fix(mcp): refuse subscriptions/listen streams — MCP serving is stateless (EVE-95) (#548)

src/server/mcp/server.ts

@@ -143,6 +143,11 @@ export function createOpenSeoMcpServer(authProps: McpProps) {
       ],
     },
     {
+      // The tool list is fixed per request and no list_changed notification
+      // is ever published, so don't advertise the capability — modern clients
+      // use it to decide whether to open a subscriptions/listen stream.
+      // Without the pre-declaration, registerTool defaults it to true.
+      capabilities: { tools: { listChanged: false } },
       instructions:
         "OpenSEO research tools use credits. Proceed with normal focused research, but ask the user for confirmation before planned batches over 2,000 credits.",
     },

src/server/mcp/transport.ts

@@ -128,6 +128,12 @@ function createRequestHandler(
     route: MCP_ROUTE,
     allowedOriginHostnames,
     legacy: "reject",
+    // MCP serving is strictly stateless: no notification is ever published,
+    // so refuse subscriptions/listen outright (in-band -32603 before the
+    // ack). The SSE streams it would otherwise hold open pin isolates for
+    // hours and turn every isolate death into a burst of exceededMemory
+    // request outcomes (EVE-95).
+    maxSubscriptions: 0,
   });
 
   return async (request: Request, env: unknown, ctx: ExecutionContext) => {