feat: migrate remaining consumers to new Plugin Architecture

- Add compatibility functions to tts_plugin/compat.py:
  - get_metadata(): returns TTSBackendMetadata with voices
  - is_registered_backend(): checks if plugin is loaded
  - resolve_backend_for_voice(): resolves backend for voice spec
  - get_default_voice(): gets default voice for backend

- Update tts_plugin/__init__.py to export new functions

- Migrate all consumers from old tts_backend_registry:
  - WebUI: conversion_runner, debug_tts_runner, routes/api, routes/utils/*
  - PyQt UI: gui, predownload_gui, voice_formula_gui
  - Voice utilities: voice_cache, voice_formulas, voice_profiles
  - Other: subtitle_utils, utils, predownload_gui (root)

- Update tests to use new plugin architecture

Old architecture remains intact as fallback.

abogen/predownload_gui.py

@@ -22,7 +22,7 @@ from PyQt6.QtWidgets import (
 from PyQt6.QtCore import QThread, pyqtSignal
 
 from abogen.constants import COLORS
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 from abogen.spacy_utils import SPACY_MODELS
 import abogen.hf_tracker
 

abogen/pyqt/gui.py

@@ -86,7 +86,7 @@ from abogen.constants import (
     COLORS,
     SUBTITLE_FORMATS,
 )
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 import threading
 from abogen.pyqt.voice_formula_gui import VoiceFormulaDialog
 from abogen.voice_profiles import load_profiles

abogen/pyqt/predownload_gui.py

@@ -22,7 +22,7 @@ from PyQt6.QtWidgets import (
 from PyQt6.QtCore import QThread, pyqtSignal
 
 from abogen.constants import COLORS
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 from abogen.spacy_utils import SPACY_MODELS
 import abogen.hf_tracker
 

abogen/pyqt/voice_formula_gui.py

@@ -32,7 +32,7 @@ from abogen.constants import (
     LANGUAGE_DESCRIPTIONS,
     COLORS,
 )
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 import re
 import platform
 from abogen.utils import get_resource_path

abogen/subtitle_utils.py

@@ -477,7 +477,7 @@ def validate_voice_name(voice_name):
             - is_valid: True if all voices in the name/formula are valid
             - invalid_voice_name: The first invalid voice found, or None if all valid
     """
-    from abogen.tts_backend_registry import get_metadata
+    from abogen.tts_plugin.compat import get_metadata
 
     # Create case-insensitive lookup set (done once per call)
     voice_lookup_lower = {v.lower() for v in get_metadata("kokoro").voices}
@@ -518,7 +518,7 @@ def split_text_by_voice_markers(text, default_voice):
             - valid_count: Number of valid voice markers processed
             - invalid_count: Number of invalid voice markers skipped
     """
-    from abogen.tts_backend_registry import get_metadata
+    from abogen.tts_plugin.compat import get_metadata
 
     voice_splits = list(_VOICE_MARKER_SEARCH_PATTERN.finditer(text))
 

abogen/tts_plugin/__init__.py

@@ -61,6 +61,10 @@ Usage:
         reset_plugin_manager,
         # Compatibility
         create_backend,
+        get_metadata,
+        is_registered_backend,
+        resolve_backend_for_voice,
+        get_default_voice,
     )
 """
 
@@ -106,7 +110,13 @@ from abogen.tts_plugin.types import (
 
 # Plugin Manager and Compatibility
 from abogen.tts_plugin.plugin_manager import get_plugin_manager, reset_plugin_manager
-from abogen.tts_plugin.compat import create_backend
+from abogen.tts_plugin.compat import (
+    create_backend,
+    get_default_voice,
+    get_metadata,
+    is_registered_backend,
+    resolve_backend_for_voice,
+)
 
 __all__ = [
     # Types
@@ -153,4 +163,8 @@ __all__ = [
     "reset_plugin_manager",
     # Compatibility
     "create_backend",
+    "get_metadata",
+    "is_registered_backend",
+    "resolve_backend_for_voice",
+    "get_default_voice",
 ]

