chore: import upstream snapshot with attribution

tests/sandbox/test_pty_output.py

@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+import asyncio
+from collections import deque
+
+import pytest
+
+from agents.sandbox.session.pty_output import collect_pty_output
+
+
+@pytest.mark.asyncio
+async def test_collect_pty_output_waits_for_notification() -> None:
+    output_chunks: deque[bytes] = deque()
+    output_lock = asyncio.Lock()
+    output_notify = asyncio.Event()
+    done = False
+
+    async def produce_output() -> None:
+        nonlocal done
+        await asyncio.sleep(0)
+        async with output_lock:
+            output_chunks.append(b"notified output")
+        done = True
+        output_notify.set()
+
+    producer_task = asyncio.create_task(produce_output())
+    output, original_token_count = await collect_pty_output(
+        output_chunks=output_chunks,
+        output_lock=output_lock,
+        output_notify=output_notify,
+        is_done=lambda: done,
+        yield_time_ms=500,
+        max_output_tokens=None,
+    )
+    await producer_task
+
+    assert output == b"notified output"
+    assert original_token_count is None
+
+
+@pytest.mark.asyncio
+async def test_collect_pty_output_drains_chunks_added_when_done() -> None:
+    output_chunks = deque([b"before done"])
+
+    def mark_done() -> bool:
+        output_chunks.append(b" after done")
+        return True
+
+    output, original_token_count = await collect_pty_output(
+        output_chunks=output_chunks,
+        output_lock=asyncio.Lock(),
+        output_notify=asyncio.Event(),
+        is_done=mark_done,
+        yield_time_ms=500,
+        max_output_tokens=None,
+    )
+
+    assert output == b"before done after done"
+    assert original_token_count is None