fix: SPA middleware instead of catch-all, preserves WS

backend/main.py

@@ -1003,17 +1003,36 @@ async def serve_index():
     return {"message": "Claude Persistent Agent API v3.0", "docs": "/docs"}
 
 
-@app.get("/{full_path:path}")
-async def serve_spa(full_path: str):
-    """Serve React SPA for all non-API routes. API and WS are handled above."""
-    if full_path.startswith("api"):
-        raise HTTPException(404)
-    # Try serving the file directly (e.g. vite.svg, favicon)
-    file_path = STATIC_DIR / full_path
-    if file_path.is_file():
-        return FileResponse(str(file_path))
-    # Fall back to index.html for SPA routing
+@app.get("/vite.svg")
+@app.get("/favicon.ico")
+async def serve_static_root_files():
+    """Serve known static root files."""
+    from starlette.requests import Request
+    return FileResponse(str(STATIC_DIR / "vite.svg"))
+
+
+# SPA fallback via middleware — this avoids the catch-all route problem
+# that breaks WebSocket routing in some Starlette versions
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.requests import Request as StarletteRequest
+from starlette.responses import Response
+
+
+class SPAFallbackMiddleware(BaseHTTPMiddleware):
+    async def dispatch(self, request: StarletteRequest, call_next):
+        response = await call_next(request)
+        # If a non-API GET request returned 404, serve index.html for SPA
+        if (response.status_code == 404
+                and request.method == "GET"
+                and not request.url.path.startswith("/api")
+                and not request.url.path.startswith("/docs")
+                and not request.url.path.startswith("/openapi")
+                and not request.url.path.startswith("/assets")
+                and "websocket" not in request.headers.get("upgrade", "").lower()):
             index = STATIC_DIR / "index.html"
             if index.exists():
                 return FileResponse(str(index))
-    raise HTTPException(404)
+        return response
+
+
+app.add_middleware(SPAFallbackMiddleware)