is the primary function that maps Job fields to ConversionRequest.
+    All fields are copied — the request is independent of the Job.
+
+    Args:
+        job: WebUI Job instance
+
+    Returns:
+        ConversionRequest with all Job data mapped
+    """
+    return ConversionRequest(
+        # Source
+        source_path=Path(job.stored_path) if job.stored_path else None,
+        original_filename=job.original_filename,
+        # TTS Settings
+        language=job.language,
+        tts_provider=job.tts_provider,
+        voice=job.voice,
+        voice_profile=job.voice_profile,
+        speed=job.speed,
+        use_gpu=job.use_gpu,
+        supertonic_total_steps=job.supertonic_total_steps,
+        # Output Format
+        output_format=job.output_format,
+        subtitle_mode=job.subtitle_mode,
+        subtitle_format=job.subtitle_format,
+        max_subtitle_words=job.max_subtitle_words,
+        # Save Options
+        save_mode=job.save_mode,
+        output_folder=Path(job.output_folder) if job.output_folder else None,
+        save_chapters_separately=job.save_chapters_separately,
+        merge_chapters_at_end=job.merge_chapters_at_end,
+        separate_chapters_format=job.separate_chapters_format,
+        save_as_project=job.save_as_project,
+        # Timing
+        silence_between_chapters=job.silence_between_chapters,
+        chapter_intro_delay=job.chapter_intro_delay,
+        # Content Processing
+        replace_single_newlines=job.replace_single_newlines,
+        read_title_intro=job.read_title_intro,
+        read_closing_outro=job.read_closing_outro,
+        auto_prefix_chapter_titles=job.auto_prefix_chapter_titles,
+        normalize_chapter_opening_caps=job.normalize_chapter_opening_caps,
+        # Pronunciation / Normalization
+        pronunciation_overrides=job.pronunciation_overrides or [],
+        manual_overrides=job.manual_overrides or [],
+        heteronym_overrides=job.heteronym_overrides or [],
+        normalization_overrides=job.normalization_overrides or {},
+        # Chapter/Chunk Configuration
+        chapter_overrides=job.chapters or [],
+        chunks=job.chunks or [],
+        chunk_level=job.chunk_level,
+        speaker_mode=job.speaker_mode,
+        speakers=job.speakers or {},
+        # Metadata
+        metadata_tags=job.metadata_tags or {},
+        # Artifacts
+        cover_image_path=Path(job.cover_image_path) if job.cover_image_path else None,
+        cover_image_mime=job.cover_image_mime,
+        generate_epub3=job.generate_epub3,
+    )
+
+
+class WebJobEvents:
+    """WebUI implementation of ConversionEvents protocol.
+
+    Wraps a Job to provide logging, progress, and cancellation.
+    """
+
+    def __init__(self, job: Any):
+        self._job = job
+
+    def log(self, message: str, level: str = "info") -> None:
+        """Log a message to the Job."""
+        self._job.add_log(message, level=level)
+
+    def progress(self, pct: int, etr: str) -> None:
+        """Update progress on the Job."""
+        self._job.progress = pct / 100.0
+        self._job.etr_str = etr
+
+    def check_cancelled(self) -> None:
+        """Check if the Job was cancelled.
+
+        Raises:
+            ConversionCancelled: If cancellation was requested
+        """
+        if self._job.cancel_requested:
+            raise ConversionCancelled("Job cancelled by user")
+
+
+class WebPipelineProvider:
+    """WebUI implementation of PipelineProvider protocol.
+
+    Wraps PipelinePool to provide TTS backends.
+    """
+
+    def __init__(self, pipeline_pool: Any):
+        self._pool = pipeline_pool
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> Any:
+        """Get a TTS backend instance."""
+        return self._pool.get(provider, language, use_gpu)
+
+    def dispose_all(self) -> None:
+        """Dispose all backend resources."""
+        self._pool.dispose_all()
+
+
+class WebVoiceResolver:
+    """WebUI implementation of VoiceResolver protocol.
+
+    Wraps the voice resolution logic from conversion_runner.py.
+    """
+
+    def __init__(
+        self,
+        resolve_fn: Callable[[str], tuple[str, str, Any, Optional[float], Optional[int]]],
+    ):
+        """Initialize with a voice resolution function.
+
+        Args:
+            resolve_fn: Function that takes a voice_spec and returns
+                (provider, resolved_spec, voice_choice, speed, steps)
+        """
+        self._resolve_fn = resolve_fn
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        """Resolve a voice spec into a loaded voice."""
+        provider, resolved_spec, voice, speed, steps = self._resolve_fn(voice_spec)
+        return ResolvedVoice(
+            provider=provider,
+            resolved_spec=resolved_spec,
+            voice=voice,
+            speed=speed or 1.0,
+            supertonic_steps=steps or 5,
+        )

abogen/webui/conversion_runner.py

@@ -117,7 +117,7 @@ from abogen.domain.audio_buffer import (
 )
 from abogen.domain.audio_sink import AudioSink, open_audio_sink
 from abogen.domain.pipeline_factory import PipelinePool
-from abogen.domain.conversion_engine import synthesize_text, process_and_write_subtitles, SegmentStats
+from abogen.domain.conversion_engine import synthesize_text, SynthParams, process_and_write_subtitles, SegmentStats
 from abogen.domain.voice_loader import VoiceCache, resolve_voice
 from abogen.domain.voice_utils import resolve_voice_target as _resolve_voice_target
 
@@ -462,23 +462,27 @@ def run_conversion_job(job: Job) -> None:
                 def _preview(text: str) -> None:
                     job.add_log(f"{prefix}{stats.processed_chars:,}/{job.total_characters or '—'}: {text[:80]}")
 
-                local_segments, accumulated_tokens = synthesize_text(
+                synth_params = SynthParams(
-                    text=source_text,
                     tts_context=tts_context,
-                    backend=backend,
-                    voice=resolved_voice,
-                    speed=effective_speed,
                     stats=stats,
                     check_cancel=canceller,
                     on_progress=_on_progress,
-                    chapter_sink=chapter_sink,
                     audio_sink=audio_sink,
-                    preview_callback=_preview,
                     subtitle_mode=job.subtitle_mode if (subtitle_writer and audio_sink) else "Disabled",
                     max_subtitle_words=job.max_subtitle_words,
                     lang_code=job.language,
                     use_spacy_segmentation=job.subtitle_mode not in ("Disabled", "Line"),
                 )
+
+                local_segments, accumulated_tokens = synthesize_text(
+                    text=source_text,
+                    params=synth_params,
+                    backend=backend,
+                    voice=resolved_voice,
+                    speed=effective_speed,
+                    chapter_sink=chapter_sink,
+                    preview_callback=_preview,
+                )
                 current_time = stats.current_time
 
                 if subtitle_writer and audio_sink and accumulated_tokens:

abogen/webui/routes/utils/synthesize.py

@@ -7,8 +7,22 @@ from flask import current_app, send_file
 from flask.typing import ResponseReturnValue
 
 from abogen.domain.device import select_device as _select_device
+from abogen.domain.enums import Language
 from abogen.domain.split_pattern import get_split_pattern
 
+# Kokoro-specific language mapping (engine's responsibility)
+_KOKORO_LANG_MAP = {
+    Language.EN_US: "a",
+    Language.EN_GB: "b",
+    Language.ES: "e",
+    Language.FR: "f",
+    Language.HI: "h",
+    Language.IT: "i",
+    Language.JA: "j",
+    Language.PT_BR: "p",
+    Language.ZH: "z",
+}
+
 
 SAMPLE_RATE = 24000
 
@@ -45,14 +59,21 @@ def _resolve_pipeline(language: str, use_gpu: bool) -> Tuple[Any, bool]:
 
 
 def get_preview_pipeline(language: str, device: str) -> Any:
-    key = (language, device)
+    # Convert Language enum to Kokoro single-letter code
+    try:
+        lang = Language.from_str(language) if not isinstance(language, Language) else language
+    except ValueError:
+        lang = Language.EN_US
+    kokoro_code = _KOKORO_LANG_MAP.get(lang, "a")
+
+    key = (kokoro_code, device)
     with _preview_pipeline_lock:
         pipeline = _preview_pipelines.get(key)
         if pipeline is not None:
             return pipeline
         from abogen.tts_plugin.utils import create_pipeline
 
-        pipeline = create_pipeline("kokoro", lang_code=language, device=device)
+        pipeline = create_pipeline("kokoro", lang_code=kokoro_code, device=device)
         _preview_pipelines[key] = pipeline
         return pipeline
 

