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>

core/mcp/fetchTracking.ts

@@ -310,8 +310,21 @@ function watchLongLivedStream(
   framing: LongLivedStreamFraming,
   callbacks: FetchTrackingCallbacks,
 ): void {
-  const report = callbacks.updateStream;
-  if (!report) return;
+  const listener = callbacks.updateStream;
+  if (!listener) return;
+  // Every report goes through here: the listener is consumer code (a relay
+  // sink that may already be closed, a state store), and it runs from three
+  // places none of which may throw outward — synchronously inside the fetch
+  // wrapper (the open), from a timer (a coalesced count), and off the
+  // discarded watcher promise (the close). A throw is the listener's
+  // problem; the stream's bookkeeping carries on.
+  const report = (state: FetchStreamState): void => {
+    try {
+      listener(id, state);
+    } catch {
+      // See above.
+    }
+  };
   const intervalMs =
     callbacks.streamUpdateIntervalMs ?? DEFAULT_STREAM_UPDATE_INTERVAL_MS;
   let body: ReadableStream<Uint8Array> | null;
@@ -333,19 +346,19 @@ function watchLongLivedStream(
   let reportTimer: ReturnType<typeof setTimeout> | null = null;
   const reportCount = (): void => {
     if (intervalMs <= 0) {
-      report(id, { eventCount });
+      report({ eventCount });
       return;
     }
     if (reportTimer !== null) return;
     reportTimer = setTimeout(() => {
       reportTimer = null;
-      report(id, { eventCount });
+      report({ eventCount });
     }, intervalMs);
   };
   // Announce the stream as open before a byte arrives. A stream that never
   // delivers anything is the #2187 tell, and it would otherwise be the one
   // stream with no state to show — the count only moves on an event.
-  report(id, { eventCount });
+  report({ eventCount });
 
   const consumeLine = (line: string): void => {
     if (framing === "ndjson") {
@@ -410,17 +423,12 @@ function watchLongLivedStream(
       clearTimeout(reportTimer);
       reportTimer = null;
     }
-    try {
-      report(id, { eventCount, closedAt: new Date() });
-    } catch {
-      // A listener that throws must not become an unhandled rejection off a
-      // promise nothing awaits; the stream is closed either way.
-    }
+    report({ eventCount, closedAt: new Date() });
   };
   // Deliberately not awaited: the fetch wrapper has to return the response
   // now, and this watcher lives as long as the stream does. It owns its own
-  // failures — the read loop and the final report are each wrapped in a
-  // `try` — so the promise cannot reject.
+  // failures — the read loop is wrapped in a `try`, and every report goes
+  // through the non-throwing `report` above — so the promise cannot reject.
   void pump();
 }
 

core/mcp/inspectorClient.ts

@@ -2980,7 +2980,17 @@ export class InspectorClient extends InspectorClientEventTarget {
           clearTimeout(pending.timer);
           this.pendingRawWireRequests.delete(id);
         }
-        reject(err instanceof Error ? err : new Error(String(err)));
+        // The browser's remote transport awaits the response inside `send`,
+        // so its relay wait can expire here first, as the SDK's timeout
+        // shape; annotate it exactly as the local timer above does (a
+        // non-timeout error passes through untouched).
+        reject(
+          annotateRequestTimeout(
+            err instanceof Error ? err : new Error(String(err)),
+            method,
+            this.getConnectionDiagnostics(),
+          ),
+        );
       });
     });
     return resultSchema.parse(raw);

core/mcp/remote/remoteClientTransport.ts

@@ -12,6 +12,7 @@ import type {
   MessageExtraInfo,
 } from "@modelcontextprotocol/client";
 import { SdkError, SdkErrorCode } from "@modelcontextprotocol/client";
+import { findHeader, isLongLivedStreamResponse } from "../fetchTracking.js";
 import type { InspectorServerSettings, StderrLogEntry } from "../types.js";
 import type { FetchRequestEntryBase, FetchStreamState } from "../types.js";
 import type {
@@ -265,6 +266,14 @@ export class RemoteClientTransport implements Transport {
   private eventStreamConsumeTask: Promise<void> | null = null;
   private restartingEventStream = false;
   private closed = false;
+  /**
+   * Long-lived streams the backend has reported open, by fetch entry id, with
+   * the last event count seen for each. `close()` reports them closed
+   * itself: it aborts the event channel before asking the backend to
+   * disconnect, so the backend watcher's own close report lands on an
+   * unconsumed queue and is lost with the session (#2318).
+   */
+  private openStreams = new Map<string, number>();
   private readonly sseResponseWaits = new Map<
     string | number,
     SseResponseWait
@@ -548,6 +557,14 @@ export class RemoteClientTransport implements Transport {
             this.options.onFetchRequest
           ) {
             const entry = parsed.data;
+            if (
+              isLongLivedStreamResponse(
+                entry.method,
+                findHeader(entry.responseHeaders, "content-type"),
+              )
+            ) {
+              this.openStreams.set(entry.id, 0);
+            }
             this.options.onFetchRequest({
               ...entry,
               timestamp:
@@ -568,6 +585,10 @@ export class RemoteClientTransport implements Transport {
             this.options.onFetchStreamUpdate
           ) {
             const { id, eventCount, closedAt } = parsed.data;
+            if (closedAt !== undefined) this.openStreams.delete(id);
+            else if (this.openStreams.has(id)) {
+              this.openStreams.set(id, eventCount);
+            }
             this.options.onFetchStreamUpdate(id, {
               eventCount,
               ...(closedAt !== undefined && { closedAt: new Date(closedAt) }),
@@ -856,6 +877,13 @@ export class RemoteClientTransport implements Transport {
     this.closed = true;
     this.cancelAllSseWaits(new Error("Transport closed"));
     await this.stopEventStream();
+    // The disconnect below ends every stream the backend still holds open,
+    // and its close reports cannot reach us any more (see `openStreams`).
+    const closedAt = new Date();
+    for (const [id, eventCount] of this.openStreams) {
+      this.options.onFetchStreamUpdate?.(id, { eventCount, closedAt });
+    }
+    this.openStreams.clear();
 
     if (this._sessionId) {
       try {