Self-review of the settle path, which has been the source of every
regression in this branch. The server filters `turnId !== null &&
state === "running"` before settling; this filtered only on state.

No row is both null-id and running today — the sole null-id insert
writes 'pending' — so this changes no behavior. It is the invariant the
UPDATE already depends on, written down where it is relied upon, and it
keeps the two predicates directly comparable if a null-id running row
ever becomes possible.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>