fix: surface list-fetch failures instead of swallowing them

A list load that failed — a transport error, or a result the SDK's era
codec rejects as invalid — reported nothing. The connect-time refresh is
fired with no caller to await it (`void this.refresh()`), so its rejection
became an unhandled rejection: the header said "Connected", the panel
rendered an empty list indistinguishable from a server that has none, and
the failed exchange showed in the Protocol panel as a clean success.

Two surfaces now tell the truth:

- ManagedListState records the failure as observable state (`getError` +
  an `errorChange` event) and still re-throws, so App's auth-recovery
  wrapper keeps working. The four `useManaged*` hooks expose it via a
  shared `useManagedListError`, and the Tools/Prompts/Resources sidebars
  render a `ListLoadError` alert with the reason and a Retry.
- A response the client refused is attributed back to its Protocol entry
  (`markResponseRejected` → `responseRejected` → `MessageEntry.clientError`),
  which now renders an Error status and a "Rejected by the Inspector"
  alert rather than the green resultType badge alone. The SDK gives no
  request id with a decode failure, so the id is recovered by correlation;
  see the comment on `markResponseRejected` for why that is exact.

Also stops `listAllTools` from dropping a failing excluded-tools walk on
the floor — it stays non-fatal but is logged.

Closes #1953

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SW1p8E2uiyyLx4RKwrwSrt

core/react/useManagedResourceTemplates.ts

@@ -6,8 +6,15 @@ import type {
 } from "../mcp/state/managedResourceTemplatesState.js";
 import type { ResourceTemplateType as ResourceTemplate } from "@modelcontextprotocol/client";
 import type { TypedEventGeneric } from "../mcp/typedEventTarget.js";
+import { useManagedListError } from "./useManagedListError.js";
 
 export interface UseManagedResourceTemplatesResult {
+  /**
+   * The last fetch's failure (transport error, or a result the SDK codec
+   * rejected), or `null` when it succeeded. Includes the connect-time load,
+   * whose failure has no caller to surface it (#1953).
+   */
+  error: Error | null;
   resourceTemplates: ResourceTemplate[];
   refresh: () => Promise<ResourceTemplate[]>;
 }
@@ -50,6 +57,8 @@ export function useManagedResourceTemplates(
     };
   }, [managedResourceTemplatesState]);
 
+  const error = useManagedListError(managedResourceTemplatesState);
+
   const refresh = useCallback(async (): Promise<ResourceTemplate[]> => {
     if (!managedResourceTemplatesState || !client) return [];
     // A user-initiated refresh forces a cache-bypassing round trip
@@ -63,5 +72,5 @@ export function useManagedResourceTemplates(
     return next;
   }, [client, managedResourceTemplatesState]);
 
-  return { resourceTemplates, refresh };
+  return { resourceTemplates, error, refresh };
 }