fix: address Copilot review round 2 on #2318

- fetchTracking: media types and HTTP methods compare case-insensitively;
  a `Request` input's own method is honoured; the SSE line scanner
  accepts LF, CRLF and a bare CR, holding a trailing CR until the next
  chunk decides whether it is half of a CRLF.
- MessageTrackingTransport does not report a send failure for a request
  the caller aborted through `requestSignal`, and InspectorClient keeps a
  request whose send failed with a request timeout — both are sent,
  unanswered requests, which is the state to keep reporting.
- createTransportNode builds a fetch tracker when any tracking callback
  is supplied, not only `onFetchRequest`.
- RemoteClientTransport's relay wait expires with the SDK's own timeout
  shape, so the web client's relay timeout is annotated like every other.

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/authResyncPropagation.test.ts

@@ -117,7 +117,7 @@ describe("RemoteClientTransport send contract", () => {
     const started = Date.now();
     await expect(
       transport.send({ jsonrpc: "2.0", id: 1, method: "tools/list" }),
-    ).rejects.toThrow(/Timed out waiting for MCP response on SSE/i);
+    ).rejects.toThrow(/Request timed out/);
     expect(Date.now() - started).toBeLessThan(5000);
 
     await transport.close();

clients/web/src/test/core/mcp/fetchTracking.test.ts

@@ -826,6 +826,56 @@ describe("createFetchTracker long-lived stream watching (#2318)", () => {
     expect(last.closedAt).toBeInstanceOf(Date);
   });
 
+  it("accepts bare CR line endings, and a CRLF split across chunks", async () => {
+    const server = controlledStream();
+    const { updates } = await trackStream(server.stream);
+    server.push("data: a\r\rdata: b\r");
+    await flush();
+    // The trailing CR is held: it may be the first half of a CRLF.
+    expect(updates.map((u) => u.stream.eventCount)).toEqual([0, 1]);
+    server.push("\n\r\n");
+    await flush();
+    expect(updates.map((u) => u.stream.eventCount)).toEqual([0, 1, 2]);
+  });
+
+  it("classifies the content type and the method case-insensitively", async () => {
+    const server = controlledStream();
+    const updates: unknown[] = [];
+    const fetcher = createFetchTracker(
+      (async () =>
+        new Response(server.stream, {
+          headers: { "content-type": "Text/Event-Stream" },
+        })) as typeof fetch,
+      { updateStream: (id, state) => updates.push({ id, state }) },
+    );
+    await fetcher("https://example.com/mcp", { method: "get" });
+    expect(updates).toHaveLength(1);
+  });
+
+  it("takes the method from a Request input when init carries none", async () => {
+    // A bounded POST reply must go down the body-capture path, not the
+    // watcher, when the caller passed a `Request` rather than `init`.
+    const bodies: string[] = [];
+    const updates: unknown[] = [];
+    const tracked: FetchRequestEntryBase[] = [];
+    const fetcher = createFetchTracker(
+      (async () =>
+        new Response("data: x\n\n", {
+          headers: { "content-type": "text/event-stream" },
+        })) as typeof fetch,
+      {
+        trackRequest: (entry) => tracked.push(entry),
+        updateResponseBody: (_id, body) => bodies.push(body),
+        updateStream: (id, state) => updates.push({ id, state }),
+      },
+    );
+    await fetcher(new Request("https://example.com/mcp", { method: "POST" }));
+    await flush();
+    expect(tracked[0]?.method).toBe("POST");
+    expect(bodies).toEqual(["data: x\n\n"]);
+    expect(updates).toEqual([]);
+  });
+
   it("reports the close when the server ends the stream", async () => {
     const server = controlledStream();
     const { updates, id } = await trackStream(server.stream);

