path: root/app/converter/clients/audiocpp.py

"""Client for the audio.cpp audiocpp_server (native ggml TTS families)."""

import json
import logging
import shutil
import tempfile
import urllib.error
import urllib.parse
import urllib.request
from pathlib import Path
from typing import Any, Dict, List, Optional, Set

from .. import config
from ..audio import concat_audio_files
from ..chunking import split_into_chunks
from .base import (BaseTTSClient, ConversionCancelled,
                   NonRetryableTTSError, resolve_request_seed)
from .languages import LANGUAGE_ISO_CODES, normalize_language
from .speakers import is_builtin_speaker, speaker_display_name_for

logger = logging.getLogger(__name__)

# How the "language" request field is expressed by a family.
AUDIOCPP_LANG_DISPLAY = "display"  # Qwen display names, e.g. "English"
AUDIOCPP_LANG_ISO = "iso"          # ISO 639-1 codes, e.g. "en"
AUDIOCPP_LANG_OMIT = "omit"        # no language field; the model detects it

# The Qwen3-TTS family. Unlike every other family (one model type each),
# qwen3_tts hosts several model *types* under one family id, distinguished
# only by the server entry's id/task: the CustomVoice model (built-in
# speakers, e.g. Vivian/Ryan), the Base model (voice cloning via a
# server-side preset), and the VoiceDesign model (task "vdes"). The
# per-entry voice capability below (audiocpp_entry_voice_capability)
# resolves which is which, driving both the Convert form (which voice
# list to show) and the converter's mode selection.
AUDIOCPP_FAMILY_QWEN3_TTS = "qwen3_tts"

# Server model entry tasks this client can synthesize audiobooks with,
# taken from GET /v1/models (the "task" field of each entry; a missing task
# is treated as "tts" — a harmless generic default). "vdes" entries are
# voice design models: the voice is described with --instructions instead
# of coming from a speaker or a reference clip. Entries with any other task
# (asr, vc, diar, ...) are rejected at connect time with a hint to pick a
# synthesis entry.
AUDIOCPP_TASK_TTS = "tts"
AUDIOCPP_TASK_VDES = "vdes"
AUDIOCPP_SYNTHESIS_TASKS = (AUDIOCPP_TASK_TTS, "clon", AUDIOCPP_TASK_VDES)

# The voice capability of a server model entry — how its voice is supplied.
# Resolved per entry from (family, task, id) by
# audiocpp_entry_voice_capability; drives both the Convert form (which
# voice list to show) and the converter (speaker vs preset vs design mode).
# Most families are clone-only; only the Qwen3-TTS CustomVoice entry has
# built-in speakers, and only VoiceDesign entries take a description.
AUDIOCPP_VOICE_SPEAKER = "speaker"  # built-in speaker name (Qwen CustomVoice)
AUDIOCPP_VOICE_CLONE = "clone"      # server-side preset / voice_dir (Base, others)
AUDIOCPP_VOICE_DESIGN = "design"    # voice described by --instructions (vdes)

# HTTP error body fragments identifying deterministic request-configuration
# problems: the identical request will fail on every retry, so the chunk
# loop must give up immediately instead of burning its attempt budget.
# Matched case-insensitively against the server's error message; the
# fragments come from audio.cpp itself, so they hold for every hosted
# family (none are model-specific).
AUDIOCPP_NON_RETRYABLE_ERRORS = (
    # Cloning without the reference transcript (Qwen3-TTS Base ICL mode):
    # the server-side voice has reference audio but no transcript for it.
    "requires reference text",
    # The server cannot resolve a model contract for the family (its own
    # hint text about model_specs/--model-spec-override follows the fragment).
    "model contract spec not found for family",
    "does not embed an audio.cpp model spec",
    "embeds a legacy model spec",
    # The request named a model the server does not host.
    "unknown model id",
    # The model package on disk is incomplete (a companion file the family
    # spec requires — a tokenizer table, a codec — is not where the spec
    # looks for it) or ambiguous (several GGUFs, none named as the weights).
    # Re-downloading the model package fixes these; retrying cannot.
    "missing model package file",
    "missing model root",
    "model directory contains",
    # A companion model directory (e.g. MioTTS's MioCodec) is not installed
    # next to the model.
    "model path does not exist",
    # The hosted session kind cannot synthesize from text at all.
    "supports only speech-to-speech",
    # The request's voice never resolves to reference audio (families
    # without packaged speakers, e.g. Vevo2, need actual audio).
    "requires target_voice",
    # The prompt is not the script format the family requires (see the
    # VibeVoice profile, which formats it client-side).
    "has no valid speaker",
    # The reference voice's audio is longer than the model's encoder
    # capacity (e.g. VoxCPM1/2 AudioVAE): trim the voice's reference wav.
    "sample capacity exceeded",
    # VRAM/graph allocation failures. In the sequential runs this client
    # drives (models unloaded between books) the memory picture does not
    # change between attempts, so a failure here repeats identically.
    "failed to allocate",
    "allocation failed",
)
_REFERENCE_TEXT_FRAGMENT = AUDIOCPP_NON_RETRYABLE_ERRORS[0]

# HTTP error body fragments identifying a model family whose server
# implementation rejects the hosting task of its entry (e.g. Chatterbox
# hosted with task "tts"): the session is created per server.json task,
# so every request fails identically until the entry is re-hosted with
# task "clon" and the server restarted.
AUDIOCPP_CLONE_ONLY_ERRORS = (
    "supports voicecloning and voiceconversion",  # Chatterbox
    "supports the voicecloning task",             # Confucius4-TTS
    "only supports offline voice cloning",        # Echo-TTS
)

