feat(voice): trigger /canvas/speak on outbound agent chat when human is in room

[itskai-dev]

Summary

Outbound voice loop on canvas — closes the gap where agent chat replies are visually shared (via PR #2839 reply card) but acoustically per-tab (browser-driven /api/tts only plays in the asker's tab).

chatManager.sendMessage now calls triggerVoiceOnChat(message) after eventBus.emitMessagePosted. When all gates pass, it fires-and-forgets a POST to local /canvas/speak — reusing the existing voice_output SSE → voice.output Supabase broadcast path that PR #2840 already wired up to fan out audio to all canvas tabs (asker + peers + big screen).

Lane locked by kai (msg-1777815083752): smallest honest seam, gate on human presence, reuse existing path, no new endpoint/event, browser useVoice stays untouched as fallback this PR.

task: task-1777140469973-770cy4yma

Gates (all required to fire)

• channel === 'general'
• from is not 'system' / 'human' / 'user'
• content passes the speakability filter (no @-only, no commit hashes, no PR/CI status, no code-heavy, no terminal output, ≤350 chars, ≥8 chars after cleaning)
• listRoomParticipants().length > 0 — at least one human is present in the room (reuses room-presence-store from feat(chat-context): inject ROOM STATUS line when a human is in the room #1316)
• module-level dedup + 8s global cooldown (mirrors useVoice)

Speakability filter is ported verbatim from apps/web/src/app/presence/use-voice.ts:378-405 so both rails apply the same "no police scanner" bar.

Bar held (per kai)

• ✅ no new endpoint — reuses /canvas/speak
• ✅ no new event type — reuses voice_output SSE
• ✅ no new channel — reuses room:${hostId} Supabase broadcast
• ✅ no provider rewrite — Kokoro stays primary
• ✅ no push-bridge widening — voice_output SSE only reaches canvas subscribers
• ✅ no AGENTS.md changes
• ✅ browser useVoice untouched in this PR — kept as fallback, no dedupe, no delete

Files

• src/voice-on-chat.ts (NEW, ~160 LOC) — filter + gate + HTTP self-call trigger
• src/chat.ts (+5 LOC) — single hook after eventBus.emitMessagePosted
• tests/voice-on-chat.test.ts (NEW, ~120 LOC) — 18 unit tests for filter + gate

Test plan

• npx tsc --noEmit — clean
• npx vitest run tests/voice-on-chat.test.ts — 18/18 passing
• npx vitest run tests/chat-context-room-active.test.ts tests/chat-dedup.test.ts tests/chat-monotonic-timestamps.test.ts — 28/28 passing (no regressions on chat-adjacent suites)
• Canonical staging proof on e4e35463-02d7-420d-a00d-65e765ade5a2 — agent posts to #general → human in room hears voice on canvas tab + big-screen tab
• Empty-room negative — agent posts with no humans → no /canvas/speak call (silent gate)
• DM negative — agent posts to DM/non-general channel → no fire
• System negative — system message in #general → no fire

Will not auto-merge. Awaiting team ack + canonical-host proof.

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