Align 2026-07-28 wire with spec PR #3002: serverInfo in result _meta, clientInfo optional (#2513)

packages/client/test/client/connectPrior.test.ts

@@ -48,7 +48,7 @@ class ScriptedTransport implements Transport {
 const discoverResult = (supportedVersions: string[]): DiscoverResult => ({
     supportedVersions,
     capabilities: { tools: { listChanged: true } },
-    serverInfo: { name: 'persisted-server', version: '1.0.0' },
+    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'persisted-server', version: '1.0.0' } },
     instructions: 'persisted instructions'
 });
 
@@ -149,7 +149,7 @@ describe('getDiscoverResult() round-trip', () => {
                     result: {
                         supportedVersions: [MODERN],
                         capabilities: { tools: {} },
-                        serverInfo: { name: 'probed-server', version: '2.0.0' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'probed-server', version: '2.0.0' } }
                     }
                 });
             }
@@ -157,7 +157,7 @@ describe('getDiscoverResult() round-trip', () => {
         const bootstrap = new Client({ name: 'bootstrap', version: '0' }, { versionNegotiation: { mode: 'auto' } });
         await bootstrap.connect(bootstrapTransport);
         const probed = bootstrap.getDiscoverResult();
-        expect(probed?.serverInfo).toEqual({ name: 'probed-server', version: '2.0.0' });
+        expect(bootstrap.getServerVersion()).toEqual({ name: 'probed-server', version: '2.0.0' });
         expect(probed?.supportedVersions).toEqual([MODERN]);
         await bootstrap.close();
         // close() clears per-connection state.
@@ -190,17 +190,19 @@ describe('getDiscoverResult() round-trip', () => {
                         cacheScope: 'public',
                         supportedVersions: [MODERN],
                         capabilities: { tools: {} },
-                        serverInfo: { name: 'rediscovered', version: '3.0.0' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'rediscovered', version: '3.0.0' } }
                     }
                 });
             }
         });
         const client = new Client({ name: 'c', version: '0' });
         await client.connect(transport, { prior: modernPrior([MODERN]) });
-        expect(client.getDiscoverResult()?.serverInfo.name).toBe('persisted-server');
+        const metaName = (r?: { _meta?: Record<string, unknown> }) =>
+            (r?._meta?.['io.modelcontextprotocol/serverInfo'] as { name?: string } | undefined)?.name;
+        expect(metaName(client.getDiscoverResult())).toBe('persisted-server');
         const fresh = await client.discover();
-        expect(fresh.serverInfo.name).toBe('rediscovered');
-        expect(client.getDiscoverResult()?.serverInfo.name).toBe('rediscovered');
+        expect(metaName(fresh)).toBe('rediscovered');
+        expect(metaName(client.getDiscoverResult())).toBe('rediscovered');
         await client.close();
     });
 });
@@ -348,4 +350,24 @@ describe('connect({ prior }) — malformed persisted blobs (runtime hardening)',
         );
         expect(transport.sent).toHaveLength(0);
     });
+
+    test('a stale blob with a body serverInfo (not a spec field) connects with anonymous identity — the body is never read', async () => {
+        // The 2026-07-28 revision has no body serverInfo on DiscoverResult:
+        // identity travels in _meta (spec PR #3002). A persisted blob carrying
+        // the non-spec body member is still a schema-valid DiscoverResult
+        // (loose results tolerate unknown members), so validatePrior accepts
+        // it — but the identity read consults _meta only, so the connection is
+        // anonymous rather than adopting a field the spec does not define.
+        const transport = new ScriptedTransport();
+        const client = new Client({ name: 'worker', version: '0' });
+
+        const blob =
+            '{"kind":"modern","discover":{"supportedVersions":["2026-07-28"],"capabilities":{},' +
+            '"serverInfo":{"name":"stale-server","version":"0.4.0"}}}';
+        await client.connect(transport, { prior: JSON.parse(blob) as PriorDiscovery });
+        expect(transport.sent).toHaveLength(0);
+        expect(client.getProtocolEra()).toBe('modern');
+        expect(client.getServerVersion()).toBeUndefined();
+        await client.close();
+    });
 });

packages/client/test/client/discover.test.ts

@@ -44,7 +44,7 @@ const discoverBody = {
     cacheScope: 'public',
     supportedVersions: [MODERN],
     capabilities: { tools: {} },
-    serverInfo: { name: 'modern-server', version: '1.0.0' },
+    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'modern-server', version: '1.0.0' } },
     instructions: 'modern instructions'
 };
 