clients/web/src/test/core/mcp/inspectorClient-diagnostics-callbacks.test.ts

@@ -0,0 +1,75 @@
+import { describe, it, expect } from "vitest";
+import { SdkError, SdkErrorCode } from "@modelcontextprotocol/client";
+import type { JSONRPCRequest } from "@modelcontextprotocol/client";
+import { InspectorClient } from "@inspector/core/mcp/inspectorClient.js";
+import type { MessageTrackingCallbacks } from "@inspector/core/mcp/messageTrackingTransport.js";
+
+/**
+ * The outstanding-request bookkeeping behind the connection diagnostics
+ * (#2318), driven through the message-tracking callbacks the client hands its
+ * transport — the same seam the transport uses, without a connection.
+ */
+describe("InspectorClient diagnostics tracking callbacks", () => {
+  interface Internals {
+    createMessageTrackingCallbacks: () => MessageTrackingCallbacks;
+  }
+
+  function makeClient(): {
+    client: InspectorClient;
+    callbacks: MessageTrackingCallbacks;
+  } {
+    const client = new InspectorClient(
+      { type: "stdio", command: "noop", args: [] },
+      // Never connects; the callbacks are exercised directly.
+      { environment: { transport: () => ({}) as never } },
+    );
+    const callbacks = (
+      client as unknown as Internals
+    ).createMessageTrackingCallbacks();
+    return { client, callbacks };
+  }
+
+  const request = (id: number): JSONRPCRequest => ({
+    jsonrpc: "2.0",
+    id,
+    method: "tools/list",
+  });
+
+  const outstandingIds = (client: InspectorClient) =>
+    client.getConnectionDiagnostics().outstandingRequests.map((r) => r.id);
+
+  it("rolls a request back when its send failed before reaching the wire", () => {
+    const { client, callbacks } = makeClient();
+    callbacks.trackRequest!(request(1), "client");
+    expect(outstandingIds(client)).toEqual([1]);
+    callbacks.trackSendFailure!(request(1), new Error("connection closed"));
+    expect(outstandingIds(client)).toEqual([]);
+  });
+
+  it("keeps a request whose send failed with a request timeout", () => {
+    // The browser's remote transport awaits the response inside `send`, so
+    // its relay timeout surfaces as a send failure — the request reached the
+    // server and is still unanswered.
+    const { client, callbacks } = makeClient();
+    callbacks.trackRequest!(request(1), "client");
+    callbacks.trackSendFailure!(
+      request(1),
+      new SdkError(SdkErrorCode.RequestTimeout, "Request timed out", {
+        timeout: 60_000,
+      }),
+    );
+    expect(outstandingIds(client)).toEqual([1]);
+  });
+
+  it("only tracks client-originated requests, and ignores a rollback for an unknown id", () => {
+    const { client, callbacks } = makeClient();
+    callbacks.trackRequest!(request(7), "server");
+    expect(outstandingIds(client)).toEqual([]);
+    let changes = 0;
+    client.addEventListener("connectionDiagnosticsChange", () => {
+      changes += 1;
+    });
+    callbacks.trackSendFailure!(request(7), new Error("nope"));
+    expect(changes).toBe(0);
+  });
+});

clients/web/src/test/core/mcp/messageTrackingTransport.test.ts

@@ -48,6 +48,18 @@ describe("MessageTrackingTransport.send", () => {
     await expect(failing.send(request)).rejects.toBe(boom);
     expect(callbacks.trackRequest).toHaveBeenCalledWith(request, "client");
     expect(trackSendFailure).toHaveBeenCalledWith(request, boom);
+    // A caller's own abort is a cancellation, not a send failure: the
+    // request may well have reached the server, and stays unanswered.
+    trackSendFailure.mockClear();
+    const controller = new AbortController();
+    controller.abort();
+    await expect(
+      failing.send(
+        { jsonrpc: "2.0", id: 2, method: "tools/call" },
+        { requestSignal: controller.signal },
+      ),
+    ).rejects.toBe(boom);
+    expect(trackSendFailure).not.toHaveBeenCalled();
     // Only requests roll back: a failed notification has no pending entry.
     trackSendFailure.mockClear();
     await expect(

clients/web/src/test/integration/mcp/node/transport.test.ts

@@ -188,6 +188,35 @@ describe("Transport", () => {
       }
     });
 
