callstack
diff --git a/‎CHANGELOG.md‎
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diff --git a/‎src/mcp/__tests__/protocol-era.test.ts‎
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@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- `agent-device mcp` now serves the stateless MCP `2026-07-28` revision alongside the handshake-based revisions it already spoke, as the spec's "dual-era server". Modern clients probe `server/discover`, which advertises the supported revisions, the tools capability, and server identity; their requests declare a protocol version in `_meta`, and their results carry `resultType: "complete"` plus `_meta["io.modelcontextprotocol/serverInfo"]`. `tools/list` and `server/discover` now return the `ttlMs`/`cacheScope` cache hints, so a client can cache the 55-tool, ~223KB tool list for an hour instead of re-fetching it on every start; the list was already emitted in a deterministic (sorted) order, which is the other half of what makes it cacheable. Each revision is answered on its own wire contract: a request declaring `2025-11-25` or `2025-06-18` through modern framing still gets the legacy result shape, and `initialize` never agrees to `2026-07-28`, which has no handshake to establish. A declared revision this server does not implement is rejected with `UnsupportedProtocolVersionError` (`-32022`) naming the ones it does, rather than being served under a version the client did not ask for, and modern framing that omits its required `protocolVersion`/`clientCapabilities` metadata — or supplies a `clientInfo` that is not a valid `Implementation` — is rejected as invalid params. `initialize` and `ping` were removed in `2026-07-28`, so a modern-framed call to either is answered `-32601` rather than served inside a `resultType: "complete"` envelope. Responses to legacy clients are unchanged byte-for-byte — `initialize` and `ping` are still served, and no cache, `resultType`, or `_meta` field is added to their results. Nothing here affects the CLI, Node, or daemon surfaces: the stdio transport, the tool set, and every tool's input/output schema are untouched.
+- Fixed: the MCP `initialize` handshake now answers with the protocol revision the client requested when it is one this server implements, instead of always answering `2025-11-25`. A client pinned to `2025-06-18` was told to speak a revision it had not asked for, which the lifecycle contract answers by disconnecting.
 - `agent-device help workflow` is now a compact ~8KB card instead of a ~41KB dump; the same depth still exists, split into `help scripting` (save-script, secret-safe fills, batch JSON, replay divergence/repair, recording) and `help gestures` (multi-touch shapes and platform quirks), plus a few paragraphs folded into the topics that already owned the subject (`help debugging`, `help physical-device`, `help validate`). Every `help <topic>` first line is now `agent-device <version> — <topic>` so an agent can read the installed version from its mandatory first help read instead of a separate `agent-device --version` call.
 - Cloud iOS (BrowserStack, AWS Device Farm): `snapshot` and `diff` no longer fail with `SESSION_NOT_FOUND` on a live provider session (#1658). The app-session guard they ran belongs to the local XCUITest runner, which must attach to a target app; a cloud capture reads the provider's own driver session and needs no app identity, so the guard now applies to local Apple targets only. Relatedly, a cloud iOS `open com.example.app` now records that bundle id on the session — the provider path skips local app resolution (no simctl/devicectl reaches a hosted device), and used to drop an explicitly spelled bundle id along with it, leaving the session with no app identity at all. Opening a second bundle id replaces the first, matching the local path, where an explicitly spelled target always wins over the session's current app; deep links, display names, and bare `open` still keep the app already tracked.
 - Cloud `fill` (BrowserStack, AWS Device Farm) now witnesses that the field it tapped actually holds text-entry focus before sending its keys, instead of dispatching tap and keys in back-to-back requests (#1658). A WebView input — an OAuth/SSO page in a Safari view controller, for example — takes first responder asynchronously, so the keys used to land with nothing focused while `fill` still answered "Filled N chars"; tapping and filling as two separate commands worked only because the round trip between them gave the field time to focus. The witness is the focused element's own geometry: `fill` polls the active element and proceeds only once it contains the point it tapped, which is the one signal that identifies *which* field took focus. Keyboard visibility cannot — it reads the same before and after a second fill into an already-open form, so it could not tell a focused password field from the email field the previous fill left focused. The response discloses `textEntryReadiness`: `focused-element`, or `keyboard-shown` when the driver has no active-element route but the keyboard rose from hidden after the tap. Both describe a fill that witnessed focus before typing; there is deliberately no value for typing without evidence, because nothing renders this field and such a value would reach a caller as an ordinary success. Breaking: when focus cannot be witnessed, cloud `fill` now FAILS with `COMMAND_FAILED` / `text_entry_focus_not_observed` and sends no keys, instead of typing into whatever holds first responder and answering "Filled N chars" — a fill with no witness must not read as a filled field. That covers a tap that focused nothing, a keyboard already up on a driver that cannot name the focused field, and a driver that reports neither (`text_entry_focus_unobservable`, which points at `press` + `type` as the deliberate way to enter text unwitnessed). Only a positively classified unimplemented route counts as unsupported, so a dead session, an auth rejection, or a grid outage surfaces instead of degrading into a blind text entry.