@@ -78,7 +78,7 @@ describe('Client.discover()', () => {
 
         const advertisement = await client.discover();
         expect(advertisement.supportedVersions).toEqual([MODERN]);
-        expect(advertisement.serverInfo).toEqual({ name: 'modern-server', version: '1.0.0' });
+        expect(advertisement._meta?.['io.modelcontextprotocol/serverInfo']).toEqual({ name: 'modern-server', version: '1.0.0' });
         expect(advertisement.instructions).toBe('modern instructions');
 
         await client.close();
@@ -99,3 +99,49 @@ describe('Client.discover()', () => {
         await client.close();
     });
 });
+
+describe('server identity from a DiscoverResult (#3002: _meta only)', () => {
+    const base = { resultType: 'complete', ttlMs: 0, cacheScope: 'public', supportedVersions: [MODERN], capabilities: {} };
+    const metaIdentity = { name: 'meta-server', version: '2.0.0' };
+
+    async function connectAgainst(result: Record<string, unknown>): Promise<Client> {
+        const transport = new ScriptedTransport((message, t) => {
+            if (isJSONRPCRequest(message) && message.method === 'server/discover') {
+                t.reply({ jsonrpc: '2.0', id: message.id, result });
+            }
+        });
+        const client = new Client({ name: 'c', version: '0' }, { versionNegotiation: { mode: { pin: MODERN } } });
+        await client.connect(transport);
+        return client;
+    }
+
+    test('serverInfo in _meta yields the identity', async () => {
+        const client = await connectAgainst({ ...base, _meta: { 'io.modelcontextprotocol/serverInfo': metaIdentity } });
+        expect(client.getServerVersion()).toEqual(metaIdentity);
+        await client.close();
+    });
+
+    test('a stray body serverInfo is ignored — identity comes from _meta only', async () => {
+        const client = await connectAgainst({ ...base, serverInfo: { name: 'body-only', version: '0.9.0' } });
+        expect(client.getServerVersion()).toBeUndefined();
+        await client.close();
+    });
+
+    test('absent identity → undefined, connection still established (serverInfo is a SHOULD)', async () => {
+        const client = await connectAgainst(base);
+        expect(client.getServerVersion()).toBeUndefined();
+        await client.close();
+    });
+
+    test('a MALFORMED _meta serverInfo still connects modern through the real transport path (regression: the neutral-schema classification guard must not drop the frame)', async () => {
+        // Exercises the full inbound pipeline — transport.onmessage →
+        // isJSONRPCResultResponse (neutral JSONRPCResultResponseSchema) →
+        // probe classification — not a pre-built ProbeOutcome. A strict
+        // neutral serverInfo key made this connect fail before the frame
+        // reached the lenient wire schema.
+        const client = await connectAgainst({ ...base, _meta: { 'io.modelcontextprotocol/serverInfo': 'utterly-bogus' } });
+        expect(client.getNegotiatedProtocolVersion()).toBe(MODERN);
+        expect(client.getServerVersion()).toBeUndefined();
+        await client.close();
+    });
+});

packages/client/test/client/envelopeAutoEmission.test.ts

@@ -47,7 +47,7 @@ async function scriptedServerSide(era: 'modern' | 'legacy', answerToolsList = tr
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: { tools: {} },
-                        serverInfo: { name: 'scripted-modern-server', version: '1.0.0' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted-modern-server', version: '1.0.0' } }
                     }
                 });
             } else {

packages/client/test/client/inputRequiredEngine.test.ts

@@ -45,7 +45,7 @@ async function scriptedModernServer(respondToToolCall: (request: JSONRPCRequest,
                     resultType: 'complete',
                     supportedVersions: [MODERN],
                     capabilities: { tools: {} },
-                    serverInfo: { name: 'scripted-mrtr-server', version: '1.0.0' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted-mrtr-server', version: '1.0.0' } }
                 }
             });
             return;