+    it("tracks fetches when only onFetchResponseBody is supplied (#2318)", async () => {
+      // Any one of the tracking callbacks earns the tracker — a caller that
+      // wants only bodies (or only stream updates) must not be handed the
+      // bare fetch and silently receive nothing.
+      const server = createTestServerHttp({
+        serverInfo: createTestServerInfo(),
+        tools: [createEchoTool()],
+        serverType: "streamable-http",
+      });
+      try {
+        await server.start();
+        const bodies: string[] = [];
+        const result = createTransportNode(
+          { type: "streamable-http", url: server.url },
+          { onFetchResponseBody: (_id, body) => bodies.push(body) },
+        );
+        const client = new Client(
+          { name: "test-client", version: "1.0.0" },
+          { capabilities: {} },
+        );
+        await client.connect(result.transport);
+        await client.listTools();
+        await client.close();
+        expect(bodies.some((body) => body.includes("tools"))).toBe(true);
+      } finally {
+        await server.stop();
+      }
+    });
+
     it("should call onFetchRequest callback for streamable-http transport", async () => {
       const server = createTestServerHttp({
         serverInfo: createTestServerInfo(),

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

@@ -16,6 +16,7 @@ import type { RemoteTransportOptions } from "@inspector/core/mcp/remote/remoteCl
 import type { MCPServerConfig } from "@inspector/core/mcp/types.js";
 import type { RemoteEvent } from "@inspector/core/mcp/remote/types.js";
 import type { JSONRPCMessage } from "@modelcontextprotocol/client";
+import { SdkErrorCode } from "@modelcontextprotocol/client";
 import {
   AuthChallengeError,
   AuthRecoveryRequiredError,
@@ -615,6 +616,27 @@ describe("RemoteClientTransport (focused branch coverage)", () => {
       ).rejects.toThrow(/Transport is closed/);
     });
 
+    it("rejects an expired SSE response wait with the SDK's own timeout shape (#2318)", async () => {
+      // The relay's budget, not the request's, can be the one that expires;
+      // shaped as the SDK's timeout so InspectorClient annotates it the same.
+      const t = makeTransport(
+        {
+          events: () => openEventsResponse(),
+          send: () => jsonResponse({ ok: true }),
+        },
+        { sseResponseTimeoutMs: 50 },
+      );
+      await t.start();
+      await expect(
+        t.send({ jsonrpc: "2.0", id: 1, method: "tools/list" }),
+      ).rejects.toMatchObject({
+        code: SdkErrorCode.RequestTimeout,
+        message: "Request timed out",
+        data: { timeout: 50 },
+      });
+      await t.close();
+    });
+
     it("does not wait for an SSE response on subscriptions/listen (long-lived stream)", async () => {
       // A `subscriptions/listen` never yields a JSON-RPC response — only an
       // acknowledged notification over the event channel — so send() must

core/mcp/fetchTracking.ts

@@ -222,11 +222,13 @@ export function isLongLivedStreamResponse(
   method: string,
   contentType: string | null | undefined,
 ): boolean {
-  if (method !== "GET") return false;
+  if (method.toUpperCase() !== "GET") return false;
   if (!contentType) return false;
+  // Media types are case-insensitive (RFC 9110 §8.3.1); a server may send
+  // `Text/Event-Stream` and still be sending an event stream.
+  const type = contentType.toLowerCase();
   return (
-    contentType.includes("text/event-stream") ||
+    type.includes("text/event-stream") || type.includes("application/x-ndjson")
-    contentType.includes("application/x-ndjson")
   );
 }
 
@@ -261,7 +263,9 @@ export type LongLivedStreamFraming = "sse" | "ndjson";
 export function longLivedStreamFraming(
   contentType: string | null | undefined,
 ): LongLivedStreamFraming {
-  return contentType?.includes("application/x-ndjson") ? "ndjson" : "sse";
+  return contentType?.toLowerCase().includes("application/x-ndjson")
+    ? "ndjson"
+    : "sse";
 }
 
 /**
@@ -314,8 +318,7 @@ function watchLongLivedStream(
   // stream with no state to show — the count only moves on an event.
   update(id, { eventCount });
 
-  const consumeLine = (rawLine: string): void => {
+  const consumeLine = (line: string): void => {
-    const line = rawLine.endsWith("\r") ? rawLine.slice(0, -1) : rawLine;
     if (framing === "ndjson") {
       if (line.trim() === "") return;
       eventCount += 1;
@@ -335,18 +338,35 @@ function watchLongLivedStream(
     if (line === "data" || line.startsWith("data:")) blockHasData = true;
   };
 