tests/test_application_coverage.py

@@ -0,0 +1,684 @@
+"""Tests for conversion_service.py, output_layout_service.py, and executor gaps.
+
+Covers the remaining untested code in the application layer.
+"""
+
+import tempfile
+from pathlib import Path
+from typing import Any, List, Optional
+from unittest.mock import MagicMock, patch
+
+import numpy as np
+import pytest
+
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    OutputLayout,
+    SegmentPlan,
+)
+from abogen.application.conversion_ports import ResolvedVoice
+from abogen.domain.normalization import TTSContext
+
+
+# ─── Fake implementations (shared with executor tests) ─────────────
+
+
+class FakeAudioSink:
+    def __init__(self):
+        self.written: List[np.ndarray] = []
+        self.closed = False
+
+    def write(self, audio: np.ndarray) -> None:
+        self.written.append(audio)
+
+    def close(self) -> None:
+        self.closed = True
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+class FakeBackend:
+    def __init__(self):
+        self.synthesized: List[str] = []
+
+    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "") -> List:
+        self.synthesized.append(text)
+
+        class FakeSegment:
+            def __init__(self, text: str):
+                self.graphemes = text
+                self.audio = np.zeros(2400, dtype=np.float32)
+                self.tokens = []
+
+        return [FakeSegment(text)]
+
+
+class FakeEvents:
+    def __init__(self):
+        self.logs = []
+        self.progress_calls = []
+        self.cancelled = False
+
+    def log(self, message: str, level: str = "info") -> None:
+        self.logs.append((message, level))
+
+    def progress(self, pct: int, etr: str) -> None:
+        self.progress_calls.append((pct, etr))
+
+    def check_cancelled(self) -> None:
+        if self.cancelled:
+            raise RuntimeError("Conversion cancelled")
+
+
+class FakePipelineProvider:
+    def __init__(self):
+        self.backends = {}
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> FakeBackend:
+        key = f"{provider}:{language}"
+        if key not in self.backends:
+            self.backends[key] = FakeBackend()
+        return self.backends[key]
+
+    def dispose_all(self) -> None:
+        self.backends.clear()
+
+
+class FakeVoiceResolver:
+    def __init__(self):
+        self.resolved_specs = []
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        self.resolved_specs.append(voice_spec)
+        return ResolvedVoice(
+            provider="kokoro",
+            resolved_spec=voice_spec,
+            voice=voice_spec,
+            speed=1.0,
+            supertonic_steps=5,
+        )
+
+
+# ─── Tests for conversion_service.py ───────────────────────────────
+
+
+class TestConversionService:
+    """Tests for the ConversionService.run_conversion function."""
+
+    def test_simple_conversion(self):
+        """Simple text conversion through the service."""
+        from abogen.application.conversion_service import run_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello world",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+
+            result = run_conversion(req, events, pipeline, resolver)
+
+            assert result is not None
+            assert result.audio_path is not None
+            assert result.audio_path.exists()
+
+    def test_service_logs_pipeline_preparation(self):
+        """Service logs pipeline preparation step."""
+        from abogen.application.conversion_service import run_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+
+            result = run_conversion(req, events, pipeline, resolver)
+
+            log_messages = [msg for msg, _ in events.logs]
+            assert any("Preparing conversion pipeline" in msg for msg in log_messages)
+            assert any("Building conversion plan" in msg for msg in log_messages)
+            assert any("Starting conversion" in msg for msg in log_messages)
+            assert any("Conversion complete" in msg for msg in log_messages)
+
+    def test_service_handles_cancellation(self):
+        """Service propagates cancellation from events."""
+        from abogen.application.conversion_service import run_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            events = FakeEvents()
+            events.cancelled = True
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+
+            with pytest.raises(RuntimeError, match="Conversion cancelled"):
+                run_conversion(req, events, pipeline, resolver)
+
+    def test_service_handles_empty_text(self):
+        """Service raises ValueError for empty text."""
+        from abogen.application.conversion_service import run_conversion
+
+        req = ConversionRequest(direct_text="", voice="M1")
+        events = FakeEvents()
+        pipeline = FakePipelineProvider()
+        resolver = FakeVoiceResolver()
+
+        with pytest.raises(ValueError, match="No text content"):
+            run_conversion(req, events, pipeline, resolver)
+
+    def test_service_multi_chapter(self):
+        """Service handles multi-chapter conversion."""
+        from abogen.application.conversion_service import run_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="<<CHAPTER_MARKER:Ch1>>\nText A\n<<CHAPTER_MARKER:Ch2>>\nText B",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+
+            result = run_conversion(req, events, pipeline, resolver)
+
+            assert result.total_chapters == 2
+
+    def test_service_with_intro_outro(self):
+        """Service handles intro/outro."""
+        from abogen.application.conversion_service import run_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Body text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                read_title_intro=True,
+                read_closing_outro=True,
+                metadata_tags={"title": "Test Book", "author": "Author"},
+            )
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+
+            result = run_conversion(req, events, pipeline, resolver)
+
+            assert result is not None
+
+    def test_service_error_logs_failure(self):
+        """Service logs error when conversion fails."""
+        from abogen.application.conversion_service import run_conversion
+
+        req = ConversionRequest(direct_text="Hello", voice="M1")
+        events = FakeEvents()
+        pipeline = FakePipelineProvider()
+        resolver = FakeVoiceResolver()
+
+        # Mock build_conversion_plan to raise an error
+        with patch("abogen.application.conversion_service.build_conversion_plan", side_effect=RuntimeError("Test error")):
+            with pytest.raises(RuntimeError, match="Test error"):
+                run_conversion(req, events, pipeline, resolver)
+
+            log_messages = [msg for msg, _ in events.logs]
+            assert any("Conversion failed" in msg for msg in log_messages)
+
+
+# ─── Tests for output_layout_service.py ─────────────────────────────
+
+
+class TestOutputLayoutService:
+    """Tests for the output_layout_service module."""
+
+    def test_resolve_output_layout_custom_folder(self):
+        """Output layout with custom folder."""
+        from abogen.application.output_layout_service import resolve_output_layout
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            layout = resolve_output_layout(req)
+
+            assert layout.parent_dir == Path(tmpdir)
+            assert layout.audio_dir == Path(tmpdir)
+
+    def test_resolve_output_layout_source_path(self):
+        """Output layout from source path."""
+        from abogen.application.output_layout_service import resolve_output_layout
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            source = Path(tmpdir) / "test.txt"
+            source.write_text("Hello")
+            req = ConversionRequest(
+                source_path=source,
+                voice="M1",
+                save_mode="save_next_to_input",
+            )
+            layout = resolve_output_layout(req)
+
+            assert layout.parent_dir == Path(tmpdir)
+
+    def test_resolve_output_layout_project(self):
+        """Output layout with save_as_project."""
+        from abogen.application.output_layout_service import resolve_output_layout
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                save_as_project=True,
+                original_filename="test.wav",
+            )
+            layout = resolve_output_layout(req)
+
+            assert layout.project_root is not None
+            assert layout.audio_dir is not None
+
+    def test_resolve_merged_path(self):
+        """Resolve merged output path."""
+        from abogen.application.output_layout_service import resolve_merged_path
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            layout = OutputLayout(
+                parent_dir=Path(tmpdir),
+                audio_dir=Path(tmpdir),
+            )
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                original_filename="book.wav",
+                output_format="wav",
+            )
+            path = resolve_merged_path(layout, req)
+
+            assert path.name == "book.wav"
+            assert path.parent == Path(tmpdir)
+
+    def test_resolve_chapter_path(self):
+        """Resolve chapter output path."""
+        from abogen.application.output_layout_service import resolve_chapter_path
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            layout = OutputLayout(
+                parent_dir=Path(tmpdir),
+                audio_dir=Path(tmpdir),
+            )
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                separate_chapters_format="wav",
+            )
+            path = resolve_chapter_path(layout, req, "Chapter 1", 1)
+
+            assert "01" in path.name
+            assert path.suffix == ".wav"
+
+    def test_resolve_chapter_path_empty_title(self):
+        """Resolve chapter path with empty title."""
+        from abogen.application.output_layout_service import resolve_chapter_path
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            layout = OutputLayout(
+                parent_dir=Path(tmpdir),
+                audio_dir=Path(tmpdir),
+            )
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                separate_chapters_format="wav",
+            )
+            path = resolve_chapter_path(layout, req, "", 3)
+
+            assert "chapter_3" in path.name
+
+    def test_should_merge_output_m4b(self):
+        """m4b format forces merge."""
+        from abogen.application.output_layout_service import should_merge_output
+
+        req = ConversionRequest(
+            direct_text="Hello",
+            voice="M1",
+            output_format="m4b",
+            merge_chapters_at_end=False,
+        )
+        assert should_merge_output(req) is True
+
+    def test_should_merge_output_no_separate(self):
+        """No separate chapters means merge."""
+        from abogen.application.output_layout_service import should_merge_output
+
+        req = ConversionRequest(
+            direct_text="Hello",
+            voice="M1",
+            save_chapters_separately=False,
+        )
+        assert should_merge_output(req) is True
+
+    def test_should_merge_output_separate_and_merge(self):
+        """Separate chapters + merge_at_end means merge."""
+        from abogen.application.output_layout_service import should_merge_output
+
+        req = ConversionRequest(
+            direct_text="Hello",
+            voice="M1",
+            save_chapters_separately=True,
+            merge_chapters_at_end=True,
+        )
+        assert should_merge_output(req) is True
+
+    def test_should_merge_output_separate_no_merge(self):
+        """Separate chapters + no merge_at_end means no merge."""
+        from abogen.application.output_layout_service import should_merge_output
+
+        req = ConversionRequest(
+            direct_text="Hello",
+            voice="M1",
+            save_chapters_separately=True,
+            merge_chapters_at_end=False,
+        )
+        assert should_merge_output(req) is False
+
+
+# ─── Tests for executor gaps ────────────────────────────────────────
+
+
+class TestExecutorGaps:
+    """Tests for uncovered executor branches."""
+
+    def test_executor_no_layout_raises(self):
+        """Executor raises ValueError without output_layout."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        req = ConversionRequest(direct_text="Hello", voice="M1")
+        plan = ConversionPlan(
+            request=req,
+            metadata={},
+            chapters=[],
+            output_layout=None,
+        )
+        events = FakeEvents()
+        pipeline = FakePipelineProvider()
+        resolver = FakeVoiceResolver()
+        tts_context = TTSContext()
+
+        with pytest.raises(ValueError, match="output_layout"):
+            execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+    def test_executor_m4b_forces_merge(self):
+        """Executor forces merge for m4b format."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                output_format="m4b",
+                save_chapters_separately=True,
+                merge_chapters_at_end=False,
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello",
+                        segments=[
+                            SegmentPlan(text="Hello", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+            assert result.audio_path is not None
+            assert result.audio_path.suffix == ".m4b"
+
+    def test_executor_separate_chapters(self):
+        """Executor creates separate chapter files."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                save_chapters_separately=True,
+                merge_chapters_at_end=True,
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="Chapter 1",
+                        original_title="Chapter 1",
+                        body_text="Text A",
+                        segments=[
+                            SegmentPlan(text="Text A", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    ),
+                    ChapterPlan(
+                        index=2,
+                        title="Chapter 2",
+                        original_title="Chapter 2",
+                        body_text="Text B",
+                        segments=[
+                            SegmentPlan(text="Text B", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    ),
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+            assert len(result.chapter_paths) == 2
+
+    def test_executor_no_intro_outro(self):
+        """Executor works without intro/outro."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello",
+                        segments=[
+                            SegmentPlan(text="Hello", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                intro=None,
+                outro=None,
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+            assert result is not None
+            log_messages = [msg for msg, _ in events.logs]
+            assert not any("Title intro" in msg for msg in log_messages)
+            assert not any("Closing outro" in msg for msg in log_messages)
+
+    def test_executor_voice_fallback_on_error(self):
+        """Executor falls back to base voice on resolution error."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        class FailingVoiceResolver:
+            def resolve(self, voice_spec: str) -> ResolvedVoice:
+                if voice_spec == "F1":
+                    raise ValueError("Voice not found")
+                return ResolvedVoice(
+                    provider="kokoro",
+                    resolved_spec=voice_spec,
+                    voice=voice_spec,
+                    speed=1.0,
+                    supertonic_steps=5,
+                )
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello",
+                        segments=[
+                            SegmentPlan(text="Hello", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FailingVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+            assert result is not None
+
+    def test_executor_silence_between_chapters(self):
+        """Executor adds silence between chapters."""
+        from abogen.application.conversion_executor import execute_conversion
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                silence_between_chapters=1.0,
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="Ch1",
+                        original_title="Ch1",
+                        body_text="Text A",
+                        segments=[
+                            SegmentPlan(text="Text A", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    ),
+                    ChapterPlan(
+                        index=2,
+                        title="Ch2",
+                        original_title="Ch2",
+                        body_text="Text B",
+                        segments=[
+                            SegmentPlan(text="Text B", voice_spec="M1", kind="body", source="chapter")
+                        ],
+                        voice_spec="M1",
+                    ),
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(plan, events, pipeline, resolver, tts_context)
+
+            assert result is not None
+            # Check that audio was written (silence + speech)
+            assert len(pipeline.backends) > 0

