fix: address Copilot review round 5 on #2318

RemoteClientTransport keeps its open-stream bookkeeping whether or not
the consumer logs requests, so onFetchStreamUpdate works on its own and
close() can synthesize the terminal update.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01APKSYHGxXBUpnR7ErFiLJn
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/test/integration/mcp/remote/remoteClientTransport-unit.test.ts

@@ -432,6 +432,38 @@ describe("RemoteClientTransport (focused branch coverage)", () => {
       expect(onFetchStreamUpdate).toHaveBeenCalledTimes(1);
     });
 
+    it("synthesizes the close on close() for a consumer that registered only onFetchStreamUpdate", async () => {
+      const onFetchStreamUpdate = vi.fn();
+      const { response, push } = createPushableEventStream();
+      const t = makeTransport(
+        { events: () => response },
+        { onFetchStreamUpdate },
+      );
+      await t.start();
+      push({
+        type: "fetch_request",
+        data: {
+          id: "stream",
+          method: "GET",
+          url: "http://x/mcp",
+          timestamp: new Date().toISOString(),
+          requestHeaders: {},
+          responseStatus: 200,
+          responseHeaders: { "content-type": "text/event-stream" },
+        } as never,
+      });
+      push({
+        type: "fetch_stream_update",
+        data: { id: "stream", eventCount: 3 },
+      });
+      await tick();
+      await t.close();
+      expect(onFetchStreamUpdate).toHaveBeenLastCalledWith("stream", {
+        eventCount: 3,
+        closedAt: expect.any(Date),
+      });
+    });
+
     it("drops fetch_stream_update events when no handler is registered", async () => {
       const onFetchRequest = vi.fn();
       const t = makeTransport(

core/mcp/remote/remoteClientTransport.ts

@@ -552,11 +552,11 @@ export class RemoteClientTransport implements Transport {
               this.resetSseResponseWait(progressToken);
             }
             this.onmessage?.(msg, undefined);
-          } else if (
+          } else if (parsed.type === "fetch_request") {
-            parsed.type === "fetch_request" &&
-            this.options.onFetchRequest
-          ) {
             const entry = parsed.data;
+            // Stream bookkeeping runs whether or not the consumer logs
+            // requests: `onFetchStreamUpdate` is documented to work on its
+            // own, and `close()` needs to know which streams are open.
             if (
               isLongLivedStreamResponse(
                 entry.method,
@@ -565,7 +565,7 @@ export class RemoteClientTransport implements Transport {
             ) {
               this.openStreams.set(entry.id, 0);
             }
-            this.options.onFetchRequest({
+            this.options.onFetchRequest?.({
               ...entry,
               timestamp:
                 typeof entry.timestamp === "string"