packages/client/test/client/listen.test.ts

@@ -36,7 +36,7 @@ async function scriptedModern(onListen?: (id: number | string, filter: unknown,
                     resultType: 'complete',
                     supportedVersions: [MODERN],
                     capabilities: { tools: { listChanged: true }, prompts: { listChanged: true } },
-                    serverInfo: { name: 'scripted', version: '1' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted', version: '1' } }
                 }
             });
         }
@@ -73,7 +73,7 @@ async function scriptedModernNoAck() {
                     resultType: 'complete',
                     supportedVersions: [MODERN],
                     capabilities: { tools: { listChanged: true }, prompts: { listChanged: true } },
-                    serverInfo: { name: 'scripted', version: '1' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted', version: '1' } }
                 }
             });
         }
@@ -249,7 +249,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: {},
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }
@@ -278,7 +278,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: {},
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }
@@ -340,7 +340,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: {},
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }
@@ -419,7 +419,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: {},
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }
@@ -554,7 +554,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: { tools: { listChanged: true } },
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }
@@ -679,7 +679,7 @@ describe('Client.listen()', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: { tools: { listChanged: true } },
-                        serverInfo: { name: 's', version: '1' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1' } }
                     }
                 });
             }

packages/client/test/client/mcpParamMirroring.test.ts

@@ -72,7 +72,7 @@ async function scriptedModernServer(pages: Tool[][], rejectFirstCall = false): P
                     resultType: 'complete',
                     supportedVersions: [MODERN],
                     capabilities: { tools: { listChanged: true } },
-                    serverInfo: { name: 'scripted', version: '1.0.0' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted', version: '1.0.0' } }
                 }
             });
         } else if (r.method === 'tools/list') {

packages/client/test/client/modernEraInboundDrop.test.ts

@@ -36,7 +36,7 @@ async function scriptedServerSide(eras: 'modern' | 'legacy') {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: { tools: {} },
-                        serverInfo: { name: 'scripted-modern-server', version: '1.0.0' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted-modern-server', version: '1.0.0' } }
                     }
                 });
             } else {

packages/client/test/client/probeClassifier.test.ts

@@ -31,7 +31,7 @@ function classify(outcome: ProbeOutcome, context: Partial<ProbeClassifierContext
 const discoverResult = (supportedVersions: string[]) => ({
     supportedVersions,
     capabilities: { tools: {} },
-    serverInfo: { name: 'fixture-server', version: '1.0.0' }
+    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'fixture-server', version: '1.0.0' } }
 });
 
 /** The deployed-fleet 400 body for a JSON-RPC error (server streamableHttp `createJsonErrorResponse`). */
@@ -57,7 +57,7 @@ describe('row: DiscoverResult with version overlap → modern, select from suppo
         expect(verdict.kind).toBe('modern');
         if (verdict.kind === 'modern') {
             expect(verdict.discover.capabilities).toEqual({ tools: {} });
-            expect(verdict.discover.serverInfo.name).toBe('fixture-server');
+            expect(verdict.discover._meta?.['io.modelcontextprotocol/serverInfo']).toEqual({ name: 'fixture-server', version: '1.0.0' });
         }
     });
 });

packages/client/test/client/probeFixtureCorpus.test.ts

@@ -53,6 +53,20 @@ const DEPLOYED_SESSION_REQUIRED_BODY = JSON.stringify({
     error: { code: -32_000, message: 'Bad Request: Server not initialized' }
 });
 
