feat(core): report connection state on a request timeout (#2318)

A request timeout used to surface as a bare `Request timed out`. Every
fact needed to explain it was already in-process: what the client was
still waiting on, when it last heard back, and the state of the
standalone GET notification stream. The SDK's timeout now rejects with
all three, and the same snapshot is shown live in Connection Info and
on the Network entry for the stream.

- core/mcp/connectionDiagnostics.ts: the snapshot type, its one-line
  description, and `annotateRequestTimeout`, which rebuilds the SDK's
  per-request timeout with the state at that moment.
- InspectorClient decorates the SDK Client's `request` (the one funnel
  every verb goes through) so the annotation covers the whole surface;
  tracks outstanding requests with their send time, the last response,
  and the most recent long-lived transport stream; exposes
  `getConnectionDiagnostics()` and `connectionDiagnosticsChange`.
- fetchTracking watches a long-lived stream through a tee'd clone,
  counting SSE events and reporting the close, via a new
  `updateStream` callback wired through the node transport, the remote
  session (`fetch_stream_update`), and the browser transport.
- FetchRequestLogState patches `entry.stream`; the Network entry's
  placeholder reports the event count and open/closed state.
- Connection Info gains a Connection Activity section, ticking while
  open (`useTickingClock`).

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/react/useInspectorClient.ts

@@ -12,6 +12,7 @@ import type {
 } from "@modelcontextprotocol/client";
 import type { ExcludedTool } from "../mcp/types.js";
 import type { MalformedListItem } from "../mcp/listSalvage.js";
+import type { ConnectionDiagnostics } from "../mcp/connectionDiagnostics.js";
 import { useStoreSnapshot } from "./useStoreSnapshot.js";
 
 // Module-scope frozen object so the `?? EMPTY_CLIENT_CAPABILITIES`
@@ -27,6 +28,13 @@ const EMPTY_CLIENT_CAPABILITIES: ClientCapabilities = Object.freeze({});
  */
 const NO_EXCLUDED_TOOLS: ExcludedTool[] = [];
 const NO_MALFORMED_LIST_ITEMS: MalformedListItem[] = [];
+// Also the fallback for a client that does not implement the optional
+// accessor (a test double), so the field is always a snapshot and never
+// `undefined` — one shape for consumers, whatever client is attached.
+const NO_CONNECTION_DIAGNOSTICS: ConnectionDiagnostics = Object.freeze({
+  capturedAt: 0,
+  outstandingRequests: [],
+});
 
 const readStatus = (client: InspectorClientProtocol): ConnectionStatus =>
   client.getStatus();
@@ -53,6 +61,10 @@ const readExcludedTools = (client: InspectorClientProtocol): ExcludedTool[] =>
 const readMalformedListItems = (
   client: InspectorClientProtocol,
 ): MalformedListItem[] => client.getMalformedListItems();
+const readConnectionDiagnostics = (
+  client: InspectorClientProtocol,
+): ConnectionDiagnostics =>
+  client.getConnectionDiagnostics?.() ?? NO_CONNECTION_DIAGNOSTICS;
 
 export interface UseInspectorClientResult {
   status: ConnectionStatus;
@@ -86,6 +98,13 @@ export interface UseInspectorClientResult {
    * non-empty set means that list rendered without them (#1909).
    */
   malformedListItems: MalformedListItem[];
+  /**
+   * What the client is still waiting on, when it last heard back, and the
+   * state of the notification stream — re-read on every request, response
+   * and stream event. The Connection Info modal renders it; a request
+   * timeout's message is written from the same snapshot (#2318).
+   */
+  connectionDiagnostics: ConnectionDiagnostics;
   /**
    * Message from the most recent mid-session transport failure (the client's
    * `error` event — stdio crash, SSE drop, HTTP 5xx). Stays set until the next
@@ -174,6 +193,12 @@ export function useInspectorClient(
     readMalformedListItems,
     NO_MALFORMED_LIST_ITEMS,
   );
+  const connectionDiagnostics = useStoreSnapshot(
+    inspectorClient,
+    "connectionDiagnosticsChange",
+    readConnectionDiagnostics,
+    NO_CONNECTION_DIAGNOSTICS,
+  );
 
   // `lastError` is the one value here that is NOT a snapshot of something the
   // client stores: there is no `getLastError()`, because the client emits the
@@ -243,6 +268,7 @@ export function useInspectorClient(
     discoverResult,
     excludedTools,
     malformedListItems,
+    connectionDiagnostics,
     lastError,
     appRendererClient: inspectorClient?.getAppRendererClient() ?? null,
     connect,