# Deterministic failures whose one-line server message is not actionable
# on its own: FRAGMENT -> guidance appended to the "not retryable" error.
# Matched like AUDIOCPP_NON_RETRYABLE_ERRORS (case-insensitive, against the
# server's inner error message); the pairs are checked before the generic
# non-retryable branch so the hint replaces the bare message.
AUDIOCPP_HINTED_ERRORS = (
    # Vevo2 (families without packaged speakers): the voice resolved to a
    # speaker name without reference audio, so there is nothing to clone.
    ("requires target_voice",
     "The selected voice resolved to a name without reference audio: "
     "point this model entry's voice at actual audio (a voice preset "
     "with a reference wav, or the wav in the server's voice directory) "
     "and retry."),
    # VoxCPM1/2: the reference voice is longer than the AudioVAE encoder
    # accepts, so every request cloning it fails the same way.
    ("sample capacity exceeded",
     "The voice's reference audio is longer than this model's encoder "
     "accepts: trim the voice's reference wav in the voices folder and "
     "re-run Configure Backends → audio.cpp so the server picks it up."),
    # An s2s-only family (e.g. PersonaPlex) hosted for generation: no
    # hosting of the entry makes it narrate text.
    ("supports only speech-to-speech",
     "This model is speech-to-speech, not TTS: it has no text-to-speech "
     "task and cannot generate audiobooks. Consider deleting the model "
     "from the server configuration (re-run Configure Backends → "
     "audio.cpp and unselect it)."),
)

# Families whose audio.cpp implementation only synthesizes by cloning a
# reference voice: their session rejects plain TTS regardless of how the
# entry is hosted. chatterbox's own model spec wrongly lists "tts" among
# its tasks (the binary throws "Chatterbox supports VoiceCloning and
# VoiceConversion"), so the set is explicit knowledge here rather than
# something read from the specs.
AUDIOCPP_CLONE_ONLY_FAMILIES = frozenset(
    {"chatterbox", "confucius4_tts", "echo_tts"})

# How a family's voice is supplied — resolved per family from the local
# audio.cpp checkout's model_specs (see audiocpp_family_voice_policy):
AUDIOCPP_VOICE_REQUIRED = "required"  # clone-only: a reference voice is mandatory
AUDIOCPP_VOICE_OPTIONAL = "optional"  # tts + clone: blank voice means plain TTS
AUDIOCPP_VOICE_NONE = "none"          # pure TTS: no cloning, no voice at all

# Spec cache (family -> parsed spec dict, or None for unknown). The form
# consults the policy and capability tags on every menu render, so each
# family's spec is read at most once per process.
_FAMILY_SPECS: Dict[str, Optional[dict]] = {}


def _family_spec(family: str) -> Optional[dict]:
    """FAMILY's parsed model spec from the local audio.cpp checkout.

    Reads ``<checkout>/model_specs/<family>.json`` (the checkout the setup
    wizard manages, which also ships the specs for remote servers), or
    None when the checkout is missing, the family is not described, or the
    spec is unparsable. Results are cached per process.
    """
    if family in _FAMILY_SPECS:
        return _FAMILY_SPECS[family]
    spec: Optional[dict] = None
    try:
        # Imported lazily: backends.audiocpp imports this package (its
        # voices module), so a module-level import would cycle.
        from backends.audiocpp.build import find_local_checkout
        checkout = find_local_checkout()
    except Exception:  # noqa: BLE001 - best effort: no specs, no policy
        checkout = None
    if checkout is not None:
        try:
            parsed = json.loads((checkout / "model_specs" / f"{family}.json")
                                .read_text(encoding="utf-8"))
        except (OSError, ValueError):
            parsed = None
        if isinstance(parsed, dict):
            spec = parsed
    _FAMILY_SPECS[family] = spec
    return spec


def audiocpp_family_spec_tasks(family: str) -> Optional[Set[str]]:
    """FAMILY's task set from the local audio.cpp checkout's model_specs.

    Returns the spec's "tasks" list as a set, or None when the family is
    not described (see _family_spec).
    """
    spec = _family_spec(family)
    if spec is None or not isinstance(spec.get("tasks"), list):
        return None
    return {str(task) for task in spec["tasks"]}


def audiocpp_entry_supports_design(family: str, task: str,
                                   model_id: str) -> bool:
    """Whether a server model entry can design a voice from a description.

    True for task-"vdes" entries (the model *is* a voice-design model) and
    for entries of families whose spec advertises a design task — those
    families design on the regular entry from the request's instructions
    text (e.g. OmniVoice, VoxCPM2). Qwen3-TTS is the exception: its
    design support lives only in a separate VoiceDesign model entry (also
    task "vdes"), while its Base/CustomVoice entries cannot design. Model
    IDs play no role today but stay in the signature for parity with
    audiocpp_entry_voice_capability. Unknown families (no local specs)
    conservatively report no design support.
    """
    if task == AUDIOCPP_TASK_VDES:
        return True
    if family == AUDIOCPP_FAMILY_QWEN3_TTS:
        return False
    spec = _family_spec(family)
    if spec is None:
        return False
    design_markers = {"design", AUDIOCPP_TASK_VDES}
    tasks = audiocpp_family_spec_tasks(family)
    if tasks and tasks & design_markers:
        return True
    capabilities = spec.get("capabilities")
    return isinstance(capabilities, dict) \
        and bool(set(map(str, capabilities)) & design_markers)


def audiocpp_family_voice_policy(family: str) -> str:
    """How a family's voice is supplied — required, optional, or none.