tests/test_conversion_adapters.py

@@ -0,0 +1,500 @@
+"""Tests for conversion adapters (WebUI + PyQt).
+
+Covers field mapping, event bridging, voice resolution, and cancellation behavior.
+"""
+
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from abogen.application.conversion_request import ConversionRequest
+from abogen.application.conversion_ports import ResolvedVoice
+
+
+# ─── WebUI adapter tests ───────────────────────────────────────────
+
+
+class TestWebUIAdapter:
+    """Test WebUI conversion adapter field mapping."""
+
+    def _make_job(self, **overrides):
+        """Create a mock WebUI Job with default values."""
+        defaults = dict(
+            stored_path="/tmp/test.epub",
+            original_filename="test.epub",
+            language="a",
+            tts_provider="kokoro",
+            voice="M1",
+            voice_profile=None,
+            speed=1.0,
+            use_gpu=False,
+            supertonic_total_steps=5,
+            output_format="wav",
+            subtitle_mode="Disabled",
+            subtitle_format="srt",
+            max_subtitle_words=50,
+            save_mode="save_next_to_input",
+            output_folder=None,
+            save_chapters_separately=False,
+            merge_chapters_at_end=True,
+            separate_chapters_format="wav",
+            save_as_project=False,
+            silence_between_chapters=2.0,
+            chapter_intro_delay=0.0,
+            replace_single_newlines=False,
+            read_title_intro=False,
+            read_closing_outro=False,
+            auto_prefix_chapter_titles=True,
+            normalize_chapter_opening_caps=False,
+            pronunciation_overrides=[],
+            manual_overrides=[],
+            heteronym_overrides=[],
+            normalization_overrides={},
+            chapters=[],
+            chunks=[],
+            chunk_level="paragraph",
+            speaker_mode="single",
+            speakers={},
+            metadata_tags={},
+            cover_image_path=None,
+            cover_image_mime=None,
+            generate_epub3=False,
+            cancel_requested=False,
+        )
+        defaults.update(overrides)
+        return SimpleNamespace(**defaults)
+
+    def test_basic_field_mapping(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        job = self._make_job()
+        req = build_conversion_request_from_job(job)
+
+        assert isinstance(req, ConversionRequest)
+        assert req.source_path == Path("/tmp/test.epub")
+        assert req.original_filename == "test.epub"
+        assert req.language == "a"
+        assert req.voice == "M1"
+        assert req.speed == 1.0
+        assert req.output_format == "wav"
+
+    def test_optional_fields_mapped(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        job = self._make_job(
+            voice_profile="custom_profile",
+            output_folder="/output",
+            cover_image_path="/cover.jpg",
+            cover_image_mime="image/jpeg",
+            metadata_tags={"title": "Test"},
+        )
+        req = build_conversion_request_from_job(job)
+
+        assert req.voice_profile == "custom_profile"
+        assert req.output_folder == Path("/output")
+        assert req.cover_image_path == Path("/cover.jpg")
+        assert req.cover_image_mime == "image/jpeg"
+        assert req.metadata_tags == {"title": "Test"}
+
+    def test_none_paths_result_in_none(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        job = self._make_job(
+            stored_path=None,
+            output_folder=None,
+            cover_image_path=None,
+        )
+        req = build_conversion_request_from_job(job)
+
+        assert req.source_path is None
+        assert req.output_folder is None
+        assert req.cover_image_path is None
+
+    def test_chapter_overrides_mapped(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        chapters = [{"title": "Ch1", "voice": "F1"}]
+        job = self._make_job(chapters=chapters)
+        req = build_conversion_request_from_job(job)
+
+        assert req.chapter_overrides == chapters
+
+    def test_chunks_mapped(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        chunks = [{"text": "Hello", "speaker": "A"}]
+        job = self._make_job(chunks=chunks)
+        req = build_conversion_request_from_job(job)
+
+        assert req.chunks == chunks
+
+    def test_pronunciation_overrides_mapped(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+
+        job = self._make_job(
+            pronunciation_overrides=["word=pron"],
+            manual_overrides=["manual=override"],
+            heteronym_overrides=["read=reed"],
+        )
+        req = build_conversion_request_from_job(job)
+
+        assert req.pronunciation_overrides == ["word=pron"]
+        assert req.manual_overrides == ["manual=override"]
+        assert req.heteronym_overrides == ["read=reed"]
+
+    def test_none_defaults_handled(self):
+        from abogen.webui.conversion_adapter import build_conversion_request_from_job
+        from abogen.domain.enums import Language, OutputFormat, SubtitleMode, SaveMode
+
+        job = self._make_job(
+            language=None,
+            voice=None,
+            speed=None,
+            output_format=None,
+            subtitle_mode=None,
+            save_mode=None,
+            silence_between_chapters=None,
+            chapter_intro_delay=None,
+            supertonic_total_steps=None,
+            max_subtitle_words=None,
+        )
+        req = build_conversion_request_from_job(job)
+
+        # None values pass through adapter; ConversionRequest.__post_init__
+        # applies defaults and clamping for numeric fields.
+        assert req.language == Language.EN_US
+        assert req.speed == 1.0
+        assert req.output_format == OutputFormat.WAV
+        assert req.subtitle_mode == SubtitleMode.DISABLED
+        assert req.save_mode == SaveMode.SAVE_NEXT_TO_INPUT
+        assert req.silence_between_chapters == 2.0
+        assert req.chapter_intro_delay == 0.0
+        assert req.supertonic_total_steps == 5
+        assert req.max_subtitle_words == 50
+
+
+class TestWebUIEvents:
+    """Test WebUI ConversionEvents implementation."""
+
+    def test_log_calls_add_log(self):
+        from abogen.webui.conversion_adapter import WebJobEvents
+
+        job = SimpleNamespace(add_log=MagicMock())
+        events = WebJobEvents(job)
+        events.log("test message", level="info")
+
+        job.add_log.assert_called_once_with("test message", level="info")
+
+    def test_progress_updates_job(self):
+        from abogen.webui.conversion_adapter import WebJobEvents
+
+        job = SimpleNamespace(progress=0.0, etr_str="")
+        events = WebJobEvents(job)
+        events.progress(50, "2m 30s")
+
+        assert job.progress == 0.5
+        assert job.etr_str == "2m 30s"
+
+    def test_check_cancelled_raises(self):
+        from abogen.webui.conversion_adapter import ConversionCancelled, WebJobEvents
+
+        job = SimpleNamespace(cancel_requested=True)
+        events = WebJobEvents(job)
+
+        with pytest.raises(ConversionCancelled):
+            events.check_cancelled()
+
+    def test_check_not_cancelled_passes(self):
+        from abogen.webui.conversion_adapter import WebJobEvents
+
+        job = SimpleNamespace(cancel_requested=False)
+        events = WebJobEvents(job)
+
+        events.check_cancelled()  # Should not raise
+
+
+class TestWebUIPipelineProvider:
+    """Test WebUI PipelineProvider implementation."""
+
+    def test_get_returns_backend(self):
+        from abogen.webui.conversion_adapter import WebPipelineProvider
+
+        backend = MagicMock()
+        pool = SimpleNamespace(get=MagicMock(return_value=backend))
+        provider = WebPipelineProvider(pool)
+
+        result = provider.get("kokoro", "a", False)
+
+        assert result is backend
+        pool.get.assert_called_once_with("kokoro", "a", False)
+
+
+class TestWebUIVoiceResolver:
+    """Test WebUI VoiceResolver implementation."""
+
+    def test_resolve_returns_resolved_voice(self):
+        from abogen.webui.conversion_adapter import WebVoiceResolver
+
+        def resolve_fn(spec):
+            return ("kokoro", spec, "M1", 1.0, 5)
+
+        resolver = WebVoiceResolver(resolve_fn)
+        result = resolver.resolve("M1")
+
+        assert isinstance(result, ResolvedVoice)
+        assert result.provider == "kokoro"
+        assert result.voice == "M1"
+        assert result.speed == 1.0
+        assert result.supertonic_steps == 5
+
+    def test_resolve_none_speed_defaults(self):
+        from abogen.webui.conversion_adapter import WebVoiceResolver
+
+        def resolve_fn(spec):
+            return ("kokoro", spec, "M1", None, None)
+
+        resolver = WebVoiceResolver(resolve_fn)
+        result = resolver.resolve("M1")
+
+        assert result.speed == 1.0
+        assert result.supertonic_steps == 5
+
+
+# ─── PyQt adapter tests ────────────────────────────────────────────
+
+
+class TestPyQtAdapter:
+    """Test PyQt conversion adapter field mapping."""
+
+    def _make_thread(self, **overrides):
+        """Create a mock ConversionThread with default values."""
+        defaults = dict(
+            file_name="/tmp/test.epub",
+            lang_code="a",
+            voice="M1",
+            voice_profile=None,
+            speed=1.0,
+            use_gpu=False,
+            supertonic_total_steps=5,
+            output_format="wav",
+            subtitle_mode="Disabled",
+            subtitle_format="srt",
+            max_subtitle_words=50,
+            save_option="save_next_to_input",
+            output_folder=None,
+            save_chapters_separately=False,
+            merge_chapters_at_end=True,
+            separate_chapters_format="wav",
+            save_as_project=False,
+            silence_duration=2.0,
+            chapter_intro_delay=0.0,
+            replace_single_newlines=False,
+            read_title_intro=False,
+            read_closing_outro=True,
+            auto_prefix_chapter_titles=True,
+            normalize_chapter_opening_caps=False,
+            pronunciation_overrides=[],
+            manual_overrides=[],
+            heteronym_overrides=[],
+            normalization_overrides=None,
+            metadata_tags={},
+            cover_image_path=None,
+            cover_image_mime=None,
+            generate_epub3=False,
+            is_direct_text=False,
+            from_queue=False,
+            display_path=None,
+            save_base_path=None,
+            cancel_requested=False,
+        )
+        defaults.update(overrides)
+        return SimpleNamespace(**defaults)
+
+    def test_basic_field_mapping(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread()
+        req = build_conversion_request_from_thread(thread)
+
+        assert isinstance(req, ConversionRequest)
+        assert req.source_path == Path("/tmp/test.epub")
+        assert req.language == "a"
+        assert req.voice == "M1"
+        assert req.speed == 1.0
+        assert req.output_format == "wav"
+
+    def test_direct_text_mode(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread(
+            is_direct_text=True,
+            file_name="Hello world",
+        )
+        req = build_conversion_request_from_thread(thread)
+
+        assert req.source_path is None
+        assert req.direct_text == "Hello world"
+
+    def test_from_queue_uses_save_base_path(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread(
+            from_queue=True,
+            save_base_path="/queue/book.epub",
+            display_path="/display/book.epub",
+        )
+        req = build_conversion_request_from_thread(thread)
+
+        assert req.original_filename == "book.epub"
+
+    def test_display_path_used_when_not_from_queue(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread(
+            from_queue=False,
+            display_path="/display/book.epub",
+            save_base_path="/queue/book.epub",
+        )
+        req = build_conversion_request_from_thread(thread)
+
+        assert req.original_filename == "book.epub"
+
+    def test_output_folder_mapped(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread(output_folder="/output")
+        req = build_conversion_request_from_thread(thread)
+
+        assert req.output_folder == Path("/output")
+
+    def test_none_defaults_handled(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+        from abogen.domain.enums import Language, OutputFormat, SubtitleMode, SaveMode
+
+        thread = self._make_thread(
+            lang_code=None,
+            voice=None,
+            speed=None,
+            output_format=None,
+            subtitle_mode=None,
+            save_option=None,
+            silence_duration=None,
+            chapter_intro_delay=None,
+            supertonic_total_steps=None,
+            max_subtitle_words=None,
+        )
+        req = build_conversion_request_from_thread(thread)
+
+        # None values pass through adapter; ConversionRequest.__post_init__
+        # applies defaults and clamping for numeric fields.
+        assert req.language == Language.EN_US
+        assert req.speed == 1.0
+        assert req.output_format == OutputFormat.WAV
+        assert req.subtitle_mode == SubtitleMode.DISABLED
+        assert req.save_mode == SaveMode.SAVE_NEXT_TO_INPUT
+        assert req.silence_between_chapters == 2.0
+        assert req.chapter_intro_delay == 0.0
+        assert req.supertonic_total_steps == 5
+        assert req.max_subtitle_words == 50
+
+    def test_chapter_chunks_not_mapped(self):
+        from abogen.pyqt.conversion_adapter import build_conversion_request_from_thread
+
+        thread = self._make_thread()
+        req = build_conversion_request_from_thread(thread)
+
+        assert req.chapter_overrides == []
+        assert req.chunks == []
+        assert req.chunk_level == "paragraph"
+        assert req.speaker_mode == "single"
+        assert req.speakers == {}
+
+
+class TestPyQtEvents:
+    """Test PyQt ConversionEvents implementation."""
+
+    def test_log_emits_signal(self):
+        from abogen.pyqt.conversion_adapter import PyQtEvents
+
+        thread = SimpleNamespace(
+            log_updated=MagicMock(),
+        )
+        events = PyQtEvents(thread)
+        events.log("test message", level="info")
+
+        thread.log_updated.emit.assert_called_once()
+
+    def test_progress_emits_signal(self):
+        from abogen.pyqt.conversion_adapter import PyQtEvents
+
+        thread = SimpleNamespace(
+            progress_updated=MagicMock(),
+        )
+        events = PyQtEvents(thread)
+        events.progress(50, "2m 30s")
+
+        thread.progress_updated.emit.assert_called_once_with(50, "2m 30s")
+
+    def test_check_cancelled_raises(self):
+        from abogen.pyqt.conversion_adapter import ConversionCancelled, PyQtEvents
+
+        thread = SimpleNamespace(cancel_requested=True)
+        events = PyQtEvents(thread)
+
+        with pytest.raises(ConversionCancelled):
+            events.check_cancelled()
+
+    def test_check_not_cancelled_passes(self):
+        from abogen.pyqt.conversion_adapter import PyQtEvents
+
+        thread = SimpleNamespace(cancel_requested=False)
+        events = PyQtEvents(thread)
+
+        events.check_cancelled()  # Should not raise
+
+
+class TestPyQtPipelineProvider:
+    """Test PyQt PipelineProvider implementation."""
+
+    def test_get_returns_backend(self):
+        from abogen.pyqt.conversion_adapter import PyQtPipelineProvider
+
+        backend = MagicMock()
+        provider = PyQtPipelineProvider(backend)
+
+        result = provider.get("kokoro", "a", False)
+
+        assert result is backend
+
+    def test_dispose_all_noop(self):
+        from abogen.pyqt.conversion_adapter import PyQtPipelineProvider
+
+        backend = MagicMock()
+        provider = PyQtPipelineProvider(backend)
+
+        provider.dispose_all()  # Should not raise
+
+
+class TestPyQtVoiceResolver:
+    """Test PyQt VoiceResolver implementation."""
+
+    def test_resolve_returns_resolved_voice(self):
+        from abogen.pyqt.conversion_adapter import PyQtVoiceResolver
+
+        loaded_voice = MagicMock()
+        thread = SimpleNamespace(
+            load_voice_cached=MagicMock(return_value=loaded_voice),
+            backend=MagicMock(),
+            speed=1.0,
+            supertonic_total_steps=5,
+        )
+        resolver = PyQtVoiceResolver(thread)
+        result = resolver.resolve("M1")
+
+        assert isinstance(result, ResolvedVoice)
+        assert result.provider == "kokoro"
+        assert result.voice is loaded_voice
+        assert result.speed == 1.0
+        assert result.supertonic_steps == 5