+/**
+ * The exact discover result a go-sdk v1.7.0-pre.3 server answers the probe
+ * with (spec PR #3002 final 2026-07-28 shape): `serverInfo` lives in the
+ * result `_meta`, the body field is gone.
+ */
+const GO_V17_DISCOVER_RESULT = {
+    resultType: 'complete',
+    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'server', version: 'v0.0.1' } },
+    ttlMs: 0,
+    cacheScope: 'public',
+    supportedVersions: ['2026-07-28', '2025-11-25', '2025-06-18', '2025-03-26', '2024-11-05'],
+    capabilities: { logging: {} }
+};
+
 interface CorpusRow {
     name: string;
     outcome: ProbeOutcome;
@@ -78,7 +92,7 @@ const CORPUS: CorpusRow[] = [
         name: 'T9: DiscoverResult with no mutual version + fallback available → legacy (initialize on the same connection)',
         outcome: {
             kind: 'result',
-            result: { supportedVersions: ['2027-01-01'], capabilities: {}, serverInfo: { name: 's', version: '1' } }
+            result: { supportedVersions: ['2027-01-01'], capabilities: {} }
         },
         expected: 'legacy'
     },
@@ -86,7 +100,7 @@ const CORPUS: CorpusRow[] = [
         name: 'T9: DiscoverResult with no mutual version + NO fallback (pin / modern-only) → typed error, never initialize',
         outcome: {
             kind: 'result',
-            result: { supportedVersions: ['2027-01-01'], capabilities: {}, serverInfo: { name: 's', version: '1' } }
+            result: { supportedVersions: ['2027-01-01'], capabilities: {} }
         },
         context: { fallbackAvailable: false },
         expected: 'error'
@@ -164,6 +178,26 @@ const CORPUS: CorpusRow[] = [
         name: 'wire-real: -32601 method-not-found → legacy fallback',
         outcome: { kind: 'rpc-error', code: -32_601, message: 'Method not found' },
         expected: 'legacy'
+    },
+    // --- Wire-real shape C: the #3002 final-revision DiscoverResult (go v1.7.0-pre.3).
+    // Regression: before the #3002 alignment the wire schema required body
+    // `serverInfo`, so this conforming response failed parse and misclassified
+    // legacy — the client then attempted `initialize` against a modern server.
+    {
+        name: 'wire-real: go v1.7.0-pre.3 DiscoverResult (#3002 shape, serverInfo in _meta) → modern',
+        outcome: { kind: 'result', result: GO_V17_DISCOVER_RESULT },
+        expected: 'modern'
+    },
+    // A malformed _meta serverInfo is display-only material and must not
+    // demote a conforming DiscoverResult to legacy (receiver leniency: the
+    // wire schema drops the bad value instead of failing the parse).
+    {
+        name: 'recognizer: DiscoverResult with a malformed _meta serverInfo → still modern',
+        outcome: {
+            kind: 'result',
+            result: { ...GO_V17_DISCOVER_RESULT, _meta: { 'io.modelcontextprotocol/serverInfo': 'bogus' } }
+        },
+        expected: 'modern'
     }
 ];
 
@@ -179,7 +213,7 @@ describe('T9/T11 merged probe fixture corpus (probe classifier)', () => {
         const verdict = classifyProbeOutcome(
             {
                 kind: 'result',
-                result: { supportedVersions: [MODERN], capabilities: {}, serverInfo: { name: 's', version: '1' } }
+                result: { supportedVersions: [MODERN], capabilities: {} }
             },
             baseContext
         );

packages/client/test/client/responseCache.test.ts

@@ -345,7 +345,7 @@ async function scriptedModernServer(pages: Tool[][], opts: ScriptOptions = {}):
                     resultType: 'complete',
                     supportedVersions: [MODERN],
                     capabilities: { tools: { listChanged: true }, prompts: {}, resources: {} },
-                    serverInfo: opts.serverInfo ?? { name: 'scripted', version: '1.0.0' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': opts.serverInfo ?? { name: 'scripted', version: '1.0.0' } }
                 }
             });
         } else if (r.method === 'tools/list') {
@@ -1210,7 +1210,7 @@ describe('Client honours cacheHints (SEP-2549)', () => {
                         resultType: 'complete',
                         supportedVersions: [MODERN],
                         capabilities: { resources: {} },
-                        serverInfo: { name: 'scripted', version: '1.0.0' }
+                        _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted', version: '1.0.0' } }
                     }
                 });
             } else if (r.method === 'resources/read') {

packages/client/test/client/responseCacheCodec.test.ts

@@ -27,7 +27,7 @@ async function connectedPair() {
                     resultType: 'complete',
                     supportedVersions: ['2026-07-28'],
                     capabilities: { tools: {} },
-                    serverInfo: { name: 's', version: '1.0.0' }
+                    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 's', version: '1.0.0' } }
                 }
             });
         } else if (r.method === 'tools/list') {

packages/client/test/client/versionNegotiation.test.ts

@@ -118,7 +118,7 @@ class ScriptedTransport implements Transport {
 const discoverResult = (supportedVersions: string[]) => ({
     supportedVersions,
     capabilities: {},
-    serverInfo: { name: 'scripted-modern-server', version: '1.0.0' }
+    _meta: { 'io.modelcontextprotocol/serverInfo': { name: 'scripted-modern-server', version: '1.0.0' } }
 });
 
 /** A scripted dual-era server: answers server/discover with a DiscoverResult and initialize like a 2025 server. */