    Pure-TTS families (spec tasks without "clone") synthesize with no
    voice at all; mixed families (tts + clone) may run without one (plain
    TTS) or clone a reference; clone-only families — the explicit
    AUDIOCPP_CLONE_ONLY_FAMILIES set, which also repairs specs that
    wrongly claim "tts" — always need a reference voice. Unknown families
    (no local specs) keep the conservative clone-only default the client
    has always applied.
    """
    if family == AUDIOCPP_FAMILY_QWEN3_TTS \
            or family in AUDIOCPP_CLONE_ONLY_FAMILIES:
        # Qwen3-TTS is entry-typed (speaker/clone/design capability per
        # model id), so the family policy stays out of its way.
        return AUDIOCPP_VOICE_REQUIRED
    tasks = audiocpp_family_spec_tasks(family)
    if not tasks:
        return AUDIOCPP_VOICE_REQUIRED
    if "clone" not in tasks:
        return AUDIOCPP_VOICE_NONE
    if "tts" not in tasks:
        return AUDIOCPP_VOICE_REQUIRED
    return AUDIOCPP_VOICE_OPTIONAL


def audiocpp_family_narrates(family: str) -> Optional[bool]:
    """Whether FAMILY can synthesize narration from text at all.

    Resolved from the family spec's task set: narration needs one of the
    text-synthesis tasks ("tts" plain, "clone" reference-voice, "vdes"
    described-voice). False marks families whose sessions only ever
    transform audio (e.g. PersonaPlex, task "s2s" — its entries fail every
    request with "supports only speech-to-speech sessions"), which the
    Generate form's "All" pick therefore skips. None for families the
    local specs do not describe — conservatively treated as capable, so
    an unknown family is never silently hidden from the menu.
    """
    tasks = audiocpp_family_spec_tasks(family)
    if tasks is None:
        return None
    return bool(tasks & {AUDIOCPP_TASK_TTS, "clone", AUDIOCPP_TASK_VDES})


def _server_error_message(detail: str) -> str:
    """The server's error message from an HTTP error body, else the body.

    The speech endpoint wraps failures as {"error": {"message": ...}};
    the inner message is what matches AUDIOCPP_NON_RETRYABLE_ERRORS and
    what the user should see. Unparseable bodies are returned as-is.
    """
    try:
        payload = json.loads(detail)
    except ValueError:
        return detail
    if isinstance(payload, dict):
        error = payload.get("error")
        if isinstance(error, dict) and isinstance(error.get("message"), str):
            return error["message"]
        if isinstance(error, str):
            return error
    return detail


def _reference_text_error(voice: Optional[str], server_message: str) -> str:
    """Actionable message for the missing-reference-transcript failure.

    The server resolved the requested voice to reference audio but has no
    transcript for it, so its ICL voice-clone path rejects every request.
    The fix is server-side data, not a client retry: prompt_text (or the
    voice preset's reference_text) supplies it, read per request, so no
    server restart is needed. x_vector_only_mode is the transcript-free
    escape hatch, at the cost of speaker similarity.
    """
    name = f"'{voice}'" if voice else "the requested voice"
    return (
        f"The audio.cpp server cannot clone voice {name}: its reference "
        "audio has no transcript, and this model family's voice cloning "
        f"requires one ({server_message}). Add the transcript to the "
        "prompt_text file in the server's voice directory (one "
        "'<voice>|<transcript>' line per voice) or set reference_text on "
        "the voice preset in server.json; the server reads it per request, "
        "no restart needed. Re-running the audio.cpp setup re-transcribes "
        "the reference wavs with whisper. Alternatively rerun with "
        "--option x_vector_only_mode=true to clone from the speaker "
        "embedding alone (no transcript needed; lower similarity)."
    )


def audiocpp_request_error(status: int, detail: str,
                           voice: Optional[str] = None) -> Exception:
    """The exception for a failed audio.cpp speech request.

    Deterministic request-configuration errors (a fragment in
    AUDIOCPP_NON_RETRYABLE_ERRORS) become NonRetryableTTSError so the
    chunk retry loop skips attempts that cannot succeed; clone-only
    hosting errors (AUDIOCPP_CLONE_ONLY_ERRORS) also carry the re-host
    hint, hinted errors (AUDIOCPP_HINTED_ERRORS) their per-fragment
    guidance; everything else returns the plain RuntimeError the retry
    loop has always retried.
    """
    message = _server_error_message(detail)
    lowered = message.lower()
    if _REFERENCE_TEXT_FRAGMENT in lowered:
        return NonRetryableTTSError(
            _reference_text_error(voice, message))
    if any(fragment in lowered for fragment in AUDIOCPP_CLONE_ONLY_ERRORS):
        return NonRetryableTTSError(
            f"audio.cpp server returned HTTP {status} (not retryable): "
            f"{message}. This model family only synthesizes by cloning a "
            "reference voice, so its server entry must be hosted with task "
            '"clon" — re-run Configure Backends → audio.cpp (or edit '
            "server.json) and restart the server.")
    for fragment, hint in AUDIOCPP_HINTED_ERRORS:
        if fragment in lowered:
            return NonRetryableTTSError(
                f"audio.cpp server returned HTTP {status} (not retryable): "
                f"{message}. {hint}")
    if any(fragment in lowered for fragment in AUDIOCPP_NON_RETRYABLE_ERRORS):
        return NonRetryableTTSError(
            f"audio.cpp server returned HTTP {status} (not retryable): "
            f"{message}")
    return RuntimeError(f"audio.cpp server returned HTTP {status}: {detail}")


class AudioCppFamilyProfile:
    """Request conventions of one audio.cpp model family.

