The sticky refresh path and reservation reconciliation both took the fleet-wide
`relay_cells ... FOR UPDATE` scan to mutate one or two rows, so one busy cell
queued unrelated reconnects and migration completions behind it. Both now lock
only the rows they touch, in the same ascending cell_id order, and the sticky
grant moves its counter by a delta instead of writing back a snapshot value.
Placement keeps the ordered inventory lock: choosing the least-loaded cell is a
genuinely fleet-wide decision, and dynamically locking only the selected target
is what allowed cross-cell cycles before.
The pool's statement_timeout becomes env-configurable and a 57014 now reaches
the bounded transaction retry instead of surfacing as a terminal failure.
Schema DDL moves to its own `max: 1`, statement_timeout-free pool that is ended
before the serving pool opens, so a slow CREATE INDEX cannot inherit a request