tests/test_conversion_executor.py

@@ -0,0 +1,413 @@
+"""Regression tests for conversion executor logic.
+
+These tests verify that the core conversion engine (synthesize_text,
+run_tts_segment_loop, process_and_write_subtitles) works correctly
+with fake backends and sinks. They serve as a regression net for the
+upcoming conversion flow unification refactor.
+
+All tests use mock/fake implementations — no real TTS, no real audio I/O.
+"""
+
+import pytest
+import numpy as np
+from unittest.mock import MagicMock, patch
+from dataclasses import dataclass, field
+from typing import Any
+
+from abogen.domain.conversion_engine import (
+    synthesize_text,
+    SynthParams,
+    run_tts_segment_loop,
+    process_and_write_subtitles,
+    SegmentStats,
+    SegmentInfo,
+    CancelChecker,
+)
+from abogen.domain.normalization import TTSContext
+from abogen.domain.audio_sink import AudioSink
+
+
+# ─── Fake Implementations ──────────────────────────────────────────
+
+class FakeAudioSink:
+    """Fake audio sink that records written data."""
+
+    def __init__(self):
+        self.written = []
+        self.closed = False
+
+    def write(self, audio: np.ndarray) -> None:
+        self.written.append(audio)
+
+    def close(self) -> None:
+        self.closed = True
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+class FakeBackend:
+    """Fake TTS backend that returns deterministic audio."""
+
+    def __init__(self, segment_duration: float = 0.5):
+        self.segment_duration = segment_duration
+        self.call_count = 0
+
+    def __call__(self, text: str, voice: Any, speed: float = 1.0, split_pattern: str = ""):
+        self.call_count += 1
+        # Return fake segment objects with required attributes
+        @dataclass
+        class FakeSegment:
+            graphemes: str = ""
+            audio: Any = None
+            tokens: list = field(default_factory=list)
+
+        samples = int(24000 * self.segment_duration)
+        audio = np.zeros(samples, dtype=np.float32)
+        tokens = [
+            MagicMock(start_ts=0.0, end_ts=0.3, text="Hello", whitespace=" "),
+            MagicMock(start_ts=0.3, end_ts=0.5, text="world", whitespace="."),
+        ]
+        return [FakeSegment(graphemes=text, audio=audio, tokens=tokens)]
+
+
+class FakeSubtitleWriter:
+    """Fake subtitle writer that records entries."""
+
+    def __init__(self):
+        self.entries = []
+        self.opened = False
+        self.closed = False
+
+    def open(self) -> None:
+        self.opened = True
+
+    def write_entry(self, start: float, end: float, text: str) -> None:
+        self.entries.append((start, end, text))
+
+    def close(self) -> None:
+        self.closed = True
+
+    def __enter__(self):
+        self.open()
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+# ─── SegmentStats Tests ────────────────────────────────────────────
+
+class TestSegmentStats:
+    """Verify SegmentStats tracks timing and character counts."""
+
+    def test_default_values(self):
+        stats = SegmentStats()
+        assert stats.processed_chars == 0
+        assert stats.current_time == 0.0
+        assert stats.total_characters == 0
+
+    def test_mutation(self):
+        stats = SegmentStats(total_characters=1000)
+        stats.processed_chars += 100
+        stats.current_time += 1.5
+        assert stats.processed_chars == 100
+        assert stats.current_time == 1.5
+
+
+# ─── synthesize_text Tests ─────────────────────────────────────────
+
+class TestSynthesizeText:
+    """Verify synthesize_text normalizes and runs TTS correctly."""
+
+    def test_basic_synthesis(self):
+        backend = FakeBackend()
+        tts_ctx = TTSContext()
+        stats = SegmentStats(total_characters=100)
+        sink = FakeAudioSink()
+
+        cancel = lambda: False
+        progress_calls = []
+        def on_progress(pct, etr):
+            progress_calls.append((pct, etr))
+
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel,
+            on_progress=on_progress,
+            audio_sink=sink,
+        )
+
+        segments, tokens = synthesize_text(
+            text="Hello world.",
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+        )
+
+        assert segments >= 1
+        assert len(sink.written) >= 1
+        assert len(progress_calls) >= 1
+
+    def test_cancellation(self):
+        backend = FakeBackend()
+        tts_ctx = TTSContext()
+        stats = SegmentStats(total_characters=10000)
+
+        cancel = lambda: True  # Always cancel
+        progress_calls = []
+        def on_progress(pct, etr):
+            progress_calls.append((pct, etr))
+
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel,
+            on_progress=on_progress,
+        )
+
+        segments, tokens = synthesize_text(
+            text="Hello world.",
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+        )
+
+        # Should stop early due to cancellation
+        assert segments == 0
+
+    def test_with_chapter_sink(self):
+        backend = FakeBackend()
+        tts_ctx = TTSContext()
+        stats = SegmentStats(total_characters=100)
+        merged_sink = FakeAudioSink()
+        chapter_sink = FakeAudioSink()
+
+        cancel = lambda: False
+        def on_progress(pct, etr):
+            pass
+
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel,
+            on_progress=on_progress,
+            audio_sink=merged_sink,
+        )
+
+        segments, tokens = synthesize_text(
+            text="Hello world.",
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+            chapter_sink=chapter_sink,
+        )
+
+        # Both sinks should receive audio
+        assert len(chapter_sink.written) >= 1
+        assert len(merged_sink.written) >= 1
+
+    def test_split_pattern_override(self):
+        backend = FakeBackend()
+        tts_ctx = TTSContext(split_pattern=r"(?<=[.!?\-])\s+")
+        stats = SegmentStats(total_characters=100)
+
+        cancel = lambda: False
+        def on_progress(pct, etr):
+            pass
+
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel,
+            on_progress=on_progress,
+        )
+
+        segments, tokens = synthesize_text(
+            text="Hello world.",
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+            split_pattern_override=r"\n+",
+        )
+
+        assert segments >= 1
+
+
+# ─── process_and_write_subtitles Tests ──────────────────────────────
+
+class TestProcessAndWriteSubtitles:
+    """Verify subtitle processing writes entries correctly."""
+
+    def test_empty_tokens(self):
+        writer = FakeSubtitleWriter()
+        process_and_write_subtitles(
+            [],
+            writer,
+            subtitle_mode="Sentence",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+            fallback_end_time=10.0,
+        )
+        assert len(writer.entries) == 0
+
+    def test_sentence_mode_entries(self):
+        writer = FakeSubtitleWriter()
+        tokens = [
+            {"start": 0.0, "end": 0.5, "text": "Hello", "whitespace": " "},
+            {"start": 0.5, "end": 1.0, "text": "world", "whitespace": "."},
+        ]
+        process_and_write_subtitles(
+            tokens,
+            writer,
+            subtitle_mode="Sentence",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+            fallback_end_time=2.0,
+        )
+        assert len(writer.entries) >= 1
+        start, end, text = writer.entries[0]
+        assert start < end
+        assert isinstance(text, str)
+
+    def test_line_mode_entries(self):
+        writer = FakeSubtitleWriter()
+        tokens = [
+            {"start": 0.0, "end": 0.5, "text": "Hello", "whitespace": " "},
+            {"start": 0.5, "end": 1.0, "text": "world", "whitespace": "\n"},
+            {"start": 1.0, "end": 1.5, "text": "New", "whitespace": " "},
+            {"start": 1.5, "end": 2.0, "text": "line", "whitespace": "."},
+        ]
+        process_and_write_subtitles(
+            tokens,
+            writer,
+            subtitle_mode="Line",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+            fallback_end_time=3.0,
+        )
+        assert len(writer.entries) >= 1
+
+    def test_disabled_mode(self):
+        """Disabled mode is checked by the caller (run_tts_segment_loop),
+        not by process_subtitle_tokens itself. This test verifies that
+        process_subtitle_tokens still processes when called directly."""
+        writer = FakeSubtitleWriter()
+        tokens = [
+            {"start": 0.0, "end": 0.5, "text": "Hello", "whitespace": " "},
+        ]
+        process_and_write_subtitles(
+            tokens,
+            writer,
+            subtitle_mode="Disabled",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+            fallback_end_time=2.0,
+        )
+        # process_subtitle_tokens doesn't filter by mode — caller must check
+        # So entries may be written even in "Disabled" mode
+        assert isinstance(writer.entries, list)
+
+
+# ─── Integration: Full Pipeline ─────────────────────────────────────
+
+class TestFullPipeline:
+    """Integration tests for the complete TTS pipeline."""
+
+    def test_end_to_end_synthesis(self):
+        backend = FakeBackend()
+        tts_ctx = TTSContext()
+        stats = SegmentStats(total_characters=50)
+        merged_sink = FakeAudioSink()
+        chapter_sink = FakeAudioSink()
+        subtitle_writer = FakeSubtitleWriter()
+
+        cancel = lambda: False
+        progress_calls = []
+        def on_progress(pct, etr):
+            progress_calls.append((pct, etr))
+
+        # Simulate full pipeline: synthesize → subtitles → finalize
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel,
+            on_progress=on_progress,
+            audio_sink=merged_sink,
+            subtitle_mode="Sentence",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+        )
+
+        segments, tokens = synthesize_text(
+            text="This is a test sentence. Another sentence here.",
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+            chapter_sink=chapter_sink,
+        )
+
+        # Process accumulated tokens
+        process_and_write_subtitles(
+            tokens,
+            subtitle_writer,
+            subtitle_mode="Sentence",
+            max_subtitle_words=5,
+            lang_code="a",
+            use_spacy_segmentation=False,
+            fallback_end_time=stats.current_time,
+        )
+
+        # Verify results
+        assert segments >= 1
+        assert len(merged_sink.written) >= 1
+        assert len(chapter_sink.written) >= 1
+        assert stats.processed_chars > 0
+        assert stats.current_time > 0
+
+    def test_multi_segment_with_cancel(self):
+        """Test that cancellation works mid-pipeline."""
+        backend = FakeBackend()
+        tts_ctx = TTSContext()
+        stats = SegmentStats(total_characters=10000)
+
+        cancel_count = [0]
+        def cancel_fn():
+            cancel_count[0] += 1
+            return cancel_count[0] > 3  # Cancel after 3 segments
+
+        progress_calls = []
+        def on_progress(pct, etr):
+            progress_calls.append((pct, etr))
+
+        params = SynthParams(
+            tts_context=tts_ctx,
+            stats=stats,
+            check_cancel=cancel_fn,
+            on_progress=on_progress,
+        )
+
+        segments, tokens = synthesize_text(
+            text="Hello world. " * 100,
+            params=params,
+            backend=backend,
+            voice="M1",
+            speed=1.0,
+        )
+
+        # Should have stopped before processing all text
+        assert segments <= 4

tests/test_conversion_executor_unified.py

@@ -0,0 +1,513 @@
+"""Tests for the unified conversion executor (execute_conversion).
+
+Uses fake/mock objects for ports (events, pipeline_provider, voice_resolver)
+to test the executor without real TTS or audio I/O.
+"""
+
+import tempfile
+from pathlib import Path
+from typing import Any, List, Optional
+from unittest.mock import MagicMock
+
+import numpy as np
+import pytest
+
+from abogen.application.conversion_executor import execute_conversion
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    OutputLayout,
+    SegmentPlan,
+)
+from abogen.application.conversion_ports import ResolvedVoice
+from abogen.application.conversion_request import ConversionRequest
+from abogen.domain.normalization import TTSContext
+
+
+# ─── Fake implementations ──────────────────────────────────────────
+
+
+class FakeAudioSink:
+    """Fake audio sink that collects written audio data."""
+
+    def __init__(self):
+        self.written: List[np.ndarray] = []
+        self.closed = False
+
+    def write(self, audio: np.ndarray) -> None:
+        self.written.append(audio)
+
+    def close(self) -> None:
+        self.closed = True
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        self.close()
+
+
+class FakeSubtitleWriter:
+    """Fake subtitle writer that collects entries."""
+
+    def __init__(self, path: Optional[Path] = None):
+        self.path = path or Path("/fake/output.srt")
+        self.entries = []
+        self.closed = False
+
+    def open(self) -> None:
+        pass
+
+    def write_entry(self, start: float, end: float, text: str) -> None:
+        self.entries.append((start, end, text))
+
+    def close(self) -> None:
+        self.closed = True
+
+
+class FakeBackend:
+    """Fake TTS backend that returns silent audio segments."""
+
+    def __init__(self):
+        self.synthesized: List[str] = []
+
+    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "") -> List:
+        """Return fake TTS segments."""
+        self.synthesized.append(text)
+
+        # Create a fake segment object
+        class FakeSegment:
+            def __init__(self, text: str):
+                self.graphemes = text
+                self.audio = np.zeros(2400, dtype=np.float32)  # 0.1s at 24kHz
+                self.tokens = []
+
+        return [FakeSegment(text)]
+
+
+class FakeEvents:
+    """Fake conversion events that collect logs and progress."""
+
+    def __init__(self):
+        self.logs = []
+        self.progress_calls = []
+        self.cancelled = False
+
+    def log(self, message: str, level: str = "info") -> None:
+        self.logs.append((message, level))
+
+    def progress(self, pct: int, etr: str) -> None:
+        self.progress_calls.append((pct, etr))
+
+    def check_cancelled(self) -> None:
+        if self.cancelled:
+            raise RuntimeError("Conversion cancelled")
+
+
+class FakePipelineProvider:
+    """Fake pipeline provider that returns FakeBackend."""
+
+    def __init__(self):
+        self.backends = {}
+
+    def get(self, provider: str, language: str, use_gpu: bool) -> FakeBackend:
+        key = f"{provider}:{language}"
+        if key not in self.backends:
+            self.backends[key] = FakeBackend()
+        return self.backends[key]
+
+    def dispose_all(self) -> None:
+        self.backends.clear()
+
+
+class FakeVoiceResolver:
+    """Fake voice resolver that returns ResolvedVoice objects."""
+
+    def __init__(self):
+        self.resolved_specs = []
+
+    def resolve(self, voice_spec: str) -> ResolvedVoice:
+        self.resolved_specs.append(voice_spec)
+        return ResolvedVoice(
+            provider="kokoro",
+            resolved_spec=voice_spec,
+            voice=voice_spec,  # Use spec as voice name
+            speed=1.0,
+            supertonic_steps=5,
+        )
+
+
+# ─── Tests ──────────────────────────────────────────────────────────
+
+
+class TestExecuteConversion:
+    """Tests for the main execute_conversion function."""
+
+    def test_simple_text_conversion(self):
+        """Simple text conversion without chapters."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello world",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello world",
+                        segments=[
+                            SegmentPlan(
+                                text="Hello world",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            assert result is not None
+            assert result.audio_path is not None
+            assert result.audio_path.exists()
+
+    def test_multi_chapter_conversion(self):
+        """Multi-chapter conversion."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+                save_chapters_separately=True,
+                merge_chapters_at_end=True,
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="Chapter 1",
+                        original_title="Chapter 1",
+                        body_text="First chapter text",
+                        segments=[
+                            SegmentPlan(
+                                text="First chapter text",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    ),
+                    ChapterPlan(
+                        index=2,
+                        title="Chapter 2",
+                        original_title="Chapter 2",
+                        body_text="Second chapter text",
+                        segments=[
+                            SegmentPlan(
+                                text="Second chapter text",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    ),
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            assert result.total_chapters == 2
+            assert len(result.chapter_paths) == 2
+
+    def test_voice_markers(self):
+        """Conversion with voice markers creates separate segments."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello World",
+                        segments=[
+                            SegmentPlan(
+                                text="Hello",
+                                voice_spec="M1",
+                                kind="body",
+                                source="voice_marker",
+                            ),
+                            SegmentPlan(
+                                text="World",
+                                voice_spec="F1",
+                                kind="body",
+                                source="voice_marker",
+                            ),
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            assert result is not None
+            assert len(result.chunk_markers) == 2
+
+    def test_intro_outro(self):
+        """Conversion with intro and outro."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Body text",
+                        segments=[
+                            SegmentPlan(
+                                text="Body text",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                intro=IntroOutroSpec(
+                    enabled=True,
+                    text="Book intro text",
+                    voice_spec="M1",
+                    kind="intro",
+                ),
+                outro=IntroOutroSpec(
+                    enabled=True,
+                    text="Book outro text",
+                    voice_spec="M1",
+                    kind="outro",
+                ),
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            assert result is not None
+            # Check that intro/outro were logged
+            log_messages = [msg for msg, _ in events.logs]
+            assert any("Title intro" in msg for msg in log_messages)
+            assert any("Closing outro" in msg for msg in log_messages)
+
+    def test_cancellation(self):
+        """Conversion can be cancelled."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Body text",
+                        segments=[
+                            SegmentPlan(
+                                text="Body text",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            events.cancelled = True  # Set cancellation
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            # Should raise RuntimeError when cancelled
+            with pytest.raises(RuntimeError, match="Conversion cancelled"):
+                execute_conversion(
+                    plan, events, pipeline, resolver, tts_context
+                )
+
+    def test_progress_reporting(self):
+        """Progress is reported during conversion."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello world",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Hello world",
+                        segments=[
+                            SegmentPlan(
+                                text="Hello world",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            # Progress should have been reported
+            assert len(events.progress_calls) > 0
+
+    def test_metadata_preserved(self):
+        """Metadata from plan is preserved in result."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Text",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = ConversionPlan(
+                request=req,
+                metadata={"title": "Test Book", "author": "Author"},
+                chapters=[
+                    ChapterPlan(
+                        index=1,
+                        title="text",
+                        original_title="text",
+                        body_text="Text",
+                        segments=[
+                            SegmentPlan(
+                                text="Text",
+                                voice_spec="M1",
+                                kind="body",
+                                source="chapter",
+                            )
+                        ],
+                        voice_spec="M1",
+                    )
+                ],
+                output_layout=OutputLayout(
+                    parent_dir=Path(tmpdir),
+                    audio_dir=Path(tmpdir),
+                ),
+            )
+
+            events = FakeEvents()
+            pipeline = FakePipelineProvider()
+            resolver = FakeVoiceResolver()
+            tts_context = TTSContext()
+
+            result = execute_conversion(
+                plan, events, pipeline, resolver, tts_context
+            )
+
+            assert result.metadata["title"] == "Test Book"
+            assert result.metadata["author"] == "Author"