+  // Split off every complete line in `pending`. The SSE grammar (and the
+  // SDK's parser) accept LF, CRLF and a bare CR as a line ending, so all three
+  // end a line here; a CR that is the last byte so far is held back, since
+  // the LF of a CRLF pair may still be in flight in the next chunk.
+  const consumeCompleteLines = (): void => {
+    for (;;) {
+      const cr = pending.indexOf("\r");
+      const lf = pending.indexOf("\n");
+      const end = cr === -1 ? lf : lf === -1 ? cr : Math.min(cr, lf);
+      if (end === -1) return;
+      if (pending[end] === "\r") {
+        if (end === pending.length - 1) return;
+        const width = pending[end + 1] === "\n" ? 2 : 1;
+        consumeLine(pending.slice(0, end));
+        pending = pending.slice(end + width);
+      } else {
+        consumeLine(pending.slice(0, end));
+        pending = pending.slice(end + 1);
+      }
+    }
+  };
+
   const pump = async (): Promise<void> => {
     try {
       for (;;) {
         const { value, done } = await reader.read();
         if (done) break;
         pending += decoder.decode(value, { stream: true });
-        let newline = pending.indexOf("\n");
+        consumeCompleteLines();
-        while (newline !== -1) {
-          consumeLine(pending.slice(0, newline));
-          pending = pending.slice(newline + 1);
-          newline = pending.indexOf("\n");
-        }
       }
     } catch {
       // An errored or aborted stream has still ended — fall through to report
@@ -384,7 +404,12 @@ export function createFetchTracker(
         : input instanceof URL
           ? input.toString()
           : input.url;
-    const method = init?.method || "GET";
+    // The method decides the long-lived-stream classification below, so it
+    // has to be the one the request actually carries: a `Request` input
+    // carries its own, and HTTP methods compare case-insensitively.
+    const method = (
+      init?.method ?? (input instanceof Request ? input.method : "GET")
+    ).toUpperCase();
 
     // Extract headers, redacting sensitive values BEFORE they reach any
     // downstream sink (logger, in-memory list, persisted session storage).

core/mcp/inspectorClient.ts

@@ -273,6 +273,7 @@ import {
 import { SdkError, SdkErrorCode } from "@modelcontextprotocol/client";
 import {
   annotateRequestTimeout,
+  isRequestTimeoutError,
   type ConnectionDiagnostics,
   type LastResponse,
   type NotificationStreamState,
@@ -1131,11 +1132,16 @@ export class InspectorClient extends InspectorClientEventTarget {
         };
         this.dispatchTypedEvent("message", entry);
       },
-      trackSendFailure: (message: JSONRPCRequest) => {
+      trackSendFailure: (message: JSONRPCRequest, error: unknown) => {
-        // The frame never reached the wire, so it is not awaiting a response.
+        // A send that failed because the request timed out is not a send
-        // Leaving it would report a request the server never saw as
+        // that failed: the browser's remote transport awaits the response
-        // unanswered, in every timeout message and Connection Info row, until
+        // inside `send`, so its relay timeout surfaces here — the request
-        // the session resets (#2318).
+        // reached the server and went unanswered, which is the state to
+        // keep reporting. Every other failure means the frame never reached
+        // the wire, and leaving it would report a request the server never
+        // saw as unanswered, in every timeout message and Connection Info
+        // row, until the session resets (#2318).
+        if (isRequestTimeoutError(error)) return;
         if (this.outstandingRequests.delete(message.id)) {
           this.dispatchConnectionDiagnosticsChange();
         }

