docs: Comprehensive documentation update for Dashboard V3 and Canvas

## Documentation Updates
- DASHBOARD.md: Updated to V3.0 with Canvas V3 features, file browser, introspection
- DASHBOARD_IMPLEMENTATION_STATUS.md: Marked Canvas V3 features as COMPLETE
- CANVAS.md: New comprehensive guide for Canvas Builder V3 with all features
- CLAUDE.md: Added dashboard quick reference and Canvas V3 features

## Canvas V3 Features Documented
- File Browser: Browse studies directory for model files
- Model Introspection: Auto-discover expressions, solver type, dependencies
- One-Click Add: Add expressions as design variables instantly
- Claude Bug Fixes: WebSocket reconnection, SQL errors resolved
- Health Check: /api/health endpoint for monitoring

## Backend Services
- NX introspection service with expression discovery
- File browser API with type filtering
- Claude session management improvements
- Context builder enhancements

## Frontend Components
- FileBrowser: Modal for file selection with search
- IntrospectionPanel: View discovered model information
- ExpressionSelector: Dropdown for design variable configuration
- Improved chat hooks with reconnection logic

## Plan Documents
- Added RALPH_LOOP_CANVAS_V2/V3 implementation records
- Added ATOMIZER_DASHBOARD_V2_MASTER_PLAN
- Added investigation and sync documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

atomizer-dashboard/backend/api/routes/claude.py

@@ -93,7 +93,10 @@ async def create_session(request: CreateSessionRequest):
             "is_alive": session.is_alive(),
         }
     except Exception as e:
-        raise HTTPException(status_code=500, detail=str(e))
+        import traceback
+        error_msg = f"{type(e).__name__}: {str(e) or 'No message'}"
+        traceback.print_exc()
+        raise HTTPException(status_code=500, detail=error_msg)
 
 
 @router.get("/sessions/{session_id}")
@@ -146,8 +149,9 @@ async def session_websocket(websocket: WebSocket, session_id: str):
     WebSocket for real-time chat with a session.
 
     Message formats (client -> server):
-        {"type": "message", "content": "user message"}
+        {"type": "message", "content": "user message", "canvas_state": {...}}
         {"type": "set_study", "study_id": "study_name"}
+        {"type": "set_canvas", "canvas_state": {...}}
         {"type": "ping"}
 
     Message formats (server -> client):
@@ -158,6 +162,7 @@ async def session_websocket(websocket: WebSocket, session_id: str):
         {"type": "error", "message": "..."}
         {"type": "pong"}
         {"type": "context_updated", "study_id": "..."}
+        {"type": "canvas_updated", "canvas_state": {...}}
     """
     await websocket.accept()
 
@@ -169,6 +174,9 @@ async def session_websocket(websocket: WebSocket, session_id: str):
         await websocket.close()
         return
 
+    # Track current canvas state for this connection
+    current_canvas_state: Dict[str, Any] = {}
+
     try:
         while True:
             data = await websocket.receive_json()
@@ -178,7 +186,14 @@ async def session_websocket(websocket: WebSocket, session_id: str):
                 if not content:
                     continue
 
-                async for chunk in manager.send_message(session_id, content):
+                # Get canvas state from message or use stored state
+                canvas_state = data.get("canvas_state") or current_canvas_state
+
+                async for chunk in manager.send_message(
+                    session_id,
+                    content,
+                    canvas_state=canvas_state if canvas_state else None,
+                ):
                     await websocket.send_json(chunk)
 
             elif data.get("type") == "set_study":
@@ -190,6 +205,14 @@ async def session_websocket(websocket: WebSocket, session_id: str):
                         "study_id": study_id,
                     })
 
+            elif data.get("type") == "set_canvas":
+                # Update canvas state for this connection
+                current_canvas_state = data.get("canvas_state", {})
+                await websocket.send_json({
+                    "type": "canvas_updated",
+                    "canvas_state": current_canvas_state,
+                })
+
             elif data.get("type") == "ping":
                 await websocket.send_json({"type": "pong"})