tests/test_conversion_planner.py

@@ -0,0 +1,560 @@
+"""Tests for the unified conversion planner (build_conversion_plan).
+
+Verifies that the planner correctly handles:
+- Plain text conversion
+- Voice markers (PyQt style)
+- Chapter parsing
+- Chunks (WebUI style)
+- Intro/outro
+- Output layout
+- Edge cases (empty text, no chapters, etc.)
+
+Also includes domain-level regression tests for the underlying functions.
+"""
+
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from abogen.application.conversion_models import (
+    ChapterPlan,
+    ConversionPlan,
+    IntroOutroSpec,
+    OutputLayout,
+    SegmentPlan,
+)
+from abogen.application.conversion_planner import build_conversion_plan
+from abogen.application.conversion_request import ConversionRequest
+
+
+class TestBuildConversionPlan:
+    """Tests for the main build_conversion_plan function."""
+
+    def test_direct_text_simple(self):
+        """Plain text without markers or chapters."""
+        req = ConversionRequest(direct_text="Hello world", voice="M1")
+        plan = build_conversion_plan(req)
+
+        assert isinstance(plan, ConversionPlan)
+        assert len(plan.chapters) == 1
+        assert plan.chapters[0].segments[0].text == "Hello world"
+        assert plan.chapters[0].segments[0].voice_spec == "M1"
+        assert plan.chapters[0].segments[0].source == "chapter"
+
+    def test_direct_text_with_chapters(self):
+        """Text with chapter markers is split into chapters."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Chapter 1>>\nText A\n<<CHAPTER_MARKER:Chapter 2>>\nText B",
+            voice="M1",
+        )
+        plan = build_conversion_plan(req)
+
+        assert len(plan.chapters) == 2
+        assert plan.chapters[0].title == "Chapter 1"
+        assert plan.chapters[1].title == "Chapter 2"
+
+    def test_voice_markers(self):
+        """Voice markers are detected and create separate segments."""
+        req = ConversionRequest(
+            direct_text="Hello <<VOICE:F1>> World", voice="M1"
+        )
+        plan = build_conversion_plan(req)
+
+        segments = plan.chapters[0].segments
+        assert len(segments) == 2
+        assert segments[0].text == "Hello"
+        assert segments[0].source == "voice_marker"
+        assert segments[1].text == "World"
+        assert segments[1].source == "voice_marker"
+
+    def test_chunks(self):
+        """Chunks from WebUI are converted to segments."""
+        req = ConversionRequest(
+            direct_text="Some text",
+            voice="M1",
+            chunks=[
+                {"text": "Chunk 1", "speaker_id": "narrator"},
+                {"text": "Chunk 2", "speaker_id": "narrator"},
+            ],
+        )
+        plan = build_conversion_plan(req)
+
+        segments = plan.chapters[0].segments
+        assert len(segments) == 2
+        assert segments[0].text == "Chunk 1"
+        assert segments[0].source == "chunk"
+        assert segments[1].text == "Chunk 2"
+
+    def test_chunks_with_voice(self):
+        """Chunks with per-chunk voice spec."""
+        req = ConversionRequest(
+            direct_text="Text",
+            voice="M1",
+            chunks=[
+                {"text": "Narrator speaks", "speaker_id": "narrator"},
+                {"text": "Character speaks", "speaker_id": "alice", "voice": "F1"},
+            ],
+            speakers={"alice": {"voice": "F1"}},
+        )
+        plan = build_conversion_plan(req)
+
+        segments = plan.chapters[0].segments
+        assert len(segments) == 2
+        assert segments[0].voice_spec == "M1"
+        assert segments[1].voice_spec == "F1"
+
+    def test_intro_spec(self):
+        """Intro is created when read_title_intro=True."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Chapter 1>>\nThe Great Gatsby by F. Scott Fitzgerald\nBody text",
+            voice="M1",
+            read_title_intro=True,
+            metadata_tags={"title": "The Great Gatsby", "author": "F. Scott Fitzgerald"},
+        )
+        plan = build_conversion_plan(req)
+
+        # Intro may or may not be enabled depending on metadata resolution
+        assert plan.intro is None or isinstance(plan.intro, IntroOutroSpec)
+
+    def test_output_layout(self):
+        """Output layout is resolved from request."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            req = ConversionRequest(
+                direct_text="Hello",
+                voice="M1",
+                save_mode="custom_folder",
+                output_folder=Path(tmpdir),
+            )
+            plan = build_conversion_plan(req)
+
+            assert isinstance(plan.output_layout, OutputLayout)
+            assert plan.output_layout.parent_dir == Path(tmpdir)
+
+    def test_empty_text_raises(self):
+        """Empty text should raise ValueError."""
+        req = ConversionRequest(direct_text="", voice="M1")
+        with pytest.raises(ValueError, match="No text content"):
+            build_conversion_plan(req)
+
+    def test_whitespace_only_raises(self):
+        """Whitespace-only text should raise ValueError."""
+        req = ConversionRequest(direct_text="   \n  \n  ", voice="M1")
+        with pytest.raises(ValueError, match="No text content"):
+            build_conversion_plan(req)
+
+    def test_no_source_raises(self):
+        """Request with no source should raise ValueError."""
+        req = ConversionRequest(voice="M1")
+        with pytest.raises(ValueError, match="No text content"):
+            build_conversion_plan(req)
+
+    def test_plan_preserves_request(self):
+        """Plan should reference the original request."""
+        req = ConversionRequest(direct_text="Hello", voice="M1", speed=1.5)
+        plan = build_conversion_plan(req)
+
+        assert plan.request is req
+        assert plan.request.speed == 1.5
+
+    def test_metadata_in_plan(self):
+        """Metadata from request should appear in plan."""
+        req = ConversionRequest(
+            direct_text="Hello",
+            voice="M1",
+            metadata_tags={"title": "Test Book", "author": "Author"},
+        )
+        plan = build_conversion_plan(req)
+
+        assert "title" in plan.metadata
+        assert plan.metadata["title"] == "Test Book"
+
+    def test_chapter_index_starts_at_1(self):
+        """Chapter indices should start at 1."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Ch1>>\nText\n<<CHAPTER_MARKER:Ch2>>\nText\n<<CHAPTER_MARKER:Ch3>>\nText",
+            voice="M1",
+        )
+        plan = build_conversion_plan(req)
+
+        for i, ch in enumerate(plan.chapters, 1):
+            assert ch.index == i
+
+    def test_chapter_body_text_preserved(self):
+        """Chapter body text should be preserved in ChapterPlan."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Chapter 1>>\nThe actual body text", voice="M1"
+        )
+        plan = build_conversion_plan(req)
+
+        assert "The actual body text" in plan.chapters[0].body_text
+
+    def test_segment_kind_default(self):
+        """Default segment kind should be 'body'."""
+        req = ConversionRequest(direct_text="Hello", voice="M1")
+        plan = build_conversion_plan(req)
+
+        assert plan.chapters[0].segments[0].kind == "body"
+
+
+class TestPlannerWithFileSource:
+    """Tests using actual file sources (not direct_text)."""
+
+    def test_txt_file(self):
+        """Planning from a .txt file."""
+        with tempfile.NamedTemporaryFile(
+            mode="w", suffix=".txt", delete=False, encoding="utf-8"
+        ) as f:
+            f.write("Chapter 1\nHello from file")
+            f.flush()
+            path = Path(f.name)
+
+        try:
+            req = ConversionRequest(source_path=path, voice="M1")
+            plan = build_conversion_plan(req)
+
+            assert len(plan.chapters) >= 1
+            assert "Hello from file" in plan.chapters[0].segments[0].text
+        finally:
+            os.unlink(path)
+
+    def test_txt_file_with_voice_markers(self):
+        """File with voice markers."""
+        with tempfile.NamedTemporaryFile(
+            mode="w", suffix=".txt", delete=False, encoding="utf-8"
+        ) as f:
+            f.write("Start <<VOICE:F1>> End")
+            f.flush()
+            path = Path(f.name)
+
+        try:
+            req = ConversionRequest(source_path=path, voice="M1")
+            plan = build_conversion_plan(req)
+
+            segments = plan.chapters[0].segments
+            assert len(segments) == 2
+        finally:
+            os.unlink(path)
+
+
+class TestPlannerChapters:
+    """Tests for chapter handling in the planner."""
+
+    def test_single_chapter_no_marker(self):
+        """Text without markers becomes a single chapter."""
+        req = ConversionRequest(direct_text="Just some text", voice="M1")
+        plan = build_conversion_plan(req)
+
+        assert len(plan.chapters) == 1
+        assert plan.chapters[0].title == "text"
+
+    def test_chapters_with_marker(self):
+        """Chapter markers create multiple chapters."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Ch A>>\nText A\n<<CHAPTER_MARKER:Ch B>>\nText B",
+            voice="M1",
+        )
+        plan = build_conversion_plan(req)
+
+        assert len(plan.chapters) == 2
+        assert plan.chapters[0].title == "Ch A"
+        assert plan.chapters[1].title == "Ch B"
+
+    def test_chapter_voice_spec(self):
+        """Chapter voice spec should come from request.voice."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Ch 1>>\nText", voice="af_heart"
+        )
+        plan = build_conversion_plan(req)
+
+        assert plan.chapters[0].voice_spec == "af_heart"
+
+    def test_chapters_preserve_order(self):
+        """Chapters should maintain their order."""
+        req = ConversionRequest(
+            direct_text="<<CHAPTER_MARKER:Ch A>>\nText A\n<<CHAPTER_MARKER:Ch B>>\nText B\n<<CHAPTER_MARKER:Ch C>>\nText C",
+            voice="M1",
+        )
+        plan = build_conversion_plan(req)
+
+        titles = [ch.title for ch in plan.chapters]
+        assert titles == ["Ch A", "Ch B", "Ch C"]
+
+
+# ─── Domain-level regression tests ─────────────────────────────────
+
+class TestChapterParsing:
+    """Verify parse_chapters_from_text produces correct chapter structure."""
+
+    def test_single_chapter_no_markers(self):
+        from abogen.domain.text_chapters import parse_chapters_from_text
+        text = "This is a simple text without any chapter markers."
+        chapters = parse_chapters_from_text(text, clean=False)
+        assert len(chapters) == 1
+        assert chapters[0][0]
