fix(streaming): clear output callback on cancellation

[chaliy]

Motivation

• Prevent stale interpreter output callbacks from surviving if a streaming execution future is cancelled or dropped, which can leak stdout/stderr into later executions and cross-request contexts.

Description

• Introduce an RAII guard OutputCallbackGuard that installs the callback via install and clears it in Drop to make cleanup cancellation-safe and robust across await points. (crates/bashkit/src/lib.rs)
• Mark the guard Send with a safety comment so it can travel across executor boundaries while still ensuring unique access to the interpreter. (crates/bashkit/src/lib.rs)
• Use the guard in exec_streaming_with_extensions so callbacks are cleared even if the streaming future is cancelled. (crates/bashkit/src/lib.rs)
• Add a Rust regression test test_exec_streaming_cancel_clears_callback proving a timed-out/cancelled streaming run does not receive later output. (crates/bashkit/src/lib.rs)
• Add a Python async regression test_execute_on_output_cancel_does_not_poison_future_calls covering asyncio.wait_for cancellation for both Bash and BashTool. (crates/bashkit-python/tests/test_streaming_output.py)

Testing

• cargo test -p bashkit test_exec_streaming_cancel_clears_callback --lib — passed.
• VIRTUAL_ENV=$PWD/.uv-venv-bashkit PATH=$PWD/.uv-venv-bashkit/bin:$PATH uvx maturin develop --manifest-path crates/bashkit-python/Cargo.toml and python -m pytest crates/bashkit-python/tests/test_streaming_output.py -q — Python tests passed (26 passed).
• cargo clippy -p bashkit --lib -- -D warnings — passed.
• cargo fmt --check and ruff check / ruff format --check on the modified Python test file — passed.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	bashkit	2f2d295	Commit Preview URL	Jun 02 2026, 09:36 AM