feat(FN-2449): merge fusion/fn-2449

docs/architecture.md

@@ -401,6 +401,11 @@ Key server capabilities:
   - Project-scoped: resolves project context from query param or engine manager
 - **Chat streaming**: `/api/chat/sessions/:id/messages` (`routes.ts` + `chat.ts`)
   - Streams assistant responses as SSE events for chat sessions
+- **Chat session queries**: `/api/chat/sessions` (`routes.ts`)
+  - Existing list behavior is unchanged (`status=active|archived|all` returns an array)
+  - Quick Chat resume uses targeted lookup params: `agentId`, optional `modelProvider` + `modelId`, plus `resume=1`
+  - Validation requires `modelProvider` and `modelId` together; partial model pairs return `400`
+  - Targeted lookup returns only the newest matching active session (or `null`) to avoid scanning every active session client-side
 - **Task log stream**: `/api/tasks/:id/logs/stream` (`server.ts`)
   - SSE endpoint for live task log streaming with project scope resolution
 - **Dev-server stream**: `/api/dev-server/logs/stream` (`dev-server-routes.ts`)

docs/dashboard-guide.md

@@ -44,6 +44,9 @@ Quick Chat is an optional floating panel for fast, project-scoped assistant conv
 - Controlled by the project setting `showQuickChatFAB`
 - Supports agent mentions (`@agent`) and file mentions
 - Uses the same model/provider infrastructure as full Chat view
+- `switchSession()` resumes the existing thread for the selected target (agent-only or agent+model)
+- `startFreshSession()` is the explicit new-thread action and always creates a new persisted session
+- Resume lookups use a targeted session query instead of loading the full active session list first
 
 ## Mailbox View