+        assert "simple text" in chapters[0][1]
+
+    def test_multiple_chapters_by_markers(self):
+        from abogen.domain.text_chapters import parse_chapters_from_text
+        text = """<<CHAPTER_MARKER:Chapter 1>>
+First chapter content.
+
+<<CHAPTER_MARKER:Chapter 2>>
+Second chapter content."""
+        chapters = parse_chapters_from_text(text, clean=False)
+        assert len(chapters) >= 2
+        titles = [ch[0] for ch in chapters]
+        assert "Chapter 1" in titles
+        assert "Chapter 2" in titles
+
+    def test_empty_text(self):
+        from abogen.domain.text_chapters import parse_chapters_from_text
+        chapters = parse_chapters_from_text("", clean=False)
+        assert len(chapters) >= 1
+
+    def test_chapter_content_preserved(self):
+        from abogen.domain.text_chapters import parse_chapters_from_text
+        text = """<<CHAPTER_MARKER:Chapter 1>>
+Hello world this is chapter one.
+
+<<CHAPTER_MARKER:Chapter 2>>
+Goodbye world this is chapter two."""
+        chapters = parse_chapters_from_text(text, clean=False)
+        assert len(chapters) >= 2
+        all_text = " ".join(ch[1] for ch in chapters)
+        assert "Hello world" in all_text
+        assert "Goodbye world" in all_text
+
+    def test_intro_before_first_marker(self):
+        from abogen.domain.text_chapters import parse_chapters_from_text
+        text = """Introduction text here.
+<<CHAPTER_MARKER:Chapter 1>>
+Chapter content."""
+        chapters = parse_chapters_from_text(text, clean=False)
+        assert len(chapters) >= 2
+        assert chapters[0][0] == "Introduction"
+        assert "Introduction text" in chapters[0][1]
+
+
+class TestVoiceMarkerSplitting:
+    """Verify voice marker splitting produces correct segment structure."""
+
+    def test_no_voice_markers(self):
+        from abogen.subtitle_utils import split_text_by_voice_markers
+        text = "Just plain text without any voice markers."
+        segments, last_voice, valid, invalid = split_text_by_voice_markers(text, "M1")
+        assert len(segments) == 1
+        assert segments[0][0] == "M1"
+        assert "plain text" in segments[0][1]
+
+    def test_single_voice_marker(self):
+        from abogen.subtitle_utils import split_text_by_voice_markers
+        text = "<<VOICE:F1>> Hello from female voice."
+        segments, last_voice, valid, invalid = split_text_by_voice_markers(text, "M1")
+        assert len(segments) >= 1
+        all_text = " ".join(seg[1] for seg in segments)
+        assert "Hello from female" in all_text
+
+    def test_voice_marker_preserves_text(self):
+        from abogen.subtitle_utils import split_text_by_voice_markers
+        text = "<<VOICE:F1>> First sentence. <<VOICE:M1>> Second sentence."
+        segments, last_voice, valid, invalid = split_text_by_voice_markers(text, "M1")
+        all_text = " ".join(seg[1] for seg in segments)
+        assert "First sentence" in all_text
+        assert "Second sentence" in all_text
+
+    def test_voice_marker_persistence(self):
+        from abogen.subtitle_utils import split_text_by_voice_markers
+        text = "<<VOICE:F1>> First part."
+        segments, last_voice, valid, invalid = split_text_by_voice_markers(text, "M1")
+        assert last_voice in ("f1", "F1", "M1")
+
+
+class TestTTSContext:
+    """Verify TTSContext bundles normalization parameters correctly."""
+
+    def test_default_context(self):
+        from abogen.domain.normalization import TTSContext
+        ctx = TTSContext()
+        assert ctx.split_pattern
+        assert ctx.pronunciation_rules is None
+        assert ctx.heteronym_rules is None
+        assert ctx.normalization_overrides is None
+        assert ctx.usage_counter == {}
+
+    def test_normalize_passthrough(self):
+        from abogen.domain.normalization import TTSContext
+        ctx = TTSContext()
+        text = "Hello world."
+        result = ctx.normalize(text)
+        assert isinstance(result, str)
+        assert len(result) > 0
+
+    def test_normalize_with_usage_counter(self):
+        from abogen.domain.normalization import TTSContext
+        ctx = TTSContext()
+        ctx.usage_counter["test_token"] = 0
+        result = ctx.normalize("Some text.")
+        assert isinstance(result, str)
+
+
+class TestVoiceResolution:
+    """Verify voice resolution functions produce valid specs."""
+
+    def test_resolve_fallback_voice_spec(self):
+        from abogen.domain.voice_resolution import resolve_fallback_voice_spec
+        spec = resolve_fallback_voice_spec("M1", "M1", ["M1", "F1"])
+        if spec is not None:
+            assert hasattr(spec, "voice_id") or isinstance(spec, str)
+
+    def test_spec_to_voice_ids(self):
+        from abogen.domain.voice_resolution import spec_to_voice_ids
+        ids = spec_to_voice_ids("M1")
+        assert isinstance(ids, set)
+
+    def test_resolve_fallback_with_empty_cache(self):
+        from abogen.domain.voice_resolution import resolve_fallback_voice_spec
+        spec = resolve_fallback_voice_spec("M1", "M1", [])
+
+
+class TestIntroOutro:
+    """Verify intro/outro resolution with various metadata states."""
+
+    def test_resolve_intro_with_metadata(self):
+        from abogen.domain.intro_outro import resolve_intro
+        metadata = {"title": "Test Book", "author": "Test Author"}
+        spec = resolve_intro(metadata, "test.txt", True, "M1", "M1", ["M1"])
+        assert spec is not None
+        assert spec.text
+
+    def test_resolve_intro_disabled(self):
+        from abogen.domain.intro_outro import resolve_intro
+        spec = resolve_intro({}, "test.txt", False, "M1", "M1", ["M1"])
+        assert not spec.enabled
+
+    def test_resolve_intro_no_metadata(self):
+        from abogen.domain.intro_outro import resolve_intro
+        spec = resolve_intro({}, "test.txt", True, "M1", "M1", ["M1"])
+        assert spec is not None
+
+    def test_resolve_outro_with_metadata(self):
+        from abogen.domain.intro_outro import resolve_outro
+        metadata = {"title": "Test Book"}
+        spec = resolve_outro(metadata, "test.txt", True, "M1", "M1", ["M1"])
+        assert spec is not None
+        assert spec.text
+
+    def test_resolve_outro_disabled(self):
+        from abogen.domain.intro_outro import resolve_outro
+        spec = resolve_outro({}, "test.txt", False, "M1", "M1", ["M1"])
+        assert not spec.enabled
+
+
+class TestOutputPaths:
+    """Verify output path resolution produces valid paths."""
+
+    def test_resolve_unique_path(self, tmp_path):
+        from abogen.domain.output_paths import resolve_unique_path
+        (tmp_path / "test.txt").touch()
+        result = resolve_unique_path(
+            str(tmp_path), "test", "txt",
+            allowed_extensions={"txt", "wav"},
+        )
+        assert result
+        assert "test" in result
+
+    def test_resolve_unique_path_no_collision(self, tmp_path):
+        from abogen.domain.output_paths import resolve_unique_path
+        result = resolve_unique_path(str(tmp_path), "unique_name", "txt")
+        assert result
+        assert "unique_name" in result
+
+    def test_sanitize_output_stem(self):
+        from abogen.domain.output_paths import sanitize_output_stem
+        stem = sanitize_output_stem("My Book Title")
+        assert isinstance(stem, str)
+        assert len(stem) > 0
+
+    def test_resolve_output_directory(self, tmp_path):
+        from abogen.domain.output_paths import resolve_output_directory
+        result = resolve_output_directory(
+            save_mode="Save next to input file",
+            stored_path=tmp_path / "test.txt",
+            output_folder=None,
+            desktop_dir=tmp_path,
+            user_output_path=None,
+            user_cache_outputs=tmp_path,
+        )
+        assert result is not None
+        assert isinstance(result, Path)
+
+
+class TestSubtitleGeneration:
+    """Verify subtitle token processing works correctly."""
+
+    def test_process_empty_tokens(self):
+        from abogen.domain.subtitle_generation import process_subtitle_tokens
+        entries = []
+        process_subtitle_tokens(
+            [], entries, 5, "Sentence", "a",
+            use_spacy_segmentation=False,
+            fallback_end_time=10.0,
+        )
+        assert entries == []
+
+    def test_process_sentence_mode(self):
+        from abogen.domain.subtitle_generation import process_subtitle_tokens
+        tokens = [
+            {"start": 0.0, "end": 0.5, "text": "Hello", "whitespace": " "},
+            {"start": 0.5, "end": 1.0, "text": "world", "whitespace": "."},
+        ]
+        entries = []
+        process_subtitle_tokens(
+            tokens, entries, 5, "Sentence", "a",
+            use_spacy_segmentation=False,
+            fallback_end_time=2.0,
+        )
+        assert len(entries) >= 1
+        start, end, text = entries[0]
+        assert start < end
+        assert isinstance(text, str)
+
+    def test_process_line_mode(self):
+        from abogen.domain.subtitle_generation import process_subtitle_tokens
+        tokens = [
+            {"start": 0.0, "end": 0.5, "text": "Hello", "whitespace": " "},
+            {"start": 0.5, "end": 1.0, "text": "world", "whitespace": "\n"},
+            {"start": 1.0, "end": 1.5, "text": "New", "whitespace": " "},
+            {"start": 1.5, "end": 2.0, "text": "line", "whitespace": "."},
+        ]
+        entries = []
+        process_subtitle_tokens(
+            tokens, entries, 5, "Line", "a",
+            use_spacy_segmentation=False,
+            fallback_end_time=3.0,
+        )
+        assert len(entries) >= 1
+
+
+class TestFeatureParity:
+    """Regression tests for features that must work in both UIs."""
+
+    def test_chapter_title_formatting(self):
+        from abogen.domain.chapter_titles import format_spoken_chapter_title
+        title1 = format_spoken_chapter_title("Chapter 1", 1, apply_prefix=True)
+        title2 = format_spoken_chapter_title("Introduction", 1, apply_prefix=True)
+        assert isinstance(title1, str)
+        assert isinstance(title2, str)
+
+    def test_chapter_title_no_auto_prefix(self):
+        from abogen.domain.chapter_titles import format_spoken_chapter_title
+        title = format_spoken_chapter_title("My Custom Title", 1, apply_prefix=False)
+        assert "My Custom Title" in title
+
+    def test_m4b_forces_merge(self):
+        output_format = "m4b"
+        merge_chapters_at_end = False
+        if output_format.lower() == "m4b":
+            merge_chapters_at_end = True
+        assert merge_chapters_at_end is True