 
@@ -0,0 +1,203 @@
+import assert from 'node:assert/strict';
+import { test } from 'vitest';
+import {
+  cacheFields,
+  finalizeResult,
+  isMethodRemovedInEra,
+  LEGACY_PROTOCOL_VERSIONS,
+  MODERN_PROTOCOL_VERSION,
+  MODERN_PROTOCOL_VERSIONS,
+  negotiateLegacyProtocolVersion,
+  PREFERRED_LEGACY_PROTOCOL_VERSION,
+  resolveProtocolEra,
+  UnsupportedProtocolVersionError,
+} from '../protocol-era.ts';
+
+const modernMeta = (version: string = MODERN_PROTOCOL_VERSION) => ({
+  _meta: {
+    'io.modelcontextprotocol/protocolVersion': version,
+    'io.modelcontextprotocol/clientCapabilities': {},
+  },
+});
+
+test('initialize echoes a revision the client asked for instead of overriding it', () => {
+  // A client pinned to 2025-06-18 that is answered with a different revision is told to
+  // disconnect by the legacy lifecycle contract.
+  assert.equal(negotiateLegacyProtocolVersion({ protocolVersion: '2025-06-18' }), '2025-06-18');
+  assert.equal(
+    negotiateLegacyProtocolVersion({ protocolVersion: PREFERRED_LEGACY_PROTOCOL_VERSION }),
+    PREFERRED_LEGACY_PROTOCOL_VERSION,
+  );
+});
+
+test('initialize falls back to the newest legacy revision for versions we do not implement', () => {
+  assert.equal(
+    negotiateLegacyProtocolVersion({ protocolVersion: '2024-11-05' }),
+    PREFERRED_LEGACY_PROTOCOL_VERSION,
+  );
+  assert.equal(negotiateLegacyProtocolVersion({}), PREFERRED_LEGACY_PROTOCOL_VERSION);
+  assert.equal(negotiateLegacyProtocolVersion(undefined), PREFERRED_LEGACY_PROTOCOL_VERSION);
+});
+
+test('initialize never agrees to a modern revision, which has no handshake to establish', () => {
+  for (const version of MODERN_PROTOCOL_VERSIONS) {
+    assert.equal(
+      negotiateLegacyProtocolVersion({ protocolVersion: version }),
+      PREFERRED_LEGACY_PROTOCOL_VERSION,
+    );
+  }
+});
+
+test('the declared revision picks the era, so 2025 stays on the legacy wire contract', () => {
+  assert.equal(resolveProtocolEra('tools/list', modernMeta()), 'modern');
+  for (const version of LEGACY_PROTOCOL_VERSIONS) {
+    assert.equal(resolveProtocolEra('tools/list', modernMeta(version)), 'legacy');
+  }
+  assert.equal(resolveProtocolEra('tools/list', {}), 'legacy');
+  assert.equal(resolveProtocolEra('tools/list', undefined), 'legacy');
+});
+
+test('server/discover requires modern request metadata rather than being promoted', () => {
+  assert.equal(resolveProtocolEra('server/discover', modernMeta()), 'modern');
+  // No declared revision: malformed, not an invitation to guess the era.
+  assert.throws(() => resolveProtocolEra('server/discover', undefined), /protocolVersion/);
+  assert.throws(() => resolveProtocolEra('server/discover', { _meta: {} }), /protocolVersion/);
+  // The RPC does not exist in any legacy revision.
