feat(fishaudio): use websocket API for faster inference

[davidzhao]

reducing TTFB from ~400ms to ~230ms

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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[toubatbrian]

This is an automated Claude Code Routine created by @toubatbrian. Right now it is in experimentation stage. The automation will start porting this PR into agents-js automatically.

Note: this PR contains a mix of plugin-specific (fishaudio), Python-specific (replacing the fish-audio-sdk dependency), and core runtime changes. Since agents-js does not currently have a fishaudio plugin and the dependency swap is Python-specific, only the core runtime improvements will be ported:

• tts/tts.py: don't tear the audio decoder down on a mid-stream FlushSegment (preserves stateful codec parser state for WAV/OGG/MP3).
• utils/codecs/decoder.py: gracefully handle EOF before any audio could be decoded.

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[toubatbrian]

Update from the routine: after inspecting agents-js, none of the changes in this PR have a direct port path, so no JS PR will be opened.

• fishaudio plugin rewrite (HTTP+msgpack websocket) — agents-js does not have a fishaudio plugin, so there is nothing to update.
• fish-audio-sdk → msgpack dependency swap — Python-specific, skipped per the routine's rules.
• tts/tts.py mid-stream FlushSegment decoder fix and utils/codecs/decoder.py EOFError handling — these patch the Python AudioEmitter._decode_task path which wraps a stateful FFmpeg-based streaming decoder. agents-js has no equivalent: every TTS plugin (cartesia, elevenlabs, deepgram, baseten, inworld, etc.) emits raw PCM directly via AudioByteStream, and FFmpeg is only used in agents/src/audio.ts for one-shot file playback and in recorder_io.ts for output encoding — neither has a flush()-driven decoder-teardown path or the EOF-before-any-output failure mode that the Python fixes target.

cc @toubatbrian

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Generated by Claude Code