tests/test_conversion_request.py

@@ -0,0 +1,286 @@
+"""Regression tests for ConversionRequest building.
+
+These tests verify that both WebUI and PyQt adapters can produce
+a valid ConversionRequest from their respective Job/thread state.
+They serve as a specification for the adapter code that will be
+created in Phase 2/3 of the refactor.
+
+Currently these tests verify the EXISTING behavior by testing the
+domain functions that the adapters will call. After the adapters
+are created, these tests should be updated to test the adapters
+directly.
+"""
+
+import pytest
+from pathlib import Path
+from unittest.mock import MagicMock
+
+from abogen.application.conversion_request import ConversionRequest, ConversionRequestError
+from abogen.domain.enums import Language, OutputFormat, SaveMode, SubtitleFormat, SubtitleMode
+from abogen.domain.normalization import TTSContext
+from abogen.domain.settings_core import settings_defaults
+from abogen.domain.split_pattern import get_split_pattern
+
+
+class TestConversionRequestBasics:
+    """Verify that basic request parameters can be derived from settings."""
+
+    def test_settings_defaults_exist(self):
+        defaults = settings_defaults()
+        assert isinstance(defaults, dict)
+        assert "output_format" in defaults
+        assert "subtitle_format" in defaults
+        assert "save_mode" in defaults
+        assert "use_gpu" in defaults
+        assert "silence_between_chapters" in defaults
+        assert "merge_chapters_at_end" in defaults
+
+    def test_split_pattern_computation(self):
+        pattern = get_split_pattern("a", "Disabled")
+        assert isinstance(pattern, str)
+        assert len(pattern) > 0
+
+    def test_split_pattern_varies_by_subtitle_mode(self):
+        pattern_disabled = get_split_pattern("a", "Disabled")
+        pattern_sentence = get_split_pattern("a", "Sentence")
+        # Different modes should produce different patterns
+        assert isinstance(pattern_disabled, str)
+        assert isinstance(pattern_sentence, str)
+
+
+class TestTTSContextBuilding:
+    """Verify TTSContext can be built from settings parameters."""
+
+    def test_build_context_from_params(self):
+        ctx = TTSContext(
+            split_pattern=r"(?<=[.!?\-])\s+",
+            pronunciation_rules=None,
+            heteronym_rules=None,
+            normalization_overrides=None,
+        )
+        assert ctx.split_pattern
+        assert ctx.normalize("Hello world.") is not None
+
+    def test_build_context_with_compiled_rules(self):
+        from abogen.domain.pronunciation import compile_pronunciation_rules
+        rules = compile_pronunciation_rules([{"pattern": "test", "replacement": "Test"}])
+        ctx = TTSContext(
+            split_pattern=r"\n+",
+            pronunciation_rules=rules,
+        )
+        result = ctx.normalize("test text")
+        assert isinstance(result, str)
+
+    def test_usage_counter_tracking(self):
+        ctx = TTSContext()
+        ctx.usage_counter["token1"] = 0
+        ctx.normalize("Some text with token1")
+        # Usage counter should be passed through (may or may not increment
+        # depending on whether the token matches)
+        assert isinstance(ctx.usage_counter, dict)
+
+
+class TestOutputDirectoryResolution:
+    """Verify output directory can be resolved from parameters."""
+
+    def test_resolve_output_directory(self, tmp_path):
+        from abogen.domain.output_paths import resolve_output_directory
+        result = resolve_output_directory(
+            save_mode="Save next to input file",
+            stored_path=tmp_path / "test.txt",
+            output_folder=None,
+            desktop_dir=tmp_path,
+            user_output_path=None,
+            user_cache_outputs=tmp_path,
+        )
+        assert result is not None
+        assert isinstance(result, Path)
+
+    def test_resolve_output_with_explicit_folder(self, tmp_path):
+        from abogen.domain.output_paths import resolve_output_directory
+        custom_dir = tmp_path / "custom_output"
+        custom_dir.mkdir()
+        result = resolve_output_directory(
+            save_mode="Save to custom folder",
+            stored_path=tmp_path / "test.txt",
+            output_folder=str(custom_dir),
+            desktop_dir=tmp_path,
+            user_output_path=None,
+            user_cache_outputs=tmp_path,
+        )
+        assert result is not None
+
+
+class TestChapterSelection:
+    """Verify chapter selection logic works with various inputs."""
+
+    def test_auto_select_relevant_chapters(self):
+        from abogen.domain.file_type import auto_select_relevant_chapters
+        from abogen.text_extractor import ExtractedChapter
+        chapters = [
+            ExtractedChapter(title="Chapter 1", text="A" * 500),
+            ExtractedChapter(title="Chapter 2", text="B" * 50),
+            ExtractedChapter(title="Chapter 3", text="C" * 600),
+        ]
+        result = auto_select_relevant_chapters(chapters, "txt")
+        # Should filter out short chapters
+        assert len(result.kept) >= 1
+        assert isinstance(result.skipped, list)
+
+    def test_auto_select_all_long_chapters(self):
+        from abogen.domain.file_type import auto_select_relevant_chapters
+        from abogen.text_extractor import ExtractedChapter
+        chapters = [
+            ExtractedChapter(title="Chapter 1", text="A" * 500),
+            ExtractedChapter(title="Chapter 2", text="B" * 500),
+        ]
+        result = auto_select_relevant_chapters(chapters, "txt")
+        assert len(result.kept) == 2
+        assert len(result.skipped) == 0
+
+    def test_metadata_merge(self):
+        from abogen.domain.metadata_merge import merge_metadata
+        base = {"title": "Original Title", "author": "Author A"}
+        overrides = {"title": "New Title"}
+        result = merge_metadata(base, overrides)
+        assert result["title"] == "New Title"
+        assert result["author"] == "Author A"
+
+
+class TestCancellationProtocol:
+    """Verify cancellation mechanism can be implemented as a callback."""
+
+    def test_cancellation_flag_check(self):
+        class FakeJob:
+            def __init__(self):
+                self.cancel_requested = False
+
+        job = FakeJob()
+        check = lambda: job.cancel_requested
+        assert check() is False
+
+        job.cancel_requested = True
+        assert check() is True
+
+    def test_cancellation_exception_pattern(self):
+        """WebUI uses exception-based cancellation."""
+        class JobCancelled(Exception):
+            pass
+
+        def canceller():
+            raise JobCancelled()
+
+        with pytest.raises(JobCancelled):
+            canceller()
+
+
+class TestLoggingProtocol:
+    """Verify logging can be abstracted as a callback."""
+
+    def test_log_callback(self):
+        logs = []
+        def log_fn(msg, level="info"):
+            logs.append((msg, level))
+
+        log_fn("Test message", "info")
+        assert len(logs) == 1
+        assert logs[0] == ("Test message", "info")
+
+    def test_progress_callback(self):
+        progress_calls = []
+        def progress_fn(processed, total, etr):
+            progress_calls.append((processed, total, etr))
+
+        progress_fn(100, 1000, "0:05:00")
+        assert len(progress_calls) == 1
+        assert progress_calls[0] == (100, 1000, "0:05:00")
+
+
+class TestConversionRequestValidation:
+    """Verify __post_init__ validation on ConversionRequest."""
+
+    def test_defaults_are_valid(self):
+        req = ConversionRequest()
+        assert req.max_subtitle_words == 50
+        assert req.speed == 1.0
+        assert req.supertonic_total_steps == 5
+        assert req.output_format == OutputFormat.WAV
+        assert req.subtitle_mode == SubtitleMode.DISABLED
+
+    def test_max_subtitle_words_clamped_below_min(self):
+        req = ConversionRequest(max_subtitle_words=0)
+        assert req.max_subtitle_words == 1
+
+    def test_max_subtitle_words_clamped_above_max(self):
+        req = ConversionRequest(max_subtitle_words=999)
+        assert req.max_subtitle_words == 500
+
+    def test_max_subtitle_words_valid(self):
+        req = ConversionRequest(max_subtitle_words=100)
+        assert req.max_subtitle_words == 100
+
+    def test_speed_clamped_below_min(self):
+        req = ConversionRequest(speed=0.1)
+        assert req.speed == 0.5
+
+    def test_speed_clamped_above_max(self):
+        req = ConversionRequest(speed=10.0)
+        assert req.speed == 3.0
+
+    def test_speed_valid(self):
+        req = ConversionRequest(speed=1.5)
+        assert req.speed == 1.5
+
+    def test_supertonic_steps_clamped_below_min(self):
+        req = ConversionRequest(supertonic_total_steps=0)
+        assert req.supertonic_total_steps == 2
+
+    def test_supertonic_steps_clamped_above_max(self):
+        req = ConversionRequest(supertonic_total_steps=100)
+        assert req.supertonic_total_steps == 15
+
+    def test_silence_between_chapters_clamped(self):
+        req = ConversionRequest(silence_between_chapters=-5.0)
+        assert req.silence_between_chapters == 0.0
+
+    def test_chapter_intro_delay_clamped(self):
+        req = ConversionRequest(chapter_intro_delay=-1.0)
+        assert req.chapter_intro_delay == 0.0
+
+    def test_invalid_chunk_level_raises(self):
+        with pytest.raises(ConversionRequestError, match="chunk_level"):
+            ConversionRequest(chunk_level="invalid")
+
+    def test_invalid_speaker_mode_raises(self):
+        with pytest.raises(ConversionRequestError, match="speaker_mode"):
+            ConversionRequest(speaker_mode="invalid")
+
+    def test_invalid_max_subtitle_words_type_raises(self):
+        with pytest.raises(ConversionRequestError, match="max_subtitle_words"):
+            ConversionRequest(max_subtitle_words="not_a_number")
+
+    def test_invalid_speed_type_raises(self):
+        with pytest.raises(ConversionRequestError, match="speed"):
+            ConversionRequest(speed="fast")
+
+    def test_invalid_silence_type_raises(self):
+        with pytest.raises(ConversionRequestError, match="silence_between_chapters"):
+            ConversionRequest(silence_between_chapters="loud")
+
+    def test_empty_tts_provider_defaults_to_kokoro(self):
+        req = ConversionRequest(tts_provider="")
+        assert req.tts_provider == "kokoro"
+
+    def test_enum_fields_accept_valid_values(self):
+        req = ConversionRequest(
+            language=Language.FR,
+            output_format=OutputFormat.MP3,
+            subtitle_mode=SubtitleMode.SENTENCE,
+            subtitle_format=SubtitleFormat.ASS,
+            save_mode=SaveMode.CUSTOM_FOLDER,
+        )
+        assert req.language == Language.FR
+        assert req.output_format == OutputFormat.MP3
+        assert req.subtitle_mode == SubtitleMode.SENTENCE
+        assert req.subtitle_format == SubtitleFormat.ASS
+        assert req.save_mode == SaveMode.CUSTOM_FOLDER

tests/test_domain_audio_buffer_extras.py

@@ -2,6 +2,7 @@
 
 import numpy as np
 import pytest
+from unittest.mock import patch
 
 from abogen.domain.audio_buffer import fit_audio_to_duration, ffmpeg_time_stretch, SAMPLE_RATE
 
@@ -51,9 +52,25 @@ class TestFfmpegTimeStretch:
     result = ffmpeg_time_stretch(np.array([], dtype="float32"), 2.0, SAMPLE_RATE)
     assert len(result) == 0
 
-    def test_stretch_reduces_duration(self):
+@patch("subprocess.Popen")
+def test_stretch_reduces_duration(mock_popen):
+  # Mock subprocess response
+  mock_proc = mock_popen.return_value
+  mock_proc.returncode = 0
+  mock_proc.communicate.return_value = (b"\x00" * 400, b"")
+  mock_proc.stdout.read.return_value = b"\x00" * 400
+
   audio = np.random.randn(48000).astype("float32")
   result = ffmpeg_time_stretch(audio, 2.0, SAMPLE_RATE)
+
+  # Verify ffmpeg was called with correct args
+  mock_popen.assert_called_once()
+  args = mock_popen.call_args[0][0]
+  assert "ffmpeg" in args[0]
+  assert "-filter:a" in args
+  assert any("atempo=" in arg for arg in args)
+
+  # Verify result has reduced duration and correct dtype
   assert len(result) < len(audio)
   assert len(result) > 0
   assert result.dtype == np.float32

tests/test_domain_pipeline_factory.py

@@ -41,16 +41,26 @@ class TestCreatePipelineForJob:
     def test_kokoro_provider(self, _dev, _reg, mock_create):
         mock_create.return_value = MagicMock()
         result = create_pipeline_for_job("kokoro", "en", use_gpu=False)
-        mock_create.assert_called_once_with("kokoro", lang_code="en", device="cpu")
+        # "en" → fallback to EN_US → kokoro code "a"
+        mock_create.assert_called_once_with("kokoro", lang_code="a", device="cpu")
         assert result is mock_create.return_value
 
+    @patch("abogen.domain.pipeline_factory.create_pipeline")
+    @patch("abogen.domain.pipeline_factory.is_plugin_registered", return_value=True)
+    @patch("abogen.domain.pipeline_factory.resolve_device", return_value="cpu")
+    def test_kokoro_provider_iso_code(self, _dev, _reg, mock_create):
+        mock_create.return_value = MagicMock()
+        result = create_pipeline_for_job("kokoro", "en-GB", use_gpu=False)
+        # "en-GB" → EN_GB → kokoro code "b"
+        mock_create.assert_called_once_with("kokoro", lang_code="b", device="cpu")
+
     @patch("abogen.domain.pipeline_factory.create_pipeline")
     @patch("abogen.domain.pipeline_factory.is_plugin_registered", return_value=False)
     @patch("abogen.domain.pipeline_factory.resolve_device", return_value="cpu")
     def test_unknown_provider_falls_back_to_kokoro(self, _dev, _reg, mock_create):
         mock_create.return_value = MagicMock()
         result = create_pipeline_for_job("unknown_provider", "en", use_gpu=False)
-        mock_create.assert_called_once_with("kokoro", lang_code="en", device="cpu")
+        mock_create.assert_called_once_with("kokoro", lang_code="a", device="cpu")
 
     @patch("abogen.domain.pipeline_factory.create_pipeline")
     @patch("abogen.domain.pipeline_factory.is_plugin_registered", return_value=True)
@@ -58,7 +68,7 @@ class TestCreatePipelineForJob:
     def test_empty_provider_defaults_to_kokoro(self, _dev, _reg, mock_create):
         mock_create.return_value = MagicMock()
         result = create_pipeline_for_job("", "en", use_gpu=False)
-        mock_create.assert_called_once_with("kokoro", lang_code="en", device="cpu")
+        mock_create.assert_called_once_with("kokoro", lang_code="a", device="cpu")
 
     @patch("abogen.domain.pipeline_factory.create_pipeline")
     @patch("abogen.domain.pipeline_factory.is_plugin_registered", return_value=True)
@@ -66,7 +76,7 @@ class TestCreatePipelineForJob:
     def test_none_provider_defaults_to_kokoro(self, _dev, _reg, mock_create):
         mock_create.return_value = MagicMock()
         result = create_pipeline_for_job(None, "en", use_gpu=False)
-        mock_create.assert_called_once_with("kokoro", lang_code="en", device="cpu")
+        mock_create.assert_called_once_with("kokoro", lang_code="a", device="cpu")
 
 
 class TestDisposePipelines:

tests/test_enums.py

@@ -0,0 +1,131 @@
+"""Tests for domain enums — validation, properties, from_str methods."""
+
+import pytest
+from pathlib import Path
+
+from abogen.domain.enums import (
+    InputFormat,
+    Language,
+    OutputFormat,
+    SaveMode,
+    SubtitleFormat,
+    SubtitleMode,
+)
+
+
+class TestSubtitleMode:
+    def test_from_str_case_insensitive(self):
+        assert SubtitleMode.from_str("disabled") == SubtitleMode.DISABLED
+        assert SubtitleMode.from_str("SENTENCE") == SubtitleMode.SENTENCE
+        assert SubtitleMode.from_str("line") == SubtitleMode.LINE
+
+    def test_from_str_strips_whitespace(self):
+        assert SubtitleMode.from_str("  Disabled  ") == SubtitleMode.DISABLED
+
+    def test_from_str_invalid(self):
+        with pytest.raises(ValueError, match="Invalid SubtitleMode"):
+            SubtitleMode.from_str("invalid")
+
+    def test_comparison_with_str(self):
+        assert SubtitleMode.DISABLED == "Disabled"
+        assert SubtitleMode.SENTENCE != "Disabled"
+
+
+class TestOutputFormat:
+    def test_dot_ext(self):
+        assert OutputFormat.WAV.dot_ext == ".wav"
+        assert OutputFormat.M4B.dot_ext == ".m4b"
+
+    def test_is_lossless(self):
+        assert OutputFormat.WAV.is_lossless is True
+        assert OutputFormat.FLAC.is_lossless is True
+        assert OutputFormat.MP3.is_lossless is False
+        assert OutputFormat.M4B.is_lossless is False
+
+    def test_from_str_strips_dot(self):
+        assert OutputFormat.from_str(".wav") == OutputFormat.WAV
+        assert OutputFormat.from_str(".MP3") == OutputFormat.MP3
+
+    def test_from_str_case_insensitive(self):
+        assert OutputFormat.from_str("WAV") == OutputFormat.WAV
+        assert OutputFormat.from_str("opus") == OutputFormat.OPUS
+
+    def test_from_str_invalid(self):
+        with pytest.raises(ValueError, match="Invalid OutputFormat"):
+            OutputFormat.from_str("avi")
+
+
+class TestSaveMode:
+    def test_values(self):
+        assert SaveMode.SAVE_NEXT_TO_INPUT == "save_next_to_input"
+        assert SaveMode.CUSTOM_FOLDER == "custom_folder"
+
+
+class TestSubtitleFormat:
+    def test_dot_ext(self):
+        assert SubtitleFormat.SRT.dot_ext == ".srt"
+        assert SubtitleFormat.ASS.dot_ext == ".ass"
+
+    def test_from_str_strips_dot(self):
+        assert SubtitleFormat.from_str(".srt") == SubtitleFormat.SRT
+        assert SubtitleFormat.from_str(".ASS") == SubtitleFormat.ASS
+
+
+class TestInputFormat:
+    def test_is_book(self):
+        assert InputFormat.EPUB.is_book is True
+        assert InputFormat.PDF.is_book is True
+        assert InputFormat.TXT.is_book is True
+        assert InputFormat.MD.is_book is True
+        assert InputFormat.SRT.is_book is False
+
+    def test_is_subtitle(self):
+        assert InputFormat.SRT.is_subtitle is True
+        assert InputFormat.ASS.is_subtitle is True
+        assert InputFormat.VTT.is_subtitle is True
+        assert InputFormat.EPUB.is_subtitle is False
+
+    def test_from_path(self):
+        assert InputFormat.from_path(Path("book.epub")) == InputFormat.EPUB
+        assert InputFormat.from_path(Path("sub.srt")) == InputFormat.SRT
+        assert InputFormat.from_path(Path("notes.MD")) == InputFormat.MD
+        assert InputFormat.from_path(Path("doc.markdown")) == InputFormat.MD
+
+    def test_from_path_invalid(self):
+        with pytest.raises(ValueError, match="Unsupported input format"):
+            InputFormat.from_path(Path("video.mp4"))
+
+    def test_dot_ext(self):
+        assert InputFormat.EPUB.dot_ext == ".epub"
+        assert InputFormat.SRT.dot_ext == ".srt"
+
+
+class TestLanguage:
+    def test_iso_codes(self):
+        assert Language.EN_US == "en-US"
+        assert Language.EN_GB == "en-GB"
+        assert Language.ZH == "zh"
+        assert Language.JA == "ja"
+
+    def test_display_name(self):
+        assert Language.EN_US.display_name == "American English"
+        assert Language.JA.display_name == "Japanese"
+
+    def test_is_cjk(self):
+        assert Language.ZH.is_cjk is True
+        assert Language.JA.is_cjk is True
+        assert Language.EN_US.is_cjk is False
+
+    def test_supports_subtitle_tokens(self):
+        assert Language.EN_US.supports_subtitle_tokens is True
+        assert Language.EN_GB.supports_subtitle_tokens is True
+        assert Language.ZH.supports_subtitle_tokens is False
+
+    def test_from_str_case_insensitive(self):
+        assert Language.from_str("EN-US") == Language.EN_US
+        assert Language.from_str("en-gb") == Language.EN_GB
+        assert Language.from_str("ZH") == Language.ZH
+
+    def test_from_str_invalid(self):
+        with pytest.raises(ValueError, match="Invalid Language"):
+            Language.from_str("en")

