fix(a2a-server): delimit SSE events with a blank line in /executeCommand

The streaming `/executeCommand` handler wrote each Server-Sent Event with a
single trailing newline (`data: <json>\n`). The SSE specification requires
events to be separated by a blank line (`\n\n`); without it a spec-compliant
EventSource client coalesces every event into one record and never dispatches a
well-formed event, so streaming command output is unusable for real clients.

The existing streaming test did not catch this because it used the Mocha-style
`done` callback, which Vitest 3 does not honour: the test body returned before
its assertions ran, so the test always passed regardless of the payload. Convert
that test to async/await so it actually verifies the emitted events. It fails
before this fix (1 event parsed instead of 2) and passes after.

Author: Pluviobyte

packages/a2a-server/src/http/app.test.ts

@@ -1134,9 +1134,7 @@ describe('E2E Tests', () => {
     });
 
     describe('/executeCommand streaming', () => {
-      it('should execute a streaming command and stream back events', (done: (
-        err?: unknown,
-      ) => void) => {
+      it('should execute a streaming command and stream back events', async () => {
         const executeSpy = vi.fn(async (context: CommandContext) => {
           context.eventBus?.publish({
             kind: 'status-update',
@@ -1164,42 +1162,30 @@ describe('E2E Tests', () => {
         vi.spyOn(commandRegistry, 'get').mockReturnValue(mockStreamCommand);
 
         const agent = request.agent(app);
-        agent
+        const res = await agent
           .post('/executeCommand')
           .send({ command: 'stream-test', args: [] })
           .set('Content-Type', 'application/json')
           .set('Accept', 'text/event-stream')
-          .on('response', (res) => {
-            let data = '';
-            res.on('data', (chunk: Buffer) => {
-              data += chunk.toString();
-            });
-            res.on('end', () => {
-              try {
-                const events = streamToSSEEvents(data);
-                expect(events.length).toBe(2);
-                expect(events[0].result).toEqual({
-                  kind: 'status-update',
-                  status: { state: 'working' },
-                  taskId: 'test-task',
-                  contextId: 'test-context',
-                  final: false,
-                });
-                expect(events[1].result).toEqual({
-                  kind: 'status-update',
-                  status: { state: 'completed' },
-                  taskId: 'test-task',
-                  contextId: 'test-context',
-                  final: true,
-                });
-                expect(executeSpy).toHaveBeenCalled();
-                done();
-              } catch (e) {
-                done(e);
-              }
-            });
-          })
-          .end();
+          .expect(200);
+
+        const events = streamToSSEEvents(res.text);
+        expect(events.length).toBe(2);
+        expect(events[0].result).toEqual({
+          kind: 'status-update',
+          status: { state: 'working' },
+          taskId: 'test-task',
+          contextId: 'test-context',
+          final: false,
+        });
+        expect(events[1].result).toEqual({
+          kind: 'status-update',
+          status: { state: 'completed' },
+          taskId: 'test-task',
+          contextId: 'test-context',
+          final: true,
+        });
+        expect(executeSpy).toHaveBeenCalled();
       });
 
       it('should handle non-streaming commands gracefully', async () => {

packages/a2a-server/src/http/app.ts

@@ -167,7 +167,7 @@ async function handleExecuteCommand(
           id: 'taskId' in event ? event.taskId : (event as Message).messageId,
           result: event,
         };
-        res.write(`data: ${JSON.stringify(jsonRpcResponse)}\n`);
+        res.write(`data: ${JSON.stringify(jsonRpcResponse)}\n\n`);
       };
       eventBus.on('event', eventHandler);