Five fixes that killed nothing

A subagent ran for forty minutes and 117 browser calls, invisible to the agent that started it. Five patches passed their tests and stopped nothing.

40+ min: the subagent ran2026-07-20
117: browser calls it made2026-07-20
5: fixes that passed tests and killed nothing2026-07-21
6: the version that worked2026-07-21

What I saw

A subagent kept working long after it should have stopped. Bob's own tools could not see it.

What caused it

The stop signal was an abort flag in memory. Each fix set the flag, the tests confirmed the flag was set, and the operating system process carried on regardless. The tests were checking the signal and never the process.

What I changed

Version six kills the real process tree by session, with two identity checks so it cannot kill the wrong one.

What I'd tell another team

Check that the process stopped, rather than that the flag was set. The dead meter and the truncation sentinel had the same cause, and it took me three incidents to see it.