refactor(webui): rename preview.py to synthesize.py and remove dead code

- Rename abogen/webui/routes/utils/preview.py → synthesize.py
  The file contains the core TTS synthesis pipeline (generate_preview_audio,
  synthesize_preview), not just preview logic. Name now matches responsibility.
- Remove dead code from voice.py: get_preview_pipeline(), synthesize_audio_from_normalized(),
  _preview_pipeline_lock, _preview_pipelines, and unused imports (threading, numpy,
  create_pipeline, get_new_voice, _select_device, _to_float32, SAMPLE_RATE, SPLIT_PATTERN).
  These were never called — identical logic lives in synthesize.py.
- Update imports in api.py, voices.py, and test_preview_applies_manual_overrides.py
- 7 new tests in test_synthesize_module.py enforce file naming and import rules
- 7 tests in test_domain_imports.py updated for renamed module

abogen/webui/routes/api.py

@@ -25,7 +25,7 @@ from abogen.voice_profiles import (
     normalize_profile_entry,
 )
 from abogen.webui.routes.utils.common import split_profile_spec
-from abogen.webui.routes.utils.preview import synthesize_preview, generate_preview_audio
+from abogen.webui.routes.utils.synthesize import synthesize_preview, generate_preview_audio
 from abogen.webui.routes.utils.voice import formula_from_profile
 from abogen.normalization_settings import (
     build_llm_configuration,

abogen/webui/routes/utils/voice.py

@@ -1,6 +1,4 @@
-import threading
 from typing import Any, Dict, Iterable, List, Mapping, Optional, Tuple, cast
-import numpy as np
 
 from abogen.speaker_configs import slugify_label
 from abogen.speaker_analysis import analyze_speakers
@@ -10,7 +8,7 @@ from abogen.voice_profiles import (
     load_profiles,
     serialize_profiles,
 )
-from abogen.voice_formulas import get_new_voice, parse_formula_terms
+from abogen.voice_formulas import parse_formula_terms
 from abogen.constants import (
     LANGUAGE_DESCRIPTIONS,
     SUBTITLE_FORMATS,
@@ -20,14 +18,7 @@ from abogen.constants import (
 )
 from abogen.tts_plugin.utils import get_voices
 from abogen.speaker_configs import list_configs
-from abogen.tts_plugin.utils import create_pipeline
-from abogen.domain.device import select_device as _select_device
-from abogen.domain.audio_helpers import to_float32 as _to_float32, SAMPLE_RATE
 
-SPLIT_PATTERN = r"\n+"
-
-_preview_pipeline_lock = threading.RLock()
-_preview_pipelines: Dict[Tuple[str, str], Any] = {}
 
 def build_narrator_roster(
     voice: str,
@@ -736,76 +727,3 @@ def pairs_to_formula(pairs: Iterable[Tuple[str, float]]) -> Optional[str]:
 
 def profiles_payload() -> Dict[str, Any]:
     return {"profiles": serialize_profiles()}
-
-
-def get_preview_pipeline(language: str, device: str):
-    key = (language, device)
-    with _preview_pipeline_lock:
-        pipeline = _preview_pipelines.get(key)
-        if pipeline is not None:
-            return pipeline
-        pipeline = create_pipeline("kokoro", lang_code=language, device=device)
-        _preview_pipelines[key] = pipeline
-        return pipeline
-
-
-def synthesize_audio_from_normalized(
-    *,
-    normalized_text: str,
-    voice_spec: str,
-    language: str,
-    speed: float,
-    use_gpu: bool,
-    max_seconds: float,
-) -> np.ndarray:
-    if not normalized_text.strip():
-        raise ValueError("Preview text is required")
-
-    device = "cpu"
-    if use_gpu:
-        try:
-            device = _select_device()
-        except Exception:
-            device = "cpu"
-            use_gpu = False
-
-    pipeline = get_preview_pipeline(language, device)
-    if pipeline is None:
-        raise RuntimeError("Preview pipeline is unavailable")
-
-    voice_choice: Any = voice_spec
-    if voice_spec and "*" in voice_spec:
-        voice_choice = get_new_voice(pipeline, voice_spec, use_gpu)
-
-    segments = pipeline(
-        normalized_text,
-        voice=voice_choice,
-        speed=speed,
-        split_pattern=SPLIT_PATTERN,
-    )
-
-    audio_chunks: List[np.ndarray] = []
-    accumulated = 0
-    max_samples = int(max(1.0, max_seconds) * SAMPLE_RATE)
-
-    for segment in segments:
-        graphemes = getattr(segment, "graphemes", "").strip()
-        if not graphemes:
-            continue
-        audio = _to_float32(getattr(segment, "audio", None))
-        if audio.size == 0:
-            continue
-        remaining = max_samples - accumulated
-        if remaining <= 0:
-            break
-        if audio.shape[0] > remaining:
-            audio = audio[:remaining]
-        audio_chunks.append(audio)
-        accumulated += audio.shape[0]
-        if accumulated >= max_samples:
-            break
-
-    if not audio_chunks:
-        raise RuntimeError("Preview could not be generated")
-
-    return np.concatenate(audio_chunks)

abogen/webui/routes/voices.py

@@ -9,7 +9,7 @@ from abogen.webui.routes.utils.voice import (
     parse_voice_formula,
 )
 from abogen.webui.routes.utils.settings import load_settings, coerce_bool
-from abogen.webui.routes.utils.preview import synthesize_preview
+from abogen.webui.routes.utils.synthesize import synthesize_preview
 from abogen.speaker_configs import (
     list_configs,
     get_config,