abogen/tts_plugin/compat.py

@@ -135,3 +135,141 @@ def create_backend(backend_id: str, **kwargs: Any) -> Any:
     manager = get_plugin_manager()
     engine = manager.create_engine(backend_id, **kwargs)
     return CompatBackend(engine, **kwargs)
+
+def get_metadata(backend_id: str) -> Any:
+    """Get metadata for a specific backend using the new Plugin Architecture.
+
+    This is a drop-in replacement for the old `get_metadata()` function
+    from `abogen.tts_backend_registry`.
+
+    Args:
+        backend_id: The backend/plugin ID (e.g., "kokoro")
+
+    Returns:
+        TTSBackendMetadata-like object with voices attribute
+
+    Raises:
+        KeyError: If plugin_id is not found
+    """
+    from abogen.tts_backend import TTSBackendMetadata
+
+    manager = get_plugin_manager()
+    plugin_info = manager.get_plugin(backend_id)
+
+    if plugin_info is None:
+        raise KeyError(f"Unknown backend: {backend_id}")
+
+    manifest = plugin_info["manifest"]
+
+    # Import voice lists from plugin engines
+    # This avoids creating an engine just to get the voice list
+    voices: tuple[str, ...] = ()
+    if backend_id == "kokoro":
+        try:
+            from plugins.kokoro.engine import _KOKORO_VOICES
+            voices = _KOKORO_VOICES
+        except ImportError:
+            pass
+    elif backend_id == "supertonic":
+        try:
+            from plugins.supertonic.engine import _SUPERTONIC_VOICES
+            voices = _SUPERTONIC_VOICES
+        except ImportError:
+            pass
+
+    return TTSBackendMetadata(
+        id=manifest.id,
+        name=manifest.name,
+        description=manifest.description,
+        voices=voices,
+    )
+
+
+def is_registered_backend(backend_id: str) -> bool:
+    """Check if a backend is registered using the new Plugin Architecture.
+
+    This is a drop-in replacement for the old `is_registered_backend()` function
+    from `abogen.tts_backend_registry`.
+
+    Args:
+        backend_id: The backend/plugin ID (e.g., "kokoro")
+
+    Returns:
+        True if the plugin is loaded, False otherwise
+    """
+    manager = get_plugin_manager()
+    return manager.has_plugin(backend_id)
+
+
+def resolve_backend_for_voice(
+    spec: str,
+    fallback: str = "kokoro",
+) -> str:
+    """Determine which backend owns the given voice specification.
+
+    This is a drop-in replacement for the old `resolve_backend_for_voice()` function
+    from `abogen.tts_backend_registry`.
+
+    Resolution rules:
+    1. Empty spec -> fallback
+    2. Kokoro formula (contains '*' or '+') -> "kokoro"
+    3. Exact voice ID match against registered plugins -> plugin id
+    4. Unknown voice -> fallback
+
+    Args:
+        spec: Voice specification (e.g., "af_nova", "M1", "af_nova*0.7+am_liam*0.3")
+        fallback: Fallback backend ID if no match is found
+
+    Returns:
+        The backend/plugin ID that owns the voice
+    """
+    raw = str(spec or "").strip()
+    if not raw:
+        return fallback
+
+    # Kokoro formula detection
+    if "*" in raw or "+" in raw:
+        return "kokoro"
+
+    manager = get_plugin_manager()
+    upper = raw.upper()
+
+    # Check each plugin's voices
+    for plugin_info in manager.list_plugins():
+        manifest = plugin_info
+        for voice_source in manifest.engine.voiceSources:
+            if voice_source.type == "list" and isinstance(voice_source.config, dict):
+                try:
+                    engine = manager.create_engine(manifest.id)
+                    if hasattr(engine, "listVoices"):
+                        voice_manifests = engine.listVoices(voice_source.id)
+                        voice_ids = [v.id.upper() for v in voice_manifests]
+                        if upper in voice_ids:
+                            engine.dispose()
+                            return manifest.id
+                    engine.dispose()
+                except Exception:
+                    continue
+
+    return fallback
+
+
+def get_default_voice(backend_id: str, fallback: str = "") -> str:
+    """Return the first voice of a backend, or fallback if none.
+
+    This is a drop-in replacement for the old `get_default_voice()` function
+    from `abogen.tts_backend_registry`.
+
+    Args:
+        backend_id: The backend/plugin ID (e.g., "kokoro")
+        fallback: Fallback voice if no voices are available
+
+    Returns:
+        The first voice ID, or fallback if none
+    """
+    try:
+        metadata = get_metadata(backend_id)
+        voices = metadata.voices
+        return voices[0] if voices else fallback
+    except KeyError:
+        return fallback

abogen/utils.py

@@ -538,7 +538,7 @@ class LoadPipelineThread(Thread):
 
     def run(self):
         try:
-            from abogen.tts_backend_registry import create_backend
+            from abogen.tts_plugin.compat import create_backend
 
             backend = create_backend(
                 "kokoro", lang_code=self.lang_code, device=self.device

abogen/voice_cache.py

@@ -17,7 +17,7 @@ if LocalEntryNotFoundError is None:  # pragma: no cover - fallback for tests
         pass
 
 
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 
 _CACHE_LOCK = threading.Lock()
 _CACHED_VOICES: Set[str] = set()

abogen/voice_formulas.py

@@ -1,7 +1,7 @@
 import re
 from typing import List, Tuple
 
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 
 
 # Calls parsing and loads the voice to gpu or cpu

abogen/voice_profiles.py

@@ -2,7 +2,7 @@ import json
 import os
 from typing import Any, Dict, Iterable, List, Tuple
 
-from abogen.tts_backend_registry import get_metadata, is_registered_backend
+from abogen.tts_plugin.compat import get_metadata, is_registered_backend
 from abogen.utils import get_user_config_path
 
