Sibling site of the idle-resume rule from the stale-fold fix: the
assistant-tail append exit (user row persisted, no projection row) still
carried the journal's streamId onto a not-running resume, which kept the
journal entry alive (persistInFlightTurnState only clears when streamId is
null) and re-folded the same tail on every open. Apply the same
keepPending gate and pin it with a regression assertion.
Refs #85308
77248f8cb0