The built-in Piper provider (tts.provider: piper, Python piper-tts
package) already constructs piper.SynthesisConfig for the advanced
tuning knobs, but did not forward speaker_id from the user config.
This wires tts.piper.speaker_id through to SynthesisConfig.speaker_id
so multi-speaker ONNX models (e.g. libritts_r) can be addressed via
config without dropping to the command-provider path.
Changes:
- Add speaker_id to the has_advanced tuple so setting it triggers
SynthesisConfig construction (same gating as the other knobs).
- Pass speaker_id=speaker_id to SynthesisConfig. Defaults to 0
(Piper's own default; single-speaker models ignore the field).
- Tolerant parse: bad input (non-int strings, lists, dicts) is
dropped to 0 instead of raising. Booleans are rejected outright
(True/False would silently coerce to 1/0 and hide a config
mistake). Mirrors the same shape as the command-provider's
_resolve_command_tts_optional_number helper.
speaker_id is applied per-call via syn_config.speaker_id, so the
PiperVoice cache key is intentionally left as just (model, cuda) --
the same loaded model serves all speakers. Tests cover the
config knob, the tolerant parse, and the no-reload invariant.
sentence_silence is intentionally not added here: the Python
piper-tts SynthesisConfig does not expose that field (CLI-only).
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