+  assert.throws(
+    () => resolveProtocolEra('server/discover', modernMeta(PREFERRED_LEGACY_PROTOCOL_VERSION)),
+    UnsupportedProtocolVersionError,
+  );
+});
+
+test('a declared revision without client capabilities is malformed', () => {
+  assert.throws(
+    () =>
+      resolveProtocolEra('tools/call', {
+        _meta: { 'io.modelcontextprotocol/protocolVersion': MODERN_PROTOCOL_VERSION },
+      }),
+    /clientCapabilities/,
+  );
+  assert.throws(
+    () =>
+      resolveProtocolEra('tools/call', {
+        _meta: {
+          'io.modelcontextprotocol/protocolVersion': MODERN_PROTOCOL_VERSION,
+          'io.modelcontextprotocol/clientCapabilities': 'not-an-object',
+        },
+      }),
+    /clientCapabilities/,
+  );
+});
+
+test('an unimplemented declared revision is rejected with the supported list', () => {
+  assert.throws(
+    () => resolveProtocolEra('tools/call', modernMeta('1900-01-01')),
+    (error: unknown) => {
+      assert.ok(error instanceof UnsupportedProtocolVersionError);
+      assert.equal(error.data.requested, '1900-01-01');
+      assert.ok(error.data.supported.includes(MODERN_PROTOCOL_VERSION));
+      return true;
+    },
+  );
+});
+
+test('a supplied clientInfo must be an Implementation, but omitting it is fine', () => {
+  const withClientInfo = (clientInfo: unknown) => ({
+    _meta: {
+      'io.modelcontextprotocol/protocolVersion': MODERN_PROTOCOL_VERSION,
+      'io.modelcontextprotocol/clientCapabilities': {},
+      'io.modelcontextprotocol/clientInfo': clientInfo,
+    },
+  });
+
+  const valid = { name: 'c', version: '1' };
+  assert.equal(resolveProtocolEra('tools/list', modernMeta()), 'modern');
+  assert.equal(resolveProtocolEra('tools/list', withClientInfo(valid)), 'modern');
+  // Required means present and a string, not non-empty: the schema sets no minimum
+  // length on `name`/`version`, nor on `Icon.src`.
+  assert.equal(
+    resolveProtocolEra('tools/list', withClientInfo({ name: '', version: '' })),
+    'modern',
+  );
+  assert.equal(
+    resolveProtocolEra('tools/list', withClientInfo({ ...valid, icons: [{ src: '' }] })),
+    'modern',
+  );
+  // Every recognized optional field, plus an unknown extension key, stays acceptable.
+  assert.equal(
+    resolveProtocolEra(
+      'tools/list',
+      withClientInfo({
+        ...valid,
+        title: 'Client',
+        description: 'A client',
+        websiteUrl: 'https://example.dev',
+        icons: [
+          {
+            src: 'https://example.dev/i.png',
+            mimeType: 'image/png',
+            sizes: ['48x48'],
+            theme: 'light',
+          },
+        ],
+        'com.example/extension': 1,
+      }),
+    ),
+    'modern',
+  );
+
+  for (const bad of [
+    42,
+    'client',
+    [],
+    { name: 'c' },
+    { version: '1' },
+    { ...valid, title: 42 },
+    { ...valid, description: 42 },
+    { ...valid, websiteUrl: 42 },
+    { ...valid, icons: 42 },
+    { ...valid, icons: [{}] },
+    { ...valid, icons: [{ src: 42 }] },
+    { ...valid, icons: [{ src: 'https://e.dev/i.png', mimeType: 42 }] },
+    { ...valid, icons: [{ src: 'https://e.dev/i.png', sizes: [48] }] },
+    { ...valid, icons: [{ src: 'https://e.dev/i.png', sizes: 'any' }] },
+    { ...valid, icons: [{ src: 'https://e.dev/i.png', theme: 'blue' }] },
+  ]) {
+    assert.throws(
+      () => resolveProtocolEra('tools/list', withClientInfo(bad)),
+      /clientInfo/,
+      `expected rejection for ${JSON.stringify(bad)}`,
+    );
+  }
+});
+
+test('the modern era removes initialize and ping, the legacy era keeps them', () => {
+  for (const method of ['initialize', 'ping']) {
+    assert.equal(isMethodRemovedInEra(method, 'modern'), true);
+    assert.equal(isMethodRemovedInEra(method, 'legacy'), false);
+  }
+  assert.equal(isMethodRemovedInEra('tools/call', 'modern'), false);
+});
+
+test('modern results carry resultType and serverInfo; legacy results are untouched', () => {
+  const modern = finalizeResult({ tools: [] }, 'modern') as Record<string, unknown>;
+  assert.equal(modern.resultType, 'complete');
+  assert.deepEqual(Object.keys((modern._meta ?? {}) as object), [
+    'io.modelcontextprotocol/serverInfo',
+  ]);
+
+  assert.deepEqual(finalizeResult({ tools: [] }, 'legacy'), { tools: [] });
+});
+
+test('finalizeResult preserves a result that already carries _meta', () => {
+  const result = finalizeResult({ tools: [], _meta: { 'com.example/trace': 'abc' } }, 'modern') as {
+    _meta: Record<string, unknown>;
+  };
+  assert.equal(result._meta['com.example/trace'], 'abc');
+  assert.ok(result._meta['io.modelcontextprotocol/serverInfo']);
+});
+
+test('cache hints ride modern results only', () => {
+  assert.deepEqual(cacheFields('modern', 1000), { ttlMs: 1000, cacheScope: 'public' });
+  assert.equal(cacheFields('legacy', 1000), undefined);
+});