tests/test_import_layering.py

@@ -0,0 +1,221 @@
+"""Import/layering tests for the conversion flow unification.
+
+Verifies that:
+- Application layer does not import from PyQt or WebUI
+- Adapters import from application/domain (not the other way around)
+- All application models are importable without GUI/Flask side effects
+"""
+
+import importlib
+import sys
+from pathlib import Path
+
+import pytest
+
+
+# ─── Application layer imports ─────────────────────────────────────
+
+
+class TestApplicationLayerImports:
+    """Verify application layer has no PyQt/WebUI imports."""
+
+    APPLICATION_DIR = Path(__file__).parent.parent / "abogen" / "application"
+
+    def _get_python_files(self):
+        """Get all Python files in the application directory."""
+        return list(self.APPLICATION_DIR.glob("*.py"))
+
+    def test_no_pyqt_imports(self):
+        """Application layer must not import from abogen.pyqt."""
+        import re
+
+        forbidden = re.compile(r"from\s+abogen\.pyqt|import\s+abogen\.pyqt")
+        violations = []
+
+        for py_file in self._get_python_files():
+            content = py_file.read_text(encoding="utf-8")
+            if forbidden.search(content):
+                violations.append(py_file.name)
+
+        assert not violations, f"Application files import from PyQt: {violations}"
+
+    def test_no_webui_imports(self):
+        """Application layer must not import from abogen.webui."""
+        import re
+
+        forbidden = re.compile(r"from\s+abogen\.webui|import\s+abogen\.webui")
+        violations = []
+
+        for py_file in self._get_python_files():
+            content = py_file.read_text(encoding="utf-8")
+            if forbidden.search(content):
+                violations.append(py_file.name)
+
+        assert not violations, f"Application files import from WebUI: {violations}"
+
+    def test_no_flask_imports(self):
+        """Application layer must not import Flask."""
+        import re
+
+        forbidden = re.compile(r"from\s+flask|import\s+flask")
+        violations = []
+
+        for py_file in self._get_python_files():
+            content = py_file.read_text(encoding="utf-8")
+            if forbidden.search(content):
+                violations.append(py_file.name)
+
+        assert not violations, f"Application files import Flask: {violations}"
+
+    def test_no_qthread_imports(self):
+        """Application layer must not import QThread."""
+        import re
+
+        forbidden = re.compile(r"from\s+PyQt6|import\s+PyQt6")
+        violations = []
+
+        for py_file in self._get_python_files():
+            content = py_file.read_text(encoding="utf-8")
+            if forbidden.search(content):
+                violations.append(py_file.name)
+
+        assert not violations, f"Application files import PyQt6: {violations}"
+
+
+class TestApplicationModelsImportable:
+    """Verify application models are importable without side effects."""
+
+    def test_conversion_request_importable(self):
+        from abogen.application.conversion_request import ConversionRequest
+
+        assert ConversionRequest is not None
+
+    def test_conversion_models_importable(self):
+        from abogen.application.conversion_models import (
+            ChapterPlan,
+            ConversionPlan,
+            IntroOutroSpec,
+            OutputLayout,
+            SegmentPlan,
+        )
+
+        assert all(
+            cls is not None
+            for cls in [ChapterPlan, ConversionPlan, IntroOutroSpec, OutputLayout, SegmentPlan]
+        )
+
+    def test_conversion_result_importable(self):
+        from abogen.application.conversion_result import ConversionError, ConversionResult
+
+        assert ConversionResult is not None
+        assert ConversionError is not None
+
+    def test_conversion_ports_importable(self):
+        from abogen.application.conversion_ports import (
+            AudioSink,
+            ConversionEvents,
+            PipelineProvider,
+            ResolvedVoice,
+            SubtitleWriter,
+            VoiceResolver,
+        )
+
+        assert all(
+            cls is not None
+            for cls in [
+                AudioSink,
+                ConversionEvents,
+                PipelineProvider,
+                ResolvedVoice,
+                SubtitleWriter,
+                VoiceResolver,
+            ]
+        )
+
+    def test_output_layout_service_importable(self):
+        from abogen.application.output_layout_service import (
+            resolve_chapter_path,
+            resolve_merged_path,
+            resolve_output_layout,
+            should_merge_output,
+        )
+
+        assert all(
+            fn is not None
+            for fn in [resolve_chapter_path, resolve_merged_path, resolve_output_layout, should_merge_output]
+        )
+
+    def test_conversion_planner_importable(self):
+        from abogen.application.conversion_planner import build_conversion_plan
+
+        assert build_conversion_plan is not None
+
+    def test_conversion_executor_importable(self):
+        from abogen.application.conversion_executor import execute_conversion
+
+        assert execute_conversion is not None
+
+    def test_conversion_service_importable(self):
+        from abogen.application.conversion_service import run_conversion
+
+        assert run_conversion is not None
+
+
+class TestAdapterImports:
+    """Verify adapters import from application/domain correctly."""
+
+    def test_webui_adapter_imports_application(self):
+        from abogen.webui.conversion_adapter import (
+            WebJobEvents,
+            WebPipelineProvider,
+            WebVoiceResolver,
+            build_conversion_request_from_job,
+        )
+
+        assert all(
+            cls is not None
+            for cls in [
+                WebJobEvents,
+                WebPipelineProvider,
+                WebVoiceResolver,
+                build_conversion_request_from_job,
+            ]
+        )
+
+    def test_pyqt_adapter_imports_application(self):
+        from abogen.pyqt.conversion_adapter import (
+            PyQtEvents,
+            PyQtPipelineProvider,
+            PyQtVoiceResolver,
+            build_conversion_request_from_thread,
+        )
+
+        assert all(
+            cls is not None
+            for cls in [
+                PyQtEvents,
+                PyQtPipelineProvider,
+                PyQtVoiceResolver,
+                build_conversion_request_from_thread,
+            ]
+        )
+
+    def test_webui_adapter_does_not_import_pyqt(self):
+        """WebUI adapter must not import from PyQt."""
+        import re
+
+        adapter_path = Path(__file__).parent.parent / "abogen" / "webui" / "conversion_adapter.py"
+        content = adapter_path.read_text(encoding="utf-8")
+
+        forbidden = re.compile(r"from\s+abogen\.pyqt|import\s+abogen\.pyqt")
+        assert not forbidden.search(content), "WebUI adapter imports from PyQt"
+
+    def test_pyqt_adapter_does_not_import_webui(self):
+        """PyQt adapter must not import from WebUI."""
+        import re
+
+        adapter_path = Path(__file__).parent.parent / "abogen" / "pyqt" / "conversion_adapter.py"
+        content = adapter_path.read_text(encoding="utf-8")
+
+        forbidden = re.compile(r"from\s+abogen\.webui|import\s+abogen\.webui")
+        assert not forbidden.search(content), "PyQt adapter imports from WebUI"

tests/test_split_pattern.py

@@ -12,49 +12,49 @@ from abogen.domain.split_pattern import get_split_pattern
 
 class TestEnglish:
     def test_english_sentence(self):
-        assert get_split_pattern("a", "Sentence") == "\n"
+        assert get_split_pattern("en-US", "Sentence") == "\n"
 
     def test_english_sentence_comma(self):
-        assert get_split_pattern("a", "Sentence + Comma") == "\n"
+        assert get_split_pattern("en-US", "Sentence + Comma") == "\n"
 
     def test_english_line(self):
-        assert get_split_pattern("a", "Line") == "\n"
+        assert get_split_pattern("en-US", "Line") == "\n"
 
     def test_english_disabled(self):
-        assert get_split_pattern("a", "Disabled") == "\n"
+        assert get_split_pattern("en-US", "Disabled") == "\n"
 
-    def test_english_b(self):
+    def test_english_gb(self):
-        assert get_split_pattern("b", "Sentence") == "\n"
+        assert get_split_pattern("en-GB", "Sentence") == "\n"
 
 
 # --- CJK languages ---
 
 class TestCJK:
     def test_chinese_disabled(self):
-        pattern = get_split_pattern("z", "Disabled")
+        pattern = get_split_pattern("zh", "Disabled")
         assert pattern != "\n"
         assert r"\n+" in pattern
 
     def test_chinese_line(self):
-        pattern = get_split_pattern("z", "Line")
+        pattern = get_split_pattern("zh", "Line")
         assert pattern != "\n"
         assert r"\n+" in pattern
 
     def test_chinese_sentence(self):
-        pattern = get_split_pattern("z", "Sentence")
+        pattern = get_split_pattern("zh", "Sentence")
         assert r"\n+" in pattern
 
     def test_chinese_sentence_comma(self):
-        pattern = get_split_pattern("z", "Sentence + Comma")
+        pattern = get_split_pattern("zh", "Sentence + Comma")
         assert r"\n+" in pattern
 
     def test_japanese_disabled(self):
-        pattern = get_split_pattern("j", "Disabled")
+        pattern = get_split_pattern("ja", "Disabled")
         assert pattern != "\n"
         assert r"\n+" in pattern
 
     def test_japanese_sentence(self):
-        pattern = get_split_pattern("j", "Sentence")
+        pattern = get_split_pattern("ja", "Sentence")
         assert r"\n+" in pattern
 
 
@@ -62,18 +62,18 @@ class TestCJK:
 
 class TestOtherLanguages:
     def test_spanish_sentence(self):
-        pattern = get_split_pattern("e", "Sentence")
+        pattern = get_split_pattern("es", "Sentence")
         assert r"\n+" in pattern
 
     def test_spanish_line(self):
-        assert get_split_pattern("e", "Line") == "\n"
+        assert get_split_pattern("es", "Line") == "\n"
 
     def test_spanish_disabled(self):
         # canonical: \n+ for non-CJK Disabled
-        assert get_split_pattern("e", "Disabled") == r"\n+"
+        assert get_split_pattern("es", "Disabled") == r"\n+"
 
     def test_french_sentence_comma(self):
-        pattern = get_split_pattern("f", "Sentence + Comma")
+        pattern = get_split_pattern("fr", "Sentence + Comma")
         assert r"\n+" in pattern
 
     def test_unknown_lang(self):
@@ -85,17 +85,17 @@ class TestOtherLanguages:
 
 class TestPatternStructure:
     def test_sentence_has_lookbehind(self):
-        pattern = get_split_pattern("e", "Sentence")
+        pattern = get_split_pattern("es", "Sentence")
         assert r"(?<=" in pattern
 
     def test_sentence_comma_has_comma_chars(self):
-        pattern = get_split_pattern("e", "Sentence + Comma")
+        pattern = get_split_pattern("es", "Sentence + Comma")
         assert "," in pattern
 
     def test_cjk_spacing_uses_star(self):
-        pattern = get_split_pattern("z", "Sentence")
+        pattern = get_split_pattern("zh", "Sentence")
         assert r"\s*" in pattern
 
     def test_non_cjk_spacing_uses_plus(self):
-        pattern = get_split_pattern("e", "Sentence")
+        pattern = get_split_pattern("es", "Sentence")
         assert r"\s+" in pattern