Stop streaming commands cleanly on SIGTERM, like Ctrl-C

[alexkroman]

What

Make stream, agent, agent-cascade, and speak treat SIGTERM the same as Ctrl-C — a clean stop that flushes closing state and exits 0.

Why

The realtime commands already treat Ctrl-C (SIGINT → KeyboardInterrupt) as a graceful "user stopped" signal. But an external supervisor that stops the command from outside the terminal — a Hammerspoon hotkey, a service manager, a wrapper script's kill — sends SIGTERM, whose default action aborts the process before that flush runs. Delivering SIGINT instead is awkward: under a just/shell wrapper it means signalling the whole process group.

This came out of wiring assembly stream to a Hammerspoon start/stop hotkey: stopping cleanly required perl setpgrp + kill -INT -<pgid> gymnastics purely to deliver a clean SIGINT. With this change a controller just sends SIGTERM (e.g. Hammerspoon's hs.task:terminate()).

How

• New aai_cli/core/signals.py — terminate_as_interrupt() context manager: installs a SIGTERM handler that raises KeyboardInterrupt, so SIGTERM flows through each command's existing clean-stop path. Main-thread-only (no-op off-thread, where signal.signal is forbidden) and always restores the previous handler.
• Wrapped the interactive run of each streaming command with it: stream (single source + --from-stdin batch), agent, agent-cascade, speak.

No new flag; the behavior is transparent. SIGTERM mirrors whatever Ctrl-C already does per command (exit 0 for stream/agent/cascade; the same abort path for speak).

Tests

• tests/test_signals.py — handler install/restore + off-main-thread no-op.
• tests/test_stream_sigterm.py — both stream paths install the handler around the run.
• One wiring test each added to the agent, cascade, and speak suites. Each asserts the SIGTERM handler is the interrupt-raiser while the command runs, so removing a wrapper fails the test.

Full scripts/check.sh green locally (100% patch coverage, mutation gate passed).

🤖 Generated with Claude Code