The third bug is the one worth dwelling on. Dropping thinking blocks every turn instead of just once is the kind of regression that only shows up in production traffic. A unit test for "idle-threshold clearing" would assert "was thinking cleared after an hour of idle" (yes) without asserting "is thinking preserved on subsequent turns" (no). The invariant is negative space.
The real lesson is that an internal message-queuing experiment masked the symptoms in their own dogfooding. Dogfooding only works when the eaten food is the shipped food.
Experienced engineers that know the codebase and system well, and with enough time to consider the problem properly would likely consider this case.
But if we're vibing... This is the kind of bug that should make it back into a review agent/skill's instructions in a more generic format. Essentially if something is done to the message history, check there tests that subsequent turns work as expected.
But yeah, you'd have to piss off a bunch of users in prod first to discover the blind spot.