fix(everything): scope session resources to their server

src/everything/__tests__/resources.test.ts

@@ -221,6 +221,50 @@ describe('Session Resources', () => {
       );
     });
 
+    it('should not evict a resource with the same URI from another server', () => {
+      const firstRegistration = { remove: vi.fn() };
+      const secondRegistration = { remove: vi.fn() };
+      const firstServer = {
+        registerResource: vi.fn(() => firstRegistration),
+      } as unknown as McpServer;
+      const secondServer = {
+        registerResource: vi.fn(() => secondRegistration),
+      } as unknown as McpServer;
+      const resource = {
+        uri: 'demo://resource/session/shared-file',
+        name: 'shared-file',
+        mimeType: 'text/plain',
+      };
+
+      registerSessionResource(firstServer, resource, 'text', 'first session');
+      registerSessionResource(secondServer, resource, 'text', 'second session');
+
+      expect(firstRegistration.remove).not.toHaveBeenCalled();
+      expect(secondRegistration.remove).not.toHaveBeenCalled();
+    });
+
+    it('should replace a resource with the same URI on the same server', () => {
+      const firstRegistration = { remove: vi.fn() };
+      const secondRegistration = { remove: vi.fn() };
+      const server = {
+        registerResource: vi
+          .fn()
+          .mockReturnValueOnce(firstRegistration)
+          .mockReturnValueOnce(secondRegistration),
+      } as unknown as McpServer;
+      const resource = {
+        uri: 'demo://resource/session/replaced-file',
+        name: 'replaced-file',
+        mimeType: 'text/plain',
+      };
+
+      registerSessionResource(server, resource, 'text', 'first payload');
+      registerSessionResource(server, resource, 'text', 'second payload');
+
+      expect(firstRegistration.remove).toHaveBeenCalledOnce();
+      expect(secondRegistration.remove).not.toHaveBeenCalled();
+    });
+
     it('should register blob resource correctly', () => {
       const mockServer = {
         registerResource: vi.fn(),

src/everything/resources/session.ts

@@ -6,7 +6,10 @@ import { Resource, ResourceLink } from "@modelcontextprotocol/sdk/types.js";
  * 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>();
+const registeredResources = new WeakMap<
+  McpServer,
+  Map<string, RegisteredResource>
+>();
 
 /**
  * Generates a session-scoped resource URI string based on the provided resource name.
@@ -54,11 +57,16 @@ export const registerSessionResource = (
           blob: payload,
         };
 
-  // Check if a resource with this URI is already registered and remove it
-  const existingResource = registeredResources.get(uri);
+  const serverResources =
+    registeredResources.get(server) ?? new Map<string, RegisteredResource>();
+  registeredResources.set(server, serverResources);
+
+  // Check if a resource with this URI is already registered on this server and remove it
+  const resourceKey = uri.toString();
+  const existingResource = serverResources.get(resourceKey);
   if (existingResource) {
     existingResource.remove();
-    registeredResources.delete(uri);
+    serverResources.delete(resourceKey);
   }
 
   // Register file resource
@@ -74,7 +82,7 @@ export const registerSessionResource = (
   );
 
   // Track the registered resource for potential future removal
-  registeredResources.set(uri, registeredResource);
+  serverResources.set(resourceKey, registeredResource);
 
   return { type: "resource_link", ...resource };
 };