Extensions: advertised-extensions toggle in Server Settings (Phase 2 of #1633) (#1743)

* Extensions: advertised-extensions toggle in Server Settings (Phase 2 of #1633)

Adds the debugging knob from #1633: users choose which extensions the
Inspector advertises to a server, and a server may register different tools
in response. Builds on Phase 1's registry + advertisedExtensions option (#1738).

Settings + persistence (core):
- InspectorServerSettings.advertisedExtensions + StoredMCPServer field, wired
  through serverList's read/write converters and INSPECTOR_FIELD_KEY_MAP
  (omit-when-empty, byte-stable round-trip).
- validateSettings (remote PUT route): isBooleanRecord guard + carry a
  non-empty map; unknown/malformed rejected.
- App.tsx threads savedSettings.advertisedExtensions into the client options.

UI:
- ServerSettingsForm renders an "Advertised Extensions" group of checkboxes
  driven by ADVERTISABLE_EXTENSIONS; a per-server override wins over the
  registry default. Modal folds a toggle into settings.advertisedExtensions.

Test server + proof:
- composable-test-server extensionGatedTools: a tool registered disabled and
  enabled on `initialized` iff the client declared the mapped extension
  (getClientCapabilities). Legacy stateful leg. Threaded through
  load-config/resolve-config; advertised-extensions-http.json showcase + README.
- Integration test connects legacy with/without the tasks extension advertised
  and asserts the gated tool appears/disappears in tools/list — the acceptance
  criterion, proven end to end, not asserted.

Tests: serverList round-trip (non-empty/absent/empty), ServerSettingsForm
toggle rows, ServerSettingsModal fold, validateSettings accept/reject, and the
integration gating test. npm run ci green (per-file ≥90 gate held).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* Extensions: add #1739 proof screenshots (advertised-extensions toggle)

End-to-end smoke test in the web client against the legacy
advertised-extensions-http.json test server (port 3220): connecting with the
Tasks extension advertised (default) lists echo + get_weather, unchecking the
Advertised Extensions → Tasks toggle and reconnecting lists only echo — the
server's tool registration changing on the client-declared extension.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* Extensions: reconverge advertisedExtensions to no-override on default (review)

Address Phase 2 review observation #1: toggling an extension back to its
registry default now deletes the override key (and drops the whole map to
undefined when it empties), so the on-disk `advertisedExtensions` reconverges
to the byte-stable "no override" state instead of persisting a redundant
`{ key: <default> }`. Matches the omit-when-default policy the other settings
use. Only a value that differs from the default is persisted.

Adds a modal test asserting the reconvergence (re-checking the sole disabling
override drops advertisedExtensions to undefined).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/components/groups/ServerSettingsModal/ServerSettingsModal.tsx

@@ -9,6 +9,7 @@ import type {
   ServerType,
 } from "@inspector/core/mcp/types.js";
 import { isOAuthCapableServerType } from "@inspector/core/mcp/config.js";
+import { ADVERTISABLE_EXTENSIONS } from "@inspector/core/mcp/extensions.js";
 import { ListToggle } from "../../elements/ListToggle/ListToggle";
 import {
   ServerSettingsForm,
@@ -176,6 +177,24 @@ export function ServerSettingsModal({
     onSettingsChange({ ...settings, paginatedLists: value });
   }
 
+  function handleAdvertisedExtensionChange(key: string, checked: boolean) {
+    const next = { ...settings.advertisedExtensions };
+    const ext = ADVERTISABLE_EXTENSIONS.find((e) => e.key === key);
+    // Reconverge to "no override" when the toggle returns to the registry
+    // default, so the on-disk map (and its byte-stable round-trip) stays minimal
+    // — matching the omit-when-default policy used for the other settings. Only
+    // a value that actually differs from the default is persisted.
+    if (ext && checked === ext.defaultAdvertised) {
+      delete next[key];
+    } else {
+      next[key] = checked;
+    }
+    onSettingsChange({
+      ...settings,
+      advertisedExtensions: Object.keys(next).length > 0 ? next : undefined,
+    });
+  }
+
   function handleMaxFetchRequestsChange(value: number) {
     onSettingsChange({ ...settings, maxFetchRequests: value });
   }
@@ -251,6 +270,7 @@ export function ServerSettingsModal({
           onTimeoutChange={handleTimeoutChange}
           onAutoRefreshChange={handleAutoRefreshChange}
           onPaginatedListsChange={handlePaginatedListsChange}
+          onAdvertisedExtensionChange={handleAdvertisedExtensionChange}
           onMaxFetchRequestsChange={handleMaxFetchRequestsChange}
           onProtocolEraChange={handleProtocolEraChange}
           onModernLogLevelChange={handleModernLogLevelChange}