fix(ai-client): capture abort signal before await to prevent race condition

packages/typescript/ai-client/src/chat-client.ts

@@ -430,6 +430,10 @@ export class ChatClient {
     this.setStatus('submitted')
     this.setError(undefined)
     this.abortController = new AbortController()
+    // Capture the signal immediately so that a concurrent stop() or
+    // sendMessage() that reassigns this.abortController cannot cause
+    // connect() to receive a stale or null signal.
+    const signal = this.abortController.signal
     // Reset pending tool executions for the new stream
     this.pendingToolExecutions.clear()
     let streamCompletedSuccessfully = false
@@ -456,7 +460,7 @@ export class ChatClient {
       const stream = this.connection.connect(
         messages,
         mergedBody,
-        this.abortController.signal,
+        signal,
       )
 
       await this.processStream(stream)

packages/typescript/ai-client/tests/chat-client-abort.test.ts

@@ -306,4 +306,101 @@ describe('ChatClient - Abort Signal Handling', () => {
     // Each should be a different signal instance
     expect(abortSignals[0]).not.toBe(abortSignals[1])
   })
+
+  it('should pass the original signal to connect() even if stop() is called during onResponse', async () => {
+    let signalPassedToConnect: AbortSignal | undefined
+
+    const adapter: ConnectionAdapter = {
+      // eslint-disable-next-line @typescript-eslint/require-await
+      async *connect(_messages, _data, abortSignal) {
+        signalPassedToConnect = abortSignal
+        yield {
+          type: 'RUN_FINISHED',
+          runId: 'run-1',
+          model: 'test',
+          timestamp: Date.now(),
+          finishReason: 'stop',
+        }
+      },
+    }
+
+    const client = new ChatClient({
+      connection: adapter,
+      onResponse: () => {
+        // Simulate a concurrent stop() during the onResponse callback,
+        // which sets this.abortController to null. Without the fix,
+        // the code would dereference this.abortController.signal after
+        // this point and crash with a null reference.
+        client.stop()
+      },
+    })
+
+    await client.append({
+      id: 'user-1',
+      role: 'user',
+      parts: [{ type: 'text', content: 'Hello' }],
+      createdAt: new Date(),
+    })
+
+    // The signal should still be a valid AbortSignal instance
+    // (captured before the await), not undefined/null
+    expect(signalPassedToConnect).toBeInstanceOf(AbortSignal)
+  })
+
+  it('should pass the original signal to connect() even if sendMessage() reassigns abortController during onResponse', async () => {
+    const signalsPassedToConnect: Array<AbortSignal> = []
+    let secondAppendPromise: Promise<unknown> | undefined
+
+    const adapter: ConnectionAdapter = {
+      // eslint-disable-next-line @typescript-eslint/require-await
+      async *connect(_messages, _data, abortSignal) {
+        if (abortSignal) {
+          signalsPassedToConnect.push(abortSignal)
+        }
+        yield {
+          type: 'RUN_FINISHED',
+          runId: 'run-1',
+          model: 'test',
+          timestamp: Date.now(),
+          finishReason: 'stop',
+        }
+      },
+    }
+
+    let firstCall = true
+    const client = new ChatClient({
+      connection: adapter,
+      onResponse: () => {
+        if (firstCall) {
+          firstCall = false
+          // Trigger a second message during onResponse callback.
+          // This queues a new streamResponse that would create a new
+          // AbortController, potentially overwriting this.abortController
+          // before the first connect() call reads the signal.
+          secondAppendPromise = client.append({
+            id: 'user-2',
+            role: 'user',
+            parts: [{ type: 'text', content: 'Second message' }],
+            createdAt: new Date(),
+          })
+        }
+      },
+    })
+
+    await client.append({
+      id: 'user-1',
+      role: 'user',
+      parts: [{ type: 'text', content: 'Hello' }],
+      createdAt: new Date(),
+    })
+
+    // Deterministically wait for the queued second stream
+    await secondAppendPromise
+
+    // Both calls should have received valid, distinct AbortSignal instances
+    expect(signalsPassedToConnect.length).toBe(2)
+    expect(signalsPassedToConnect[0]).toBeInstanceOf(AbortSignal)
+    expect(signalsPassedToConnect[1]).toBeInstanceOf(AbortSignal)
+    expect(signalsPassedToConnect[0]).not.toBe(signalsPassedToConnect[1])
+  })
 })