🤖 fix: interrupt stream with pending bash tool near-instantly

[ammar-agent]

Problem

When InterruptStream (Ctrl+C) was called during a pending bash tool execution, the stream would hang indefinitely. This was especially problematic for SSH workspaces where long-running commands could block the UI for minutes.

Root Cause

The AI SDK's for await loop blocks waiting for the current async iterator operation to complete. When a bash tool is executing, the iterator doesn't yield until tool.execute() returns.

Even though we call abortController.abort(), the bash tool's abort listener was effectively empty:

abortListener = () => {
  if (!resolved) {
    // Runtime handles the actual cancellation  ← BUG: Does nothing!
    // We just need to clean up our side
  }
};

This caused:

1. cancelStreamSafely() calls abortController.abort()
2. Abort signal propagates but bash tool doesn't resolve
3. AI SDK iterator stays blocked waiting for tool to return
4. await streamInfo.processingPromise hangs indefinitely
5. IPC call never returns, UI frozen

For SSH workspaces, the SSH runtime's abort handler only kills the local SSH client - the remote command keeps running, making this worse.

Solution

Make the bash tool actively resolve its promise when aborted instead of passively waiting:

abortListener = () => {
  if (!resolved) {
    // Immediately resolve with abort error to unblock AI SDK stream
    teardown();
    resolveOnce({
      success: false,
      error: "Command execution was aborted",
      exitCode: -2,
      wall_duration_ms: Math.round(performance.now() - startTime),
    });
  }
};

This unblocks the chain:

• Tool promise resolves immediately with error
• AI SDK iterator yields
• Stream processing loop detects abort and exits
• processingPromise resolves
• IPC returns instantly

Testing

Added integration test that verifies interrupt completes in < 2 seconds even when a sleep 60 command is running:

test("should interrupt stream with pending bash tool call near-instantly", async () => {
  // Start sleep 60
  void sendMessage(workspaceId, "Run this bash command: sleep 60");
  await collector.waitForEvent("tool-call-start");
  
  // Measure interrupt time
  const start = performance.now();
  await interruptStream(workspaceId);
  const duration = performance.now() - start;
  
  expect(duration).toBeLessThan(2000); // Must be near-instant
});

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