- Add provider adapter layer (server/providers/) with registry pattern
- Claude, Cursor, Codex, Gemini adapters normalize native formats to NormalizedMessage
- Shared types.js defines ProviderAdapter interface and message kinds
- Registry enables polymorphic provider lookup
- Add unified REST endpoint: GET /api/sessions/:id/messages?provider=...
- Replaces four provider-specific message endpoints with one
- Delegates to provider adapters via registry
- Add frontend session-keyed store (useSessionStore)
- Per-session Map with serverMessages/realtimeMessages/merged
- Dedup by ID, stale threshold for re-fetch, background session accumulation
- No localStorage for messages — backend JSONL is source of truth
- Add normalizedToChatMessages converter (useChatMessages)
- Converts NormalizedMessage[] to existing ChatMessage[] UI format
- Wire unified store into ChatInterface, useChatSessionState, useChatRealtimeHandlers
- Session switch uses store cache for instant render
- Background WebSocket messages routed to correct session slot
