docs(design): voice integration with Yapper

[dimakis]

Summary

• Design doc for Mitzo ↔ Yapper voice integration
• Client-direct architecture: frontend talks to Yapper for STT/TTS, server stays text-only
• Push-to-talk input, optional TTS output, graceful degradation when Yapper is down
• No v2 protocol changes — voice is a preprocessing/postprocessing layer

Implementation phases

1. Batch STT — mic button, record, POST to Yapper, insert transcript
2. TTS playback — toggle to hear responses via Yapper synthesize
3. Streaming STT — live partial transcripts via WebSocket

Test plan

• Review design doc for completeness and feasibility
• Confirm architecture aligns with existing Mitzo patterns

🤖 Generated with Claude Code

[dimakis]

Design review — looks solid. A few gaps to address before or during implementation:

Browser permissions

• navigator.mediaDevices.getUserMedia requires explicit user permission. Need a permission flow: prompt on first mic tap, handle denial gracefully (show "mic blocked" state, not just hidden button).

Safari MediaRecorder compatibility

• Safari's MediaRecorder support for video/webm / audio/webm;codecs=opus is inconsistent. iOS Safari may require audio/mp4 fallback. The audio.ts module should negotiate mimeType at runtime (MediaRecorder.isTypeSupported()), and Yapper's format negotiation frame needs to handle whatever format the browser actually produces.

Yapper model readiness (resolved)

• Open question #5 is addressed by dimakis/yapper#7 — /health now returns {"status": "ready"|"loading", "models": {"stt": bool, "tts": bool}} with 503 while loading. Mitzo can use this to show "loading models..." instead of hiding the mic.

CORS dependency

• Client-direct architecture requires Yapper to have permissive CORS (dimakis/yapper#5 adds allow_origins=["*"]). Worth noting as a hard dependency in the doc.

Mixed content (future)

• If Mitzo is ever served over HTTPS, MediaRecorder requires a secure context and HTTP calls to Yapper would be blocked as mixed content. Not a blocker now (LAN-only), but worth a "Future Considerations" note.

Minor gaps

• MAX_RECORDING_DURATION_MS mentioned as a constant but no value or auto-stop behavior defined.
• Error UX for Yapper 500s or empty/too-short recordings not specified.
• Doc says useLongPress "already exists" — verify before assuming reuse.