    Language style, whether the family reads a style/instruction prompt,
    and how the request text is formatted; these are family-level (every
    entry of a family shares them). Whether a *specific entry* has
    built-in speakers is an entry-level concern, decided by
    audiocpp_entry_voice_capability, not this profile.
    """

    def __init__(self, language_style: str = AUDIOCPP_LANG_OMIT,
                 sends_instructions: bool = False,
                 script_prefix: Optional[str] = None):
        self.language_style = language_style
        self.sends_instructions = sends_instructions
        # SCRIPT_PREFIX, when set, formats every request's text as one
        # "<prefix>: text" script line (audiocpp_script_input): the
        # family's server implementation parses the prompt as a
        # speaker-script and silently drops unprefixed lines (VibeVoice).
        self.script_prefix = script_prefix


# Generic profile for families not listed in AUDIOCPP_FAMILY_PROFILES:
# clone-only, no style instructions, and no language field (the model
# detects the language itself). Describes higgs_audio_tts, voxcpm2,
# fish_audio, dots_tts, dramabox, omnivoice, outetts, glm_tts, miotts,
# moss_tts_*, pocket_tts, ... as well as families added to
# audio.cpp after this table was written.
AUDIOCPP_DEFAULT_FAMILY_PROFILE = AudioCppFamilyProfile()

AUDIOCPP_FAMILY_PROFILES = {
    AUDIOCPP_FAMILY_QWEN3_TTS: AudioCppFamilyProfile(
        language_style=AUDIOCPP_LANG_DISPLAY,
        sends_instructions=True,
    ),
    # Families whose language option takes a code (e.g. "en") instead of
    # a Qwen display name; otherwise clone-only like the default profile.
    "chatterbox": AudioCppFamilyProfile(language_style=AUDIOCPP_LANG_ISO),
    "confucius4_tts": AudioCppFamilyProfile(language_style=AUDIOCPP_LANG_ISO),
    "index_tts2": AudioCppFamilyProfile(language_style=AUDIOCPP_LANG_ISO),
    "magpie_tts": AudioCppFamilyProfile(language_style=AUDIOCPP_LANG_ISO),
    "supertonic": AudioCppFamilyProfile(language_style=AUDIOCPP_LANG_ISO),
    # VibeVoice parses its prompt as a multi-speaker script: every line
    # must read "Speaker N: text" and unprefixed lines are dropped, so the
    # client flattens each request into one Speaker-1 line (the server
    # renormalizes the lowest speaker id to zero — the cloned reference).
    "vibevoice": AudioCppFamilyProfile(script_prefix="Speaker 1"),
}


def audiocpp_script_input(prefix: str, text: str) -> str:
    """TEXT formatted as one "<PREFIX>: text" script line.

    Script-parsed families (VibeVoice) read the prompt line by line and
    silently drop every line without a "Speaker N:" prefix, so the request
    text — which may contain paragraph breaks — is flattened to a single
    line and prefixed. The server renormalizes the lowest speaker id it
    finds to zero (the cloned reference voice), so "Speaker 1" is the
    right prefix for single-narrator audiobook chunks.
    """
    return f"{prefix}: {' '.join(text.split())}"


def audiocpp_entry_voice_capability(family: str, task: str,
                                    model_id: str) -> str:
    """How a server model entry's voice is supplied — speaker/clone/design.

    Resolved from the entry's family, task and id — the same {id, family,
    task} triple GET /v1/models reports, so it works for local server.json
    entries and remote live-queried entries alike. Qwen3-TTS is the one
    family hosting several model *types* under one family id: the
    CustomVoice model (id contains "customvoice") has built-in speakers, the
    Base model and any other entry are clone-only, and VoiceDesign entries
    (task "vdes") take a description. Every other family is clone-only.
    """
    if task == AUDIOCPP_TASK_VDES:
        return AUDIOCPP_VOICE_DESIGN
    if family == AUDIOCPP_FAMILY_QWEN3_TTS \
            and "customvoice" in (model_id or "").lower():
        return AUDIOCPP_VOICE_SPEAKER
    return AUDIOCPP_VOICE_CLONE


class AudioCppTTSClient(BaseTTSClient):
    """Generates audio chunks through an audio.cpp audiocpp_server.

    Talks to the OpenAI-style HTTP API of audiocpp_server, which hosts TTS
    model families through a native ggml runtime (GGUF weights, no Python
    serving stack). The server API is family-agnostic; the family and task
    of the configured model entry are read from GET /v1/models at startup
    and adapt the request payload (language field style, style instructions)
    through AUDIOCPP_FAMILY_PROFILES. The entry's voice capability
    (audiocpp_entry_voice_capability: speaker / clone / design) decides how
    its voice is supplied; all three are resolved server-side from the
    request's "voice"/"instructions" fields:

    - Speaker mode (--voice with a built-in speaker name): Qwen3-TTS
      CustomVoice only. A built-in speaker name (e.g. "Vivian") is passed
      through. The selected entry must be the CustomVoice model (capability
      == speaker); a speaker name on a non-speaker entry is treated as a
      server-side preset instead.
    - Preset mode (--voice NAME): a voice configured on the server
      (``voice_presets`` or ``voice_dir`` in its config, e.g. a cloning
      reference). The name is validated against GET /v1/audio/voices at
      startup because an unresolvable name would silently fall back to
      plain TTS on a clone-based model instead of failing. To clone on a
      Qwen3-TTS setup, select the Base model entry with --model and pass
      a preset voice.
    - Voice design (task "vdes" entries, e.g. Qwen3-TTS VoiceDesign): the
      voice is described in natural language through ``instructions``,
      which is required and sent with every request (no ``voice`` field).
      A constant per-run seed keeps the designed voice consistent across
      chunk boundaries.
    - Plain TTS (families whose spec has no "clone" task, and mixed
      tts+clone families used without a voice): no reference voice is
      needed, so no ``voice`` field is sent. Clone-only families (e.g.
      Chatterbox) always require ``--voice``.

    The entry's capability decides how an explicit --voice is read: on a
    speaker-capable entry a name that matches a built-in speaker selects
    speaker mode, and every other name is a server-side preset. The
    entry's capability picks the mode: design entries require
    --instructions; speaker entries require --voice naming a built-in
    CustomVoice speaker; clone entries (the Base model, and every other
    family) require --voice with a server-side preset — all fail fast
    with a hint instead of silently synthesizing with a random default
    voice.

    ``instructions`` also works on non-design entries, where it acts as a
    generic style/delivery instruction (voice control): families that read
    it (OmniVoice, Qwen3-TTS CustomVoice, ...) shape the voice or delivery
    accordingly, and others ignore it. On instruction-conditioned families
    without built-in speakers it may replace --voice entirely (the
    instruction defines the voice). Extra request options (``--option
    KEY=VALUE``, e.g. emotion, voice_id, speed) are forwarded verbatim in
    the request's "options" object, which is the server's generic
    pass-through for per-model controls.

