fix: replace BaseHTTPMiddleware with pure ASGI middleware for WebSocket compat

backend/main.py

@@ -1011,28 +1011,81 @@ async def serve_static_root_files():
     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
+# SPA fallback via pure ASGI middleware — BaseHTTPMiddleware breaks WebSocket
+# routing in Starlette 0.27.x, so we use a raw ASGI wrapper instead.
 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()):
+class SPAFallbackMiddleware:
+    """Pure ASGI middleware that serves index.html for unknown GET routes.
+    Unlike BaseHTTPMiddleware, this correctly passes WebSocket connections
+    through without wrapping them."""
+
+    def __init__(self, app):
+        self.app = app
+
+    async def __call__(self, scope, receive, send):
+        # Pass WebSocket and non-HTTP connections straight through
+        if scope["type"] != "http":
+            await self.app(scope, receive, send)
+            return
+
+        path = scope.get("path", "")
+        method = scope.get("method", "GET")
+
+        # Only intercept GET requests for non-API, non-asset paths
+        skip_prefixes = ("/api", "/docs", "/openapi", "/assets")
+        if method != "GET" or any(path.startswith(p) for p in skip_prefixes):
+            await self.app(scope, receive, send)
+            return
+
+        # Capture the response status to decide if we should serve index.html
+        response_started = False
+        initial_status = None
+
+        async def send_wrapper(message):
+            nonlocal response_started, initial_status
+            if message["type"] == "http.response.start":
+                initial_status = message.get("status", 200)
+                if initial_status != 404:
+                    response_started = True
+                    await send(message)
+                # If 404, we hold off — we'll serve index.html instead
+            elif message["type"] == "http.response.body":
+                if response_started:
+                    await send(message)
+                # If not started (was 404), we drop the body
+
+        await self.app(scope, receive, send_wrapper)
+
+        # If the app returned 404, serve index.html for SPA routing
+        if not response_started and initial_status == 404:
             index = STATIC_DIR / "index.html"
             if index.exists():
-                return FileResponse(str(index))
-        return response
+                body = index.read_bytes()
+                await send({
+                    "type": "http.response.start",
+                    "status": 200,
+                    "headers": [
+                        [b"content-type", b"text/html; charset=utf-8"],
+                        [b"content-length", str(len(body)).encode()],
+                    ],
+                })
+                await send({
+                    "type": "http.response.body",
+                    "body": body,
+                })
+            else:
+                # No index.html, pass through the 404
+                await send({
+                    "type": "http.response.start",
+                    "status": 404,
+                    "headers": [[b"content-type", b"text/plain"]],
+                })
+                await send({
+                    "type": "http.response.body",
+                    "body": b"Not Found",
+                })
 
 
 app.add_middleware(SPAFallbackMiddleware)