fix: address Copilot review round 4 on #2318

- fetchTracking: one non-throwing reporter fronts every stream update —
  the open (inside the fetch wrapper), each coalesced count (from a
  timer) and the close (off the discarded watcher).
- rawWireRequest annotates a request timeout its transport's send
  rejects with, so the browser's relay timeout on a raw-wire call reads
  like every other.
- RemoteClientTransport reports still-open streams closed on close(),
  since the backend watcher's own close cannot reach a channel that the
  disconnect has already torn down.

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/core/mcp/fetchTracking.test.ts

@@ -934,6 +934,28 @@ describe("createFetchTracker long-lived stream watching (#2318)", () => {
     expect(updates.at(-1)!.stream.closedAt).toBeInstanceOf(Date);
   });
 
+  it("returns the response even when the listener throws on the open report", async () => {
+    // The open is reported synchronously inside the fetch wrapper; a throw
+    // there must not turn a successful response into a rejected fetch.
+    const server = controlledStream();
+    const response = new Response(server.stream, {
+      headers: { "content-type": "text/event-stream" },
+    });
+    const fetcher = createFetchTracker((async () => response) as typeof fetch, {
+      updateStream: () => {
+        throw new Error("sink closed");
+      },
+      streamUpdateIntervalMs: 0,
+    });
+    await expect(
+      fetcher("https://example.com/mcp", { method: "GET" }),
+    ).resolves.toBe(response);
+    // ...and a throw from a coalesced count does not escape the timer either.
+    server.push("data: a\n\n");
+    server.end();
+    await flush();
+  });
+
   it("survives a stream-update listener that throws on the close", async () => {
     // The watcher's promise is discarded, so a throw from the final report
     // would otherwise be an unhandled rejection — which fails the whole run.

clients/web/src/test/core/mcp/inspectorClient-raw-wire.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi } from "vitest";
-import { SdkErrorCode } from "@modelcontextprotocol/client";
+import { SdkError, SdkErrorCode } from "@modelcontextprotocol/client";
 import { InspectorClient } from "@inspector/core/mcp/inspectorClient.js";
 import { ModernGetTaskResultSchema } from "@inspector/core/mcp/modernTaskSchemas.js";
 
@@ -151,6 +151,46 @@ describe("InspectorClient raw-wire channel (#1631)", () => {
     }
   });
 
+  it("annotates a request timeout the transport's send rejects with (#2318)", async () => {
+    // The browser's remote transport awaits the response inside `send`, so
+    // its relay wait can expire before the local timer; it arrives here as
+    // the SDK's timeout shape and gets the same annotation.
+    const client = makeClient();
+    internals(client).transport = {
+      send: vi.fn().mockRejectedValue(
+        new SdkError(SdkErrorCode.RequestTimeout, "Request timed out", {
+          timeout: 60_000,
+        }),
+      ),
+    };
+    await expect(
+      internals(client).rawWireRequest(
+        "tasks/get",
+        {},
+        ModernGetTaskResultSchema,
+      ),
+    ).rejects.toMatchObject({
+      code: SdkErrorCode.RequestTimeout,
+      message: expect.stringMatching(
+        /^Request timed out after 1m00s \(tasks\/get\)\. /,
+      ),
+      data: expect.objectContaining({ timeout: 60_000, method: "tasks/get" }),
+    });
+  });
+
+  it("leaves a non-timeout send failure untouched", async () => {
+    const client = makeClient();
+    const boom = new Error("connection closed");
+    internals(client).transport = { send: vi.fn().mockRejectedValue(boom) };
+    await expect(
+      internals(client).rawWireRequest(
+        "tasks/get",
+        {},
+        ModernGetTaskResultSchema,
+      ),
+    ).rejects.toBe(boom);
+  });
+
   it("rejects all pending requests on teardown", async () => {
     const client = makeClient();
     internals(client).transport = {

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

@@ -375,6 +375,63 @@ describe("RemoteClientTransport (focused branch coverage)", () => {
       });
     });
 
+    it("reports a still-open stream closed on close(), since the backend's own close cannot arrive (#2318)", async () => {
+      const onFetchStreamUpdate = vi.fn();
+      const { response, push } = createPushableEventStream();
+      const t = makeTransport(
+        { events: () => response },
+        { onFetchStreamUpdate, onFetchRequest: vi.fn() },
+      );
+      await t.start();
+      const entry = (id: string, method: string, contentType: string) =>
+        ({
+          id,
+          method,
+          url: "http://x/mcp",
+          timestamp: new Date().toISOString(),
+          requestHeaders: {},
+          responseStatus: 200,
+          responseHeaders: { "Content-Type": contentType },
+        }) as never;
+      push({
+        type: "fetch_request",
+        data: entry("stream", "GET", "text/event-stream"),
+      });
+      push({
+        type: "fetch_request",
+        data: entry("post", "POST", "text/event-stream"),
+      });
+      push({
+        type: "fetch_stream_update",
+        data: { id: "stream", eventCount: 2 },
+      });
+      push({
+        type: "fetch_request",
+        data: entry("earlier", "GET", "text/event-stream"),
+      });
+      push({
+        type: "fetch_stream_update",
+        data: {
+          id: "earlier",
+          eventCount: 1,
+          closedAt: new Date().toISOString(),
+        },
+      });
+      await tick();
+      onFetchStreamUpdate.mockClear();
+      await t.close();
+      // Only the stream still open is reported closed, with its last count;
+      // the bounded POST and the already-closed stream are not.
+      expect(onFetchStreamUpdate).toHaveBeenCalledTimes(1);
+      expect(onFetchStreamUpdate).toHaveBeenCalledWith("stream", {
+        eventCount: 2,
+        closedAt: expect.any(Date),
+      });
+      // A second close reports nothing more.
+      await t.close();
+      expect(onFetchStreamUpdate).toHaveBeenCalledTimes(1);
+    });
+
     it("drops fetch_stream_update events when no handler is registered", async () => {
       const onFetchRequest = vi.fn();
       const t = makeTransport(