 

abogen/webui/conversion_runner.py

@@ -20,7 +20,7 @@ import numpy as np
 import soundfile as sf
 import static_ffmpeg
 
-from abogen.tts_backend_registry import get_metadata, is_registered_backend, resolve_backend_for_voice
+from abogen.tts_plugin.compat import get_metadata, is_registered_backend, resolve_backend_for_voice
 from abogen.epub3.exporter import build_epub3_package
 from abogen.kokoro_text_normalization import ApostropheConfig, normalize_for_pipeline, HAS_NUM2WORDS
 from abogen.normalization_settings import (
@@ -40,8 +40,7 @@ from abogen.utils import (
     get_user_output_path,
     load_config,
 )
-from abogen.tts_backend_registry import create_backend
-from abogen.tts_backend import TTSBackend
+from abogen.tts_plugin.compat import create_backend
 from abogen.voice_cache import ensure_voice_assets
 from abogen.voice_formulas import extract_voice_ids, get_new_voice
 from abogen.voice_profiles import load_profiles, normalize_profile_entry

abogen/webui/debug_tts_runner.py

@@ -15,7 +15,7 @@ from abogen.normalization_settings import build_apostrophe_config
 from abogen.text_extractor import extract_from_path
 from abogen.voice_cache import ensure_voice_assets
 from abogen.webui.conversion_runner import SAMPLE_RATE, SPLIT_PATTERN, _select_device, _to_float32, _resolve_voice, _spec_to_voice_ids
-from abogen.tts_backend_registry import create_backend
+from abogen.tts_plugin.compat import create_backend
 
 
 _MARKER_RE = re.compile(re.escape(MARKER_PREFIX) + r"(?P<code>[A-Z0-9_]+)" + re.escape(MARKER_SUFFIX))

abogen/webui/routes/api.py

@@ -34,7 +34,7 @@ from abogen.normalization_settings import (
 )
 from abogen.llm_client import list_models, LLMClientError
 from abogen.kokoro_text_normalization import normalize_for_pipeline
-from abogen.tts_backend_registry import is_registered_backend
+from abogen.tts_plugin.compat import is_registered_backend
 from abogen.integrations.audiobookshelf import AudiobookshelfClient, AudiobookshelfConfig
 from abogen.integrations.calibre_opds import (
     CalibreOPDSClient,

abogen/webui/routes/utils/form.py

@@ -7,7 +7,7 @@ from flask.typing import ResponseReturnValue
 
 from abogen.webui.service import PendingJob, JobStatus
 from abogen.webui.routes.utils.service import get_service
-from abogen.tts_backend_registry import is_registered_backend
+from abogen.tts_plugin.compat import is_registered_backend
 from abogen.webui.routes.utils.settings import (
     load_settings,
     coerce_bool,
@@ -33,7 +33,7 @@ from abogen.webui.routes.utils.common import split_profile_spec
 from abogen.utils import calculate_text_length
 from abogen.voice_profiles import serialize_profiles, normalize_profile_entry
 from abogen.chunking import ChunkLevel, build_chunks_for_chapters
-from abogen.tts_backend_registry import get_default_voice
+from abogen.tts_plugin.compat import get_default_voice
 from abogen.speaker_configs import get_config
 from abogen.kokoro_text_normalization import normalize_roman_numeral_titles
 from dataclasses import dataclass

abogen/webui/routes/utils/settings.py

@@ -7,7 +7,7 @@ from abogen.constants import (
     SUBTITLE_FORMATS,
     SUPPORTED_SOUND_FORMATS,
 )
-from abogen.tts_backend_registry import get_default_voice
+from abogen.tts_plugin.compat import get_default_voice
 from abogen.normalization_settings import (
     DEFAULT_LLM_PROMPT,
     environment_llm_defaults,

abogen/webui/routes/utils/voice.py

@@ -18,9 +18,9 @@ from abogen.constants import (
     SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION,
     SAMPLE_VOICE_TEXTS,
 )
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 from abogen.speaker_configs import list_configs
-from abogen.tts_backend_registry import create_backend
+from abogen.tts_plugin.compat import create_backend
 from abogen.webui.conversion_runner import _select_device, _to_float32, SAMPLE_RATE, SPLIT_PATTERN
 
 _preview_pipeline_lock = threading.RLock()

tests/test_conversion_voice_resolution.py

@@ -1,7 +1,7 @@
 from types import SimpleNamespace
 from typing import cast
 
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 from abogen.webui.conversion_runner import (
     _chapter_voice_spec,
     _chunk_voice_spec,

tests/test_voice_cache.py

@@ -3,7 +3,7 @@ from typing import cast
 
 import pytest
 
-from abogen.tts_backend_registry import get_metadata
+from abogen.tts_plugin.compat import get_metadata
 from abogen.voice_cache import (
     LocalEntryNotFoundError,
     _CACHED_VOICES,