voice-out-elevenlabs: ElevenLabs TTS voice-out channel

[webdevtodayjason]

Summary

• New src/channels/voice-out.ts exposing createVoiceOutChannel({ bus, getKey, ... }).
• Subscribes to bus (cli by default); on kind: "completion" POSTs {text, model_id} to https://api.elevenlabs.io/v1/text-to-speech/{voiceId}/stream?output_format=pcm_22050 with xi-api-key, then streams PCM response chunks into the aplay child stdin.
• kind: "error" triggers the same pipeline with a short apology string.
• fetchImpl and spawn are injectable; default spawn uses node:child_process and invokes aplay -q -f S16_LE -r 22050 -c 1.
• stop() unsubscribes and ends the aplay stream. Strict TS, no any, no globals mutated.

Validation

• pnpm check → exit 0
• pnpm test tests/channels/voice-out.test.ts → 3/3 passed

Test plan

• Fake bus + fake fetch (ReadableStream of PCM) + fake spawn (PassThrough): asserts URL, xi-api-key, body, aplay args, and that PCM bytes flow to the injected stream.
• Error message path invokes TTS with an apology body.
• stop() unsubscribes from the bus and calls .end() on the aplay stream.

Contract: ops/contracts/engineer-auth.contract.md
Slice: voice-out-elevenlabs

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