fix(apps): address review of app-rendered elicitations

Eight findings from the Copilot review, all accepted.

Ownership across connections was the substantive one, in three parts. A
mid-session transport close reaches teardown only through
`clearAndAnnouncePendingPeerRequests`, whose emptiness check looked at the
native queues alone — so a lone app elicitation survived a dropped connection
with its modal still open; the check now counts the active set too. The web
bridge factory resolves its client at call time, so an entry queued by a
replaced `InspectorClient` could rebuild against the *next* one and answer
through a different server; the host now drops every entry synchronously on
the swap (`AppElicitationController.failAll`) rather than racing core's
awaited teardown. And the request id was only monotonic within one client, so
each replacement client's first request was `app-elicitation-1` — settling
that id could resolve the wrong server's request. It now carries a
per-instance prefix.

Result validation now parses the whole value with `ElicitResultSchema` before
the requested-schema check, instead of inspecting `action` by hand: a
`{ action: "decline", content: { x: {} } }` used to pass, though the standard
result permits only primitives and string arrays in `content`.

The dialog's accessible name now includes the request id and the prompt — two
concurrent elicitations can be for the same app URI, and the previous name
made those indistinguishable, which is what the comment beside it claimed to
prevent.

`observeAppCapabilities` takes a minimal structural `onmessage` contract
(generic over the message type, since a handler typed for a narrower message
is not assignable to one typed for `unknown`), removing the double cast at the
call site.

`smoke:web:elicit` now fails on an uncaught page error after a successful
drive, and captures the async half of that class off the console channel, as
its two sibling smokes do — it could otherwise print OK over a broken bundle.

Adds the tests each fix needs, including the two the review asked for
directly: that `advertiseElicitation` reaches the `AppBridge` constructor, and
that it is absent by default.

Signed-off-by: cliffhall <cliff@futurescale.com>

core/mcp/appElicitation.ts

@@ -6,6 +6,7 @@ import type {
   jsonSchemaValidator,
   ServerCapabilities,
 } from "@modelcontextprotocol/client";
+import { ElicitResultSchema } from "@modelcontextprotocol/core";
 import { MCP_APP_MIME_TYPE, UI_EXTENSION_KEY } from "./extensions.js";
 
 /**
@@ -149,8 +150,13 @@ export function isFormElicitation(params: ElicitRequest["params"]): boolean {
   return mode === undefined || mode === "form";
 }
 
-/** The three actions a completed elicitation may report. */
-const ELICIT_ACTIONS = ["accept", "decline", "cancel"] as const;
+/**
+ * The result contract a completed elicitation must satisfy — the standard MCP
+ * one, not a hand-rolled subset. Checking `action` by hand would accept, for
+ * instance, `{ action: "decline", content: { x: {} } }`, whose content the
+ * schema forbids, and hand the server a result it can reject.
+ */
+const ELICIT_RESULT_ERROR = "App returned an invalid elicitation result";
 
 /**
  * Validates what an app returned before it is handed back to the server.
@@ -170,16 +176,13 @@ export function validateAppElicitResult(
   params: ElicitRequest["params"],
   result: ElicitResult,
 ): string | undefined {
-  if (typeof result !== "object" || result === null) {
-    return "App returned a non-object elicitation result";
-  }
-  const action = (result as { action?: unknown }).action;
-  if (!ELICIT_ACTIONS.includes(action as (typeof ELICIT_ACTIONS)[number])) {
-    return `App returned an unknown elicitation action: ${JSON.stringify(action)}`;
+  const parsed = ElicitResultSchema.safeParse(result);
+  if (!parsed.success) {
+    return `${ELICIT_RESULT_ERROR}: ${parsed.error.issues[0]?.message ?? "does not match ElicitResult"}`;
   }
   // decline / cancel carry no content — they are complete as they stand.
-  if (action !== "accept") return undefined;
-  const content = (result as { content?: unknown }).content;
+  if (parsed.data.action !== "accept") return undefined;
+  const content = parsed.data.content;
   if (
     typeof content !== "object" ||
     content === null ||

core/mcp/inspectorClient.ts

@@ -584,6 +584,17 @@ export class InspectorClient extends InspectorClientEventTarget {
    * elicitations cannot resolve through each other's bridges.
    */
   private appElicitationSeq = 0;
+  /**
+   * Per-instance prefix for {@link appElicitationSeq}.
+   *
+   * A counter alone is not enough: a host may hold ONE renderer across
+   * replacement clients (the web client rebuilds its `InspectorClient` on a
+   * settings change), and every fresh instance would otherwise mint
+   * `app-elicitation-1` for its first request. Settling that id would then
+   * resolve — or discard — whichever connection's request the host happened to
+   * be keying.
+   */
+  private readonly appElicitationPrefix = `app-elicitation-${globalThis.crypto?.randomUUID?.() ?? Math.random().toString(36).slice(2)}`;
   /**
    * Abort controllers for app-rendered elicitations still awaiting an answer.
    * Aborted alongside the native pending queue on disconnect, so a rendered app
@@ -1755,7 +1766,12 @@ export class InspectorClient extends InspectorClientEventTarget {
   private clearAndAnnouncePendingPeerRequests(): void {
     if (
       this.pendingSamples.length === 0 &&
-      this.pendingElicitations.length === 0
+      this.pendingElicitations.length === 0 &&
+      // App-rendered elicitations (#1854) are not in either array — they live in
+      // the host's renderer — so an emptiness check that ignores them lets a
+      // mid-session close (the `onclose` route, which reaches teardown only
+      // through here) leave a modal open for a connection that is gone.
+      this.activeAppElicitations.size === 0
     ) {
       return;
     }
@@ -2946,7 +2962,7 @@ export class InspectorClient extends InspectorClientEventTarget {
     this.activeAppElicitations.add(controller);
     try {
       const result = await renderer({
-        requestId: `app-elicitation-${++this.appElicitationSeq}`,
+        requestId: `${this.appElicitationPrefix}-${++this.appElicitationSeq}`,
         resourceUri,
         params: request.params,
         signal: controller.signal,