test(e2e): subscriptions/listen honored filter narrows against advertised capabilities

Adds an e2e cell on entryModern where the listen filter requests
toolsListChanged + promptsListChanged + resourcesListChanged but the
server advertises only tools.listChanged: honoredFilter on the resolved
McpSubscription is { toolsListChanged: true } and only the tools change
reaches the stream.

A stdio e2e of the modern listen path is not yet feasible without harness
changes (the e2e stdio arms wire the standard child-process
StdioServerTransport, not the serveStdio entry); stdio narrowing is
covered at unit level in serveStdioListen.test.ts. Recorded in the
requirement note.

Author: felixweinberger

test/e2e/requirements.ts

@@ -2684,6 +2684,14 @@ export const REQUIREMENTS: Record<string, Requirement> = {
         transports: ['entryModern'],
         note: 'Hosted by the test body via createMcpHandler so it can publish via handler.notify.'
     },
+    'subscriptions:listen:honored-filter-narrows-to-advertised': {
+        source: 'https://modelcontextprotocol.io/specification/draft/basic/patterns/subscriptions#acknowledgment',
+        behavior:
+            "The acknowledged filter on a subscriptions/listen stream is the requested set narrowed against the server's declared listChanged/subscribe capability bits — a requested type the server does not advertise is dropped from honoredFilter and is never delivered.",
+        addedInSpecVersion: '2026-07-28',
+        transports: ['entryModern'],
+        note: 'Hosted by the test body via createMcpHandler so it can publish via handler.notify. A stdio e2e of the modern listen path is not yet feasible without harness changes (the e2e stdio arms wire the standard child-process StdioServerTransport, not the serveStdio entry); stdio narrowing is covered at unit level in serveStdioListen.test.ts.'
+    },
     'subscriptions:listen:capacity-guard': {
         source: 'sdk',
         behavior:

test/e2e/scenarios/subscriptions.test.ts

@@ -114,6 +114,26 @@ verifies('typescript:subscriptions:listen:legacy-era-steer', async ({ transport
     expect((error as SdkError).message).toContain('resources/subscribe');
 });
 
+verifies('subscriptions:listen:honored-filter-narrows-to-advertised', async () => {
+    // makeServer registers a tool but no prompts/resources: a listen requesting
+    // toolsListChanged + promptsListChanged + resourcesListChanged must come
+    // back honored as toolsListChanged only — the ack reflects only what the
+    // server advertises.
+    await using h = await hostListen();
+    const sub = await h.client.listen({ toolsListChanged: true, promptsListChanged: true, resourcesListChanged: true });
+    expect(sub.honoredFilter).toEqual({ toolsListChanged: true });
+    // And nothing the server doesn't advertise reaches the stream: the entry
+    // delivers via the same narrowed filter it acknowledged.
+    const seen: string[] = [];
+    h.client.setNotificationHandler('notifications/prompts/list_changed', () => void seen.push('prompts'));
+    h.client.setNotificationHandler('notifications/tools/list_changed', () => void seen.push('tools'));
+    h.handler.notify.promptsChanged();
+    h.handler.notify.toolsChanged();
+    await new Promise(r => setTimeout(r, 30));
+    expect(seen).toEqual(['tools']);
+    await sub.close();
+});
+
 verifies('subscriptions:listen:capacity-guard', async () => {
     const handler = createMcpHandler(() => makeServer(), { legacy: 'reject', keepAliveMs: 0, maxSubscriptions: 1 });
     const post = (id: number) =>