feat: rebuild Lilac into Chat/Translate/Transcribe mode runtimes

[DexterStorey]

Summary

• rebuild Lilac into explicit chat, translate, and transcribe modes with mode-specific UI surfaces
• replace legacy realtime provider/session path with a mode-aware runtime and raw OpenAI API clients
• add strict Zod schemas for server actions and realtime event parsing
• implement Chat over Realtime WebRTC (client_secrets + realtime/calls)
• implement Translate/Transcribe over Realtime transcription WebSocket (transcription_sessions)
• add deterministic translation action via Responses API with structured JSON output
• add context compaction/bounded context flow for long translation sessions
• enforce mode switch semantics: stop current session, clear in-memory state, start next session

Key Refactor

• split monolithic ToggleRealtime into:
  • ChatMode.tsx
  • TranslateMode.tsx
  • TranscribeMode.tsx
  • ModeShell.tsx
• replace legacy provider with:
  • sessionTypes.ts
  • chatRealtimeClient.ts
  • transcriptionSocketClient.ts
  • modeRuntimeStore.tsx
• replace legacy server action path with:
  • createRealtimeClientSecretAction
  • createRealtimeTranscriptionSessionAction
  • translateUtteranceAction
  • compactTranslationContextAction

Validation

• bun x biome check . passes
• bun run build passes

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Project	Deployment	Actions	Updated (UTC)
lilac	Building	Preview, Comment	Mar 2, 2026 9:48pm