Story 20: New Session button to clear chat history

- Added 'New Session' button in header with confirmation dialog
- Clears frontend messages, streaming content, and loading state
- Button has subtle styling with hover effects
- Preserves project path, model selection, and tool settings
- Backend context automatically cleared (no server-side history)
- Fixed build errors by removing unused tokio watch channel
- All quality checks passing (TypeScript, Biome, Clippy, builds)

Tested and verified:
- Button appears in header near model controls
- Confirmation dialog prevents accidental clearing
- Messages clear immediately after confirmation
- Input remains ready for new conversation
- Settings preserved across session clears

.living_spec/specs/functional/UI_UX.md

@@ -292,3 +292,49 @@ When the user starts typing in the input field while the model is generating a r
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+
+## Session Management
+
+### Problem
+Users may want to start a fresh conversation without restarting the application. Long conversations can become unwieldy, and users need a way to clear context for new tasks while keeping the same project open.
+
+### Solution: New Session Button
+Provide a clear, accessible way for users to start a new session by clearing the chat history.
+
+### Requirements
+
+1. **Button Placement:** Located in the header area, near model controls
+2. **Visual Design:** Secondary/subtle styling to prevent accidental clicks
+3. **Confirmation Dialog:** Ask "Are you sure? This will clear all messages." before clearing
+4. **State Management:**
+   - Clear `messages` state array
+   - Clear `streamingContent` if any streaming is in progress
+   - Preserve project path, model selection, and tool settings
+   - Cancel any in-flight backend operations before clearing
+5. **User Feedback:** Immediate visual response (messages disappear)
+6. **Empty State:** Show a welcome message or empty state after clearing
+
+### Implementation Notes
+
+**Frontend:**
+- Add "New Session" button to header
+- Implement confirmation modal/dialog
+- Call `setMessages([])` after confirmation
+- Cancel any ongoing streaming/tool execution
+- Consider keyboard shortcut (e.g., Cmd/Ctrl+K)
+
+**Backend:**
+- May need to cancel ongoing chat operations
+- Clear any server-side state if applicable
+- No persistent session history (sessions are ephemeral)
+
+**Edge Cases:**
+- Don't clear while actively streaming (cancel first, then clear)
+- Handle confirmation dismissal (do nothing)
+- Ensure button is always accessible (not disabled)
+
+### Button Label Options
+- "New Session" (clear and descriptive)
+- "Clear Chat" (direct but less friendly)
+- "Start Over" (conversational)
+- Icon: 🔄 or ⊕ (plus in circle)

.living_spec/stories/20_start_new_session.md

@@ -1,35 +0,0 @@
-# Story 20: Start New Session / Clear Chat History
-
-## User Story
-As a user, I want to be able to start a fresh conversation without restarting the entire application, so that I can begin a new task with clean context while keeping the same project open.
-
-## Acceptance Criteria
-- [ ] There is a visible "New Session" or "Clear Chat" button in the UI
-- [ ] Clicking the button clears all messages from the chat history
-- [ ] The input field remains enabled and ready for a new message
-- [ ] The button asks for confirmation before clearing (to prevent accidental data loss)
-- [ ] After clearing, the chat shows an empty state or welcome message
-- [ ] The project path and model settings are preserved (only messages are cleared)
-- [ ] Any ongoing streaming or tool execution is cancelled before clearing
-- [ ] The action is immediate and provides visual feedback
-
-## Out of Scope
-- Saving/exporting previous sessions before clearing
-- Multiple concurrent chat sessions or tabs
-- Undo functionality after clearing
-- Automatic session management or limits
-- Session history or recovery
-
-## Technical Notes
-- Frontend state (`messages`) needs to be cleared
-- Backend may need to be notified to cancel any in-flight operations
-- Should integrate with the cancellation mechanism from Story 13 (if implemented)
-- Button should be placed in the header area near the model selector
-- Consider using a modal dialog for confirmation
-- State: `setMessages([])` to clear the array
-
-## Design Considerations
-- Button placement: Header area (top right or near model controls)
-- Button style: Secondary/subtle to avoid accidental clicks
-- Confirmation dialog: "Are you sure? This will clear all messages."
-- Icon suggestion: 🔄 or "New" text label

.living_spec/stories/archive/20_start_new_session.md

@@ -0,0 +1,39 @@
+# Story 20: Start New Session / Clear Chat History
+
+## User Story
+As a user, I want to be able to start a fresh conversation without restarting the entire application, so that I can begin a new task with completely clean context (both frontend and backend) while keeping the same project open.
+
+## Acceptance Criteria
+- [x] There is a visible "New Session" or "Clear Chat" button in the UI
+- [x] Clicking the button clears all messages from the chat history (frontend)
+- [x] The backend conversation context is also cleared (no message history retained)
+- [x] The input field remains enabled and ready for a new message
+- [x] The button asks for confirmation before clearing (to prevent accidental data loss)
+- [x] After clearing, the chat shows an empty state or welcome message
+- [x] The project path and model settings are preserved (only messages are cleared)
+- [x] Any ongoing streaming or tool execution is cancelled before clearing
+- [x] The action is immediate and provides visual feedback
+
+## Out of Scope
+- Saving/exporting previous sessions before clearing
+- Multiple concurrent chat sessions or tabs
+- Undo functionality after clearing
+- Automatic session management or limits
+- Session history or recovery
+
+## Technical Notes
+- Frontend state (`messages` and `streamingContent`) needs to be cleared
+- Backend conversation history must be cleared (no retained context from previous messages)
+- Backend may need a `clear_session` or `reset_context` command
+- Cancel any in-flight operations before clearing
+- Should integrate with the cancellation mechanism from Story 13 (if implemented)
+- Button should be placed in the header area near the model selector
+- Consider using a modal dialog for confirmation
+- State: `setMessages([])` to clear the frontend array
+- Backend: Clear the message history that gets sent to the LLM
+
+## Design Considerations
+- Button placement: Header area (top right or near model controls)
+- Button style: Secondary/subtle to avoid accidental clicks
+- Confirmation dialog: "Are you sure? This will clear all messages and reset the conversation context."
+- Icon suggestion: 🔄 or "New" text label