    Chunking: text is split client-side into sub-requests of at most
    config.CHUNK_SIZE words each; each sub-request returns a complete
    WAV file and the parts are concatenated with the same lossless path
    used for the Qwen client.
    """

    def __init__(self, chunks_dir: Path,
                 voice: Optional[str] = None, language: Optional[str] = None,
                 api_url: Optional[str] = None,
                 model_id: Optional[str] = None,
                 instructions: Optional[str] = None,
                 request_options: Optional[Dict[str, str]] = None,
                 quiet: bool = False,
                 unload_models: Optional[bool] = None):
        super().__init__(chunks_dir, quiet=quiet)
        self.api_url = (api_url or config.AUDIOCPP_API_URL).rstrip("/")
        # Per-run model selection: the --model CLI flag (or the Generate
        # form's Model pick). An empty value is resolved at connect time
        # when the server hosts exactly one entry, so single-model servers
        # don't require --model.
        self.model_id = (model_id or "").strip()
        self._model_id_explicit = bool(self.model_id)
        # Unload previously-loaded server models at connect time: None
        # follows the AUDIOCPP_UNLOAD_MODELS setting (read at connect, so
        # a Settings change this session is honored); True/False force it
        # regardless of the setting ("All (multiple generation)" runs pass
        # True so each per-model conversion starts with a clean VRAM).
        self._unload_models_override = unload_models
        # Validate before connecting so bad values fail fast without a server.
        self.language = normalize_language(
            language if language is not None else config.LANGUAGE)
        # One seed value per run, reused for every request (see
        # resolve_request_seed). Unlike the Qwen demo, audio.cpp has no
        # negative "randomize" seed, so a negative value means "send no seed
        # at all" (see _request_wav) and the server randomizes.
        self._seed = resolve_request_seed()
        # Voice selection (the --voice name). preset_mode / speaker_mode are
        # resolved in _connect: a --voice that names a built-in CustomVoice
        # speaker on a speaker-capable entry selects speaker mode; every
        # other name (and any name on a clone-capable entry) is a server-side
        # preset. The request's "voice" field (self.voice) is filled in
        # _connect per the mode.
        self.preset_mode = False
        self.speaker_mode = False
        self.voice = voice or None
        # Style/voice-design instruction sent with every request (the CLI
        # --instructions flag / the Generate form's Instructions field).
        # For task "vdes" entries it describes the voice to design; for other
        # families it is a generic style instruction when the model reads one.
        self.instructions = (instructions or "").strip()
        # Free-form per-request options (--option KEY=VALUE) forwarded in the
        # request's "options" object; models ignore keys they don't know.
        self.request_options: Dict[str, str] = dict(request_options or {})
        # Set during _connect: design_mode for "vdes" entries, instruction_voice
        # when a family without built-in speakers gets its voice from the
        # instruction alone (no voice field), and plain_mode for plain-TTS
        # runs on families that synthesize without a reference voice (also
        # no voice field). self.voice is also finalized there (the
        # speaker/preset name).
        self.design_mode = False
        self.instruction_voice = False
        self.plain_mode = False
        # Family and task of the selected model entry and the family's request
        # profile; all are resolved from GET /v1/models during _connect.
        self.family = ""
        self.task = AUDIOCPP_TASK_TTS
        self.profile = AUDIOCPP_DEFAULT_FAMILY_PROFILE
        self._connect()

    # ------------------------------------------------------------------
    # Connection
    # ------------------------------------------------------------------

    def _connected(self, mode: str) -> None:
        """Report the resolved connection (MODE: speaker/voice/... label)."""
        self._report(f"[OK] Connected to audio.cpp server at {self.api_url} "
                     f"(model '{self.model_id}', family '{self.family}', "
                     f"{mode})")

    def _connect(self) -> None:
        """Health-check the server and resolve the model, family, task, and voice.

