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/sse-polling/client.ts

@@ -0,0 +1,48 @@
+/**
+ * SSE Polling Example Client (SEP-1699)
+ *
+ * Connects (2025-era), calls `long-operation`, and asserts the result arrives
+ * AFTER the server's mid-stream `closeSSE()` — i.e. the client transport
+ * automatically reconnects with `Last-Event-ID` and replays the events the
+ * `eventStore` buffered while disconnected. Also asserts every progress log
+ * (including the one emitted while disconnected) was delivered.
+ */
+import { check, parseExampleArgs } from '@mcp-examples/shared';
+import { Client, StreamableHTTPClientTransport } from '@modelcontextprotocol/client';
+
+const { url } = parseExampleArgs();
+
+// `closeSSE`/`eventStore` live on the sessionful-2025 transport, so this
+// story is legacy-only by design — it was previously reaching 2025 by
+// negotiation fallback; pin it.
+const client = new Client({ name: 'sse-polling-client', version: '1.0.0' }, { versionNegotiation: { mode: 'legacy' } });
+const logs: string[] = [];
+client.setNotificationHandler('notifications/message', n => {
+    logs.push(String(n.params.data));
+});
+
+const transport = new StreamableHTTPClientTransport(new URL(url));
+// The mid-stream disconnect surfaces as a transport error before the
+// automatic reconnect; that is the EXPECTED flow, not a failure.
+transport.onerror = () => {};
+await client.connect(transport);
+
+let lastEventId: string | undefined;
+const result = await client.request(
+    { method: 'tools/call', params: { name: 'long-operation', arguments: {} } },
+    { onresumptiontoken: token => (lastEventId = token) }
+);
+
+const text = (result as { content?: Array<{ type: string; text?: string }> }).content?.[0]?.text ?? '';
+check.match(text, /completed successfully/);
+check.ok(lastEventId, 'resumption tokens should have been observed');
+// The 75% line is emitted WHILE the client is disconnected; receiving it
+// proves the event store replayed it on reconnect. (Replay ordering relative
+// to the terminal result is not asserted — the result resolving is the
+// signal the disconnect was survived.)
+check.ok(
+    logs.some(l => l.includes('75%')),
+    `events emitted while disconnected should be replayed (got: ${logs.join(' | ')})`
+);
+
+await client.close();