core/mcp/messageTrackingTransport.ts

@@ -29,7 +29,11 @@ export interface MessageTrackingCallbacks {
    * closed, the fetch failed before the frame reached the wire). Fires after
    * `trackRequest` already recorded it, so a consumer keeping "requests still
    * awaiting a response" can roll that entry back — a request that never went
-   * out is not unanswered (#2318).
+   * out is not unanswered (#2318). Not fired when the caller aborted the
+   * request through `requestSignal`: the modern transport aborts an in-flight
+   * request's own stream to cancel it (and the SDK does the same on a
+   * per-request timeout), and a request that was sent and then given up on
+   * is exactly the unanswered kind.
    */
   trackSendFailure?: (message: JSONRPCRequest, error: unknown) => void;
 }
@@ -106,7 +110,9 @@ export class MessageTrackingTransport implements Transport {
         const request = message as JSONRPCRequest;
         this.callbacks.trackRequest?.(request, "client");
         return this.baseTransport.send(message, options).catch((err) => {
-          this.callbacks.trackSendFailure?.(request, err);
+          if (!options?.requestSignal?.aborted) {
+            this.callbacks.trackSendFailure?.(request, err);
+          }
           throw err;
         });
       }

core/mcp/node/transport.ts

@@ -55,6 +55,12 @@ export function createTransportNode(
     interceptAuthChallenges = false,
     onAuthChallengeObserved,
   } = options;
+  // Any of the three tracking callbacks earns a tracker: each is optional on
+  // the tracker itself, and a caller that wants only stream updates (or only
+  // bodies) must not be silently handed the bare fetch (#2318).
+  const wantsFetchTracking = Boolean(
+    onFetchRequest || onFetchResponseBody || onFetchStreamUpdate,
+  );
 
   // `optionsFetchFn` is the caller's whole fetch stack and already sits on top of
   // a proxy-aware base when one is needed — the Node clients install
@@ -115,7 +121,7 @@ export function createTransportNode(
     const sseFetch = configuredSseFetch
       ? withChallengeObserver(configuredSseFetch)
       : fetchWithOptionalAuthIntercept;
-    const trackedFetch = onFetchRequest
+    const trackedFetch = wantsFetchTracking
       ? createFetchTracker(sseFetch, {
           trackRequest: onFetchRequest,
           updateResponseBody: onFetchResponseBody,
@@ -136,7 +142,7 @@ export function createTransportNode(
       ...(headers && { headers }),
     };
 
-    const postFetch = onFetchRequest
+    const postFetch = wantsFetchTracking
       ? createFetchTracker(fetchWithOptionalAuthIntercept, {
           trackRequest: onFetchRequest,
           updateResponseBody: onFetchResponseBody,
@@ -164,7 +170,7 @@ export function createTransportNode(
       ...(headers && { headers }),
     };
 
-    const transportFetch = onFetchRequest
+    const transportFetch = wantsFetchTracking
       ? createFetchTracker(fetchWithOptionalAuthIntercept, {
           trackRequest: onFetchRequest,
           updateResponseBody: onFetchResponseBody,

core/mcp/remote/remoteClientTransport.ts

@@ -11,6 +11,7 @@ import type {
   JSONRPCMessage,
   MessageExtraInfo,
 } from "@modelcontextprotocol/client";
+import { SdkError, SdkErrorCode } from "@modelcontextprotocol/client";
 import type { InspectorServerSettings, StderrLogEntry } from "../types.js";
 import type { FetchRequestEntryBase, FetchStreamState } from "../types.js";
 import type {
@@ -689,10 +690,17 @@ export class RemoteClientTransport implements Transport {
     return new Promise((resolve, reject) => {
       const timer = setTimeout(() => {
         this.sseResponseWaits.delete(requestId);
+        // The SDK's own per-request timeout shape, not a plain `Error`: this
+        // wait can expire before the SDK's timer does (its budget is the
+        // relay's, not the request's), and the rejection travels up through
+        // `Client.request`, where `InspectorClient` annotates a timeout of
+        // exactly this shape with the connection's state (#2318). A plain
+        // error would pass that decorator untouched and reach the user as a
+        // bare timeout on the web client alone.
         reject(
-          new Error(
+          new SdkError(SdkErrorCode.RequestTimeout, "Request timed out", {
-            `Timed out waiting for MCP response on SSE (${this.sseResponseTimeoutMs}ms)`,
+            timeout: this.sseResponseTimeoutMs,
-          ),
+          }),
         );
       }, this.sseResponseTimeoutMs);
       this.sseResponseWaits.set(requestId, {