        The entry's voice capability (audiocpp_entry_voice_capability, from
        family/task/id) plus the caller's --voice/--instructions pick the
        mode. An explicit --voice on a speaker-capable (CustomVoice) entry
        that names a built-in speaker selects speaker mode; every other
        --voice is a server-side preset, validated against the server's
        voice library. Without a --voice, design entries require
        --instructions, families that synthesize without a reference voice
        (pure-TTS, or mixed tts+clone used plainly) run in plain mode, and
        every other capability requires --voice — the run fails fast with
        a hint instead of silently synthesizing with a random default
        voice.
        """
        self._check_health()
        models = self._list_models()
        self._auto_pick_model_id(models)
        if self.voice is not None:
            # Explicit --voice: decide between speaker mode and a server-side
            # preset. A name matching a built-in CustomVoice speaker on a
            # speaker-capable primary selects speaker mode; every other name
            # (and any name when the primary entry is absent) is a preset,
            # validated against the server's voice library.
            primary = next((m for m in models if m["id"] == self.model_id),
                           None)
            if primary is not None:
                self._resolve_family(models)
                self._resolve_task(models)
                capability = audiocpp_entry_voice_capability(
                    self.family, self.task, self.model_id)
                if capability == AUDIOCPP_VOICE_SPEAKER \
                        and is_builtin_speaker(self.voice):
                    self._require_synthesis_task(models)
                    self.voice = speaker_display_name_for(self.voice)
                    self.speaker_mode = True
                    self._connected(f"speaker '{self.voice}'")
            if not self.speaker_mode:
                # Server-side preset (--voice): validate it.
                self.preset_mode = True
                self._require_model_id(models)
                self._resolve_family(models)
                self._resolve_task(models)
                self._require_synthesis_task(models)
                if self.design_mode:
                    raise RuntimeError(
                        f"--voice cannot be used with the voice design model "
                        f"'{self.model_id}': the voice is described by the "
                        "--instructions text instead (see README).")
                self._check_voice()
                self._connected(f"voice '{self.voice}'")
        else:
            # No flag: the entry's capability picks the default mode.
            self._require_model_id(models)
            self._resolve_family(models)
            self._resolve_task(models)
            self._require_synthesis_task(models)
            capability = audiocpp_entry_voice_capability(
                self.family, self.task, self.model_id)
            if self.design_mode:
                if not self.instructions:
                    raise RuntimeError(
                        f"The audio.cpp model '{self.model_id}' (family "
                        f"'{self.family}') is a voice design model: pass a "
                        "description of the voice to synthesize with, e.g. "
                        '--instructions "A warm adult female narrator with a '
                        'British accent" (see README).')
                self._connected("voice design")
                self._report(f"[INFO] Designing the voice from: {self.instructions}")
            elif capability == AUDIOCPP_VOICE_SPEAKER:
                # No --voice on a CustomVoice entry: refuse instead of
                # guessing a built-in speaker.
                raise RuntimeError(
                    f"The audio.cpp model '{self.model_id}' (family "
                    f"'{self.family}') serves built-in speakers: pass "
                    "--voice NAME with one of them (e.g. Vivian, Ryan, "
                    "Uncle Fu) to synthesize with it (see README).")
            elif self.instructions:
                # Families without built-in speakers can still get their voice
                # from the instruction alone (e.g. OmniVoice voice design).
                self.instruction_voice = True
                self._connected("instruction voice")
                self._report(f"[INFO] Designing the voice from: {self.instructions}")
            elif audiocpp_family_voice_policy(self.family) in (
                    AUDIOCPP_VOICE_OPTIONAL, AUDIOCPP_VOICE_NONE):
                # The family synthesizes without a reference voice — a
                # pure-TTS family (spec tasks without "clone") or a mixed
                # tts+clone family used without one. Plain TTS: no voice
                # field is sent at all.
                self.plain_mode = True
                self._connected("plain TTS")
            else:
                raise RuntimeError(
                    f"The audio.cpp model '{self.model_id}' (family "
                    f"'{self.family}') has no built-in speakers, so its voice "
                    "must come from the server: rerun with --voice NAME "
                    "matching a voice_preset or voice_dir entry in the server "
                    "config, or describe a voice with --instructions for "
                    "families that support it, or select the CustomVoice entry "
                    "for built-in speakers (see README).")
        if self.instructions and not self.design_mode and not self.instruction_voice:
            self._report(f"[INFO] Sending instruction with every request: {self.instructions}")
            self._report("[INFO] Its effect (style, emotion, delivery) depends on the "
                         "model family; models without instruction support ignore it.")
        unload = (config.AUDIOCPP_UNLOAD_MODELS
                  if self._unload_models_override is None
                  else self._unload_models_override)
        if unload:
            self._unload_server_models()

    def _require_synthesis_task(self, models: List[Dict[str, str]]) -> None:
        """Reject model entries that cannot synthesize narration from text.

        Two kinds of refusal: an entry hosted with a non-synthesis task
        (asr, vc, s2s, ...), and an entry whose *family* has no
        text-synthesis task at all in its model spec (e.g. PersonaPlex,
        speech-to-speech-only — its sessions reject every request with
        "supports only speech-to-speech sessions" regardless of hosting).
        """
        if self.task not in AUDIOCPP_SYNTHESIS_TASKS:
            available = ", ".join(model["id"] for model in models) or "none"
            raise RuntimeError(
                f"The audio.cpp model '{self.model_id}' has task "
                f"'{self.task}'; audiobook.py can only synthesize with TTS "
                f"model entries (tasks {', '.join(AUDIOCPP_SYNTHESIS_TASKS)}). "
                f"Pick a synthesis entry with --model (available: {available})."
            )
        if audiocpp_family_narrates(self.family) is False:
            available = ", ".join(model["id"] for model in models) or "none"
            raise RuntimeError(
                f"The audio.cpp model '{self.model_id}' (family "
                f"'{self.family}') is speech-to-speech, not TTS: it only "
                "transforms audio and cannot synthesize narration from "
                "text, so it cannot generate audiobooks. Consider "
                "deleting the model (re-run Configure Backends → "
                "audio.cpp and unselect it), or pick a TTS model entry "
                f"with --model (available: {available})."
            )

    def _unload_server_models(self) -> None:
        """Ask the server to unload every loaded model before generating.

        Lazy-loaded entries stay resident until the server exits (unless its
        max_loaded_models setting bounds residency), so switching between
        configured models across runs can exhaust device memory. Unloading
        first frees those leftovers; this run's model reloads transparently
        on its first request. Failures only warn: an older server without
        the endpoint, or a busy one, must not block a working setup.
        Controlled by config.AUDIOCPP_UNLOAD_MODELS (the TUI Settings
        "Unload models" option), or forced per run via the unload_models
        override ("All (multiple generation)" runs unload between models).
        """
        request = urllib.request.Request(
            f"{self.api_url}/v1/tasks/unload_all_models", data=b"",
            method="POST", headers={"Content-Type": "application/json"})
        try:
            with urllib.request.urlopen(request, timeout=10) as response:
                payload = json.loads(response.read().decode("utf-8"))
        except Exception as exc:
            self._report(f"[WARNING] Could not unload previously loaded models at "
                         f"{self.api_url}: {exc}")
            return
        unloaded = [entry for entry in (payload.get("unloaded") or [])
                    if isinstance(entry, str)]
        if unloaded:
            self._report(f"[OK] Unloaded {len(unloaded)} model(s) from server memory: "
                         f"{', '.join(unloaded)}")
        else:
            logger.debug("No loaded audio.cpp models to unload at %s", self.api_url)

