Implement MCP 2026-07-28 (#2286)

Co-authored-by: Matt <77928207+mattzcarey@users.noreply.github.com>
Co-authored-by: Konstantin Konstantinov <KKonstantinov@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

examples/json-response/client.ts

@@ -0,0 +1,49 @@
+/**
+ * Asserts the `responseMode: 'json'` server answers a `tools/call` with a
+ * `Content-Type: application/json` body (not `text/event-stream`) AND that the
+ * regular `Client` works against it unchanged.
+ *
+ * HTTP-only, modern-only — `responseMode` shapes the 2026-07-28 per-request
+ * HTTP path; there is no stdio equivalent and 2025-era traffic goes through
+ * the stateless legacy fallback unaffected.
+ */
+import { check, parseExampleArgs } from '@mcp-examples/shared';
+import { Client, StreamableHTTPClientTransport } from '@modelcontextprotocol/client';
+
+const { url } = parseExampleArgs();
+
+const client = new Client({ name: 'json-response-example-client', version: '1.0.0' }, { versionNegotiation: { mode: 'auto' } });
+
+await client.connect(new StreamableHTTPClientTransport(new URL(url)));
+
+// Low-level: a 2026-07-28 (envelope) request should come back as plain JSON —
+// the JSON content-type assertion is the point of the story.
+const probe = await fetch(url, {
+    method: 'POST',
+    headers: {
+        'content-type': 'application/json',
+        accept: 'application/json, text/event-stream',
+        'mcp-protocol-version': '2026-07-28',
+        'mcp-method': 'tools/list'
+    },
+    body: JSON.stringify({
+        jsonrpc: '2.0',
+        id: 1,
+        method: 'tools/list',
+        params: {
+            _meta: {
+                'io.modelcontextprotocol/protocolVersion': '2026-07-28',
+                'io.modelcontextprotocol/clientInfo': { name: 'probe', version: '1.0.0' },
+                'io.modelcontextprotocol/clientCapabilities': {}
+            }
+        }
+    })
+});
+check.match(probe.headers.get('content-type') ?? '', /application\/json/);
+check.equal(probe.status, 200);
+
+// High-level: the regular Client works unchanged.
+const result = await client.callTool({ name: 'greet', arguments: { name: 'json' } });
+check.equal(result.content?.[0]?.type === 'text' ? result.content[0].text : '', 'Hello, json!');
+
+await client.close();