feat: add resumeStream() method for clean SSE resumption API

Addresses PR feedback by providing a dedicated method for SSE stream
resumption instead of using send() with a fake notification.

Author: felixweinberger

src/client/streamableHttp.ts

@@ -620,4 +620,18 @@ export class StreamableHTTPClientTransport implements Transport {
     get protocolVersion(): string | undefined {
         return this._protocolVersion;
     }
+
+    /**
+     * Resume an SSE stream from a previous event ID.
+     * Opens a GET SSE connection with Last-Event-ID header to replay missed events.
+     *
+     * @param lastEventId The event ID to resume from
+     * @param options Optional callback to receive new resumption tokens
+     */
+    async resumeStream(lastEventId: string, options?: { onresumptiontoken?: (token: string) => void }): Promise<void> {
+        await this._startOrAuthSse({
+            resumptionToken: lastEventId,
+            onresumptiontoken: options?.onresumptiontoken
+        });
+    }
 }

src/integration-tests/taskResumability.test.ts

@@ -251,13 +251,8 @@ describe.each(zodTestMatrix)('$zodVersionLabel', (entry: ZodMatrixEntry) => {
             await client2.connect(transport2);
 
             // Resume GET SSE stream with Last-Event-ID to replay missed events
-            // Per spec, resumption uses GET with Last-Event-ID header, not POST
-            // When resumptionToken is provided, send() only triggers GET reconnection and returns early
-            // We use a notification (no id) so we don't expect a response
-            await transport2.send(
-                { jsonrpc: '2.0', method: 'notifications/ping' },
-                { resumptionToken: lastEventId, onresumptiontoken: onLastEventIdUpdate }
-            );
+            // Per spec, resumption uses GET with Last-Event-ID header
+            await transport2.resumeStream(lastEventId!, { onresumptiontoken: onLastEventIdUpdate });
 
             // Wait for replayed events to arrive via SSE
             await new Promise(resolve => setTimeout(resolve, 100));