From 824e914eb124ca66d8c131ef6b8fc447debe5c60 Mon Sep 17 00:00:00 2001
From: Ben Senescu <44480372+bensenescu@users.noreply.github.com>
Date: Wed, 26 Aug 2026 11:48:20 -0400
Subject: [PATCH] =?UTF-8?q?fix(mcp):=20refuse=20subscriptions/listen=20str?=
 =?UTF-8?q?eams=20=E2=80=94=20MCP=20serving=20is=20stateless=20(EVE-95)=20?=
 =?UTF-8?q?(#548)?=
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---
 src/server/mcp/server.ts    | 5 +++++
 src/server/mcp/transport.ts | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/src/server/mcp/server.ts b/src/server/mcp/server.ts
index bc5f858..806d1d5 100644
--- a/src/server/mcp/server.ts
+++ b/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.",
     },
diff --git a/src/server/mcp/transport.ts b/src/server/mcp/transport.ts
index de1cd02..42faef3 100644
--- a/src/server/mcp/transport.ts
+++ b/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) => {