    def _get_json(self, path: str, timeout: int = 10) -> Dict[str, Any]:
        """GET a JSON document from the server."""
        url = f"{self.api_url}{path}"
        try:
            with urllib.request.urlopen(url, timeout=timeout) as response:
                return json.loads(response.read().decode("utf-8"))
        except urllib.error.HTTPError as exc:
            detail = ""
            try:
                detail = exc.read().decode("utf-8", errors="replace")[:200]
            except Exception:
                pass
            raise RuntimeError(
                f"audio.cpp server returned HTTP {exc.code} for {path}: {detail}") from exc
        except urllib.error.URLError as exc:
            raise RuntimeError(f"audio.cpp request failed for {path}: {exc.reason}") from exc

    def _check_health(self) -> None:
        """Verify the server is reachable and reports healthy."""
        try:
            payload = self._get_json("/health")
        except Exception as exc:
            raise RuntimeError(
                f"audio.cpp server not reachable at {self.api_url}: {exc}. "
                "Start audiocpp_server first (see the 'audio.cpp backend' "
                "section of the README)."
            ) from exc
        if payload.get("status") != "ok":
            raise RuntimeError(
                f"The audio.cpp server at {self.api_url} reports status "
                f"{payload.get('status')!r} instead of 'ok'")

    def _list_models(self) -> List[Dict[str, str]]:
        """Fetch the (id, family, task) triples reported by the server."""
        try:
            payload = self._get_json("/v1/models")
        except Exception as exc:
            raise RuntimeError(
                f"The audio.cpp server at {self.api_url} did not answer "
                f"/v1/models: {exc}") from exc
        entries = payload.get("data") or []
        models: List[Dict[str, str]] = []
        for entry in entries:
            if isinstance(entry, dict) and entry.get("id"):
                models.append({
                    "id": entry["id"],
                    "family": entry.get("family") or "",
                    "task": entry.get("task") or "",
                })
        return models

    def _auto_pick_model_id(self, models: List[Dict[str, str]]) -> None:
        """Resolve an empty model id when the server hosts exactly one entry.

        Multi-model servers generated with several lazily-loaded entries
        need an explicit ``--model``, since guessing would risk
        synthesizing a whole book with the wrong family.
        """
        if self.model_id:
            return
        if len(models) == 1:
            self.model_id = models[0]["id"]
            logger.info(
                "No --model given; using the only server entry '%s'",
                self.model_id)
        else:
            logger.debug(
                "No --model given and the server hosts %d entries; "
                "an explicit --model is required",
                len(models))

    def _require_model_id(self, models: List[Dict[str, str]]) -> None:
        """Verify the model id chosen for this run exists on the server."""
        model_ids = [model["id"] for model in models]
        if self.model_id and self.model_id in model_ids:
            return
        configured = ", ".join(model_ids) or "none"
        if not self.model_id:
            raise RuntimeError(
                f"The audio.cpp server at {self.api_url} hosts {len(model_ids)} "
                f"model entries ({configured}); audiobook.py needs to know which "
                "one to use. Pass --model <id> when converting (see README)."
            )
        if self.preset_mode:
            raise RuntimeError(
                f"The audio.cpp server at {self.api_url} has no model id "
                f"'{self.model_id}' (configured: {configured}). Pass "
                "--model <id> naming one of the hosted TTS model entries "
                "(see README)."
            )
        raise RuntimeError(
            f"The audio.cpp server at {self.api_url} has no model id "
            f"'{self.model_id}' (configured: {configured}). Select the "
            "Qwen3-TTS CustomVoice entry for built-in speakers, or rerun "
            "with --voice NAME matching a voice_preset or voice_dir entry "
            "on any TTS model (see README)."
        )

    def _resolve_family(self, models: List[Dict[str, str]]) -> None:
        """Resolve the selected model's family and its request profile.

        The family comes from GET /v1/models; a missing family is an unknown
        family that falls through to the generic (clone-only) profile rather
        than guessing a specific one — audiocpp_server always reports family
        for entries its server.json describes.
        """
        entry = next(
            (model for model in models if model["id"] == self.model_id), None)
        family = (entry["family"] if entry is not None else "") or ""
        self.family = family
        self.profile = AUDIOCPP_FAMILY_PROFILES.get(
            family, AUDIOCPP_DEFAULT_FAMILY_PROFILE)
        if not family:
            logger.debug("Model '%s' reported no family; using the generic "
                         "profile", self.model_id)
        elif family not in AUDIOCPP_FAMILY_PROFILES:
            logger.info(
                "audio.cpp family '%s' has no dedicated profile; using the "
                "generic profile (voice cloning via --voice, model-detected "
                "language)", family)

    def _resolve_task(self, models: List[Dict[str, str]]) -> None:
        """Resolve the selected model's task (tts, clon, vdes, ...) and set
        design mode for voice design entries.

        The task comes from GET /v1/models and is fixed per server entry by
        its server.json config (a VoiceDesign model must be hosted with
        "task": "vdes"). Servers that predate the task field hosted plain
        TTS models, so a missing task is treated as tts.
        """
        entry = next(
            (model for model in models if model["id"] == self.model_id), None)
        task = (entry["task"] if entry is not None else "") or ""
        if not task:
            task = AUDIOCPP_TASK_TTS
            logger.debug("Model '%s' reported no task; assuming tts",
                         self.model_id)
        self.task = task
        self.design_mode = task == AUDIOCPP_TASK_VDES
        if self.family in AUDIOCPP_CLONE_ONLY_FAMILIES \
                and self.task == AUDIOCPP_TASK_TTS:
            # The session is created from the entry's hosting task, so a
            # clone-only family hosted with "tts" fails every request at
            # session-creation time — before any synthesis. Refuse here
            # with the fix instead of letting the server 500 each chunk.
            raise RuntimeError(
                f"The audio.cpp model '{self.model_id}' (family "
                f"'{self.family}') only synthesizes by cloning a reference "
                "voice, but its server entry is hosted with task 'tts', "
                "which the model rejects on every request. Re-run "
                "Configure Backends → audio.cpp to re-host it with task "
                '"clon", then restart the server.')

    def _check_voice(self) -> None:
        """Verify the requested voice is available on the server.

        A voice name that matches no server preset or voice-library wav
        would be passed through to the model as a cached voice id; on the
        Base (cloning) model that is silently ignored and plain TTS audio
        comes back, so preset names are validated up front. When the
        voices endpoint cannot be queried, validation is skipped with a
        warning rather than blocking the run.
        """
        query = urllib.parse.urlencode({"model": self.model_id})
        try:
            payload = self._get_json(f"/v1/audio/voices?{query}")
        except Exception as exc:
            logger.warning("Could not list server voices; skipping voice "
                           "validation: %s", exc)
            return
        voices = payload.get("voices") or []
        if self.voice not in voices:
            available = ", ".join(str(v) for v in voices) or "none"
            raise RuntimeError(
                f"Voice '{self.voice}' is not available on the audio.cpp server "
                f"(available: {available}). Configure it as a voice_preset or "
                "voice_dir entry in the server config, or pass a listed name "
                "with --voice (see README)."
            )

    # ------------------------------------------------------------------
    # HTTP requests
    # ------------------------------------------------------------------

    def _request_wav(self, text: str) -> bytes:
        """POST one sub-chunk and return the raw WAV bytes."""
        url = f"{self.api_url}/v1/audio/speech"
        input_text = text
        if self.profile.script_prefix:
            # Script-parsed families (VibeVoice) drop unprefixed lines:
            # flatten the sub-chunk into one prefixed script line.
            input_text = audiocpp_script_input(self.profile.script_prefix,
                                               text)
        payload: Dict[str, Any] = {
            "model": self.model_id,
            "input": input_text,
        }
        # Design models take no voice field (the voice comes from the
        # instruction); instruction-voice runs on families without built-in
        # speakers omit it too, since no speaker or preset was requested;
        # plain-TTS runs (no reference voice needed) omit it likewise.
        if not self.design_mode and not self.instruction_voice \
                and not self.plain_mode:
            payload["voice"] = self.voice
        if self.profile.language_style == AUDIOCPP_LANG_DISPLAY:
            payload["language"] = self.language
        elif self.profile.language_style == AUDIOCPP_LANG_ISO:
            iso_code = LANGUAGE_ISO_CODES.get(self.language)
            if iso_code:
                payload["language"] = iso_code
            else:
                # "Auto": no code to send, so let the server pick its default.
                logger.debug("%s: no language code for %r; omitted from request",
                             self.family, self.language)
        if self._seed >= 0:
            # audio.cpp has no negative "randomize" seed; a negative seed
            # means "let the server randomize", so the field is omitted.
            payload["seed"] = self._seed
        if self.instructions:
            # Explicit voice-design or style instruction (required for task
            # "vdes" entries; a Ctrl/style control on families that read it).
            payload["instructions"] = self.instructions
        if self.request_options:
            # Generic per-model controls (--option KEY=VALUE): forwarded
            # verbatim; the model ignores keys it does not know.
            payload["options"] = dict(self.request_options)
        request = urllib.request.Request(
            url, data=json.dumps(payload).encode("utf-8"),
            headers={"Content-Type": "application/json"}, method="POST")
        timeout = config.API_TIMEOUT
        try:
            with urllib.request.urlopen(request, timeout=timeout) as response:
                wav = response.read()
        except urllib.error.HTTPError as exc:
            detail = ""
            try:
                detail = exc.read().decode("utf-8", errors="replace")[:200]
            except Exception:
                pass
            raise audiocpp_request_error(exc.code, detail,
                                         voice=self.voice) from exc
        except urllib.error.URLError as exc:
            raise RuntimeError(f"audio.cpp request failed: {exc.reason}") from exc
        if len(wav) < 12 or wav[:4] != b"RIFF" or wav[8:12] != b"WAVE":
            raise RuntimeError("audio.cpp server returned audio that is not a WAV file")
        return wav

    # ------------------------------------------------------------------
    # Chunk generation
    # ------------------------------------------------------------------

    def generate_chunk(self, text: str, chunk_num: int) -> Optional[str]:
        """Generate one audio chunk; returns its path in the chunks folder.

        The text is split into sub-requests of at most ``config.CHUNK_SIZE``
        words each; each sub-request returns a complete WAV file and the
        parts are concatenated into one chunk file.
        """
        try:
            sub_texts = split_into_chunks(text, max_words=config.CHUNK_SIZE)
            if not sub_texts:
                raise RuntimeError("No text to synthesize")

            output_path: Optional[Path] = None
            with tempfile.TemporaryDirectory(prefix="tts_parts_") as parts_dir, \
                    self._chunk_heartbeat(chunk_num):
                part_paths = []
                for sub_num, sub_text in enumerate(sub_texts, 1):
                    wav = self._request_wav(sub_text)
                    destination = Path(parts_dir) / f"part_{sub_num:02d}.wav"
                    destination.write_bytes(wav)
                    part_paths.append(destination)
                if len(part_paths) == 1:
                    output_path = self._chunk_path(chunk_num, ".wav")
                    shutil.copy2(part_paths[0], output_path)
                else:
                    output_path = self._chunk_path(chunk_num, ".wav")
                    concat_audio_files(part_paths, output_path)

            logger.debug("Chunk %d generated successfully (%d sub-request(s))",
                         chunk_num, len(sub_texts))
            return str(output_path)

        except ConversionCancelled:
            raise
        except NonRetryableTTSError:
            # Propagate past the generic handler so the retry loop skips
            # its remaining attempts for deterministic server errors.
            raise
        except Exception as exc:
            logger.error("audio.cpp chunk processing failed for chunk %d: %s",
                         chunk_num, exc)
            return None