From 3e1be88c3bf20bcaf8cb007d190c708f69057fee Mon Sep 17 00:00:00 2001
From: Greg King <greg@dotsetlabs.com>
Date: Mon, 26 Jan 2026 09:10:58 -0500
Subject: [PATCH] fix(everything): allow re-registration of session resources

When a tool like `gzip-file-as-resource` is called multiple times with the
same output name (especially the default `README.md.gz`), the server would
throw "Resource already registered" because the SDK doesn't allow
registering duplicate URIs.

This fix:
- Tracks registered resources by URI in a module-level Map
- Before registering a new resource, checks if the URI already exists
- If it does, removes the old resource using the SDK's `remove()` method
- Then registers the new resource with fresh content

This allows tools to be called repeatedly with the same parameters without
errors, which is important for LLM agents that may retry tool calls.

Found using Bellwether (https://bellwether.sh), an MCP server validation tool.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 src/everything/resources/session.ts | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/everything/resources/session.ts b/src/everything/resources/session.ts
index f4e16d3b78..10e0db33c1 100644
--- a/src/everything/resources/session.ts
+++ b/src/everything/resources/session.ts
@@ -1,6 +1,13 @@
-import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { McpServer, RegisteredResource } from "@modelcontextprotocol/sdk/server/mcp.js";
 import { Resource, ResourceLink } from "@modelcontextprotocol/sdk/types.js";
 
+/**
+ * Tracks registered session resources by URI to allow updating/removing on re-registration.
+ * This prevents "Resource already registered" errors when a tool creates a resource
+ * with the same URI multiple times during a session.
+ */
+const registeredResources = new Map<string, RegisteredResource>();
+
 /**
  * Generates a session-scoped resource URI string based on the provided resource name.
  *
@@ -47,17 +54,27 @@ export const registerSessionResource = (
           blob: payload,
         };
 
+  // Check if a resource with this URI is already registered and remove it
+  const existingResource = registeredResources.get(uri);
+  if (existingResource) {
+    existingResource.remove();
+    registeredResources.delete(uri);
+  }
+
   // Register file resource
-  server.registerResource(
+  const registeredResource = server.registerResource(
     name,
     uri,
     { mimeType, description, title, annotations, icons, _meta },
-    async (uri) => {
+    async () => {
       return {
         contents: [resourceContent],
       };
     }
   );
 
+  // Track the registered resource for potential future removal
+  registeredResources.set(uri, registeredResource);
+
   return { type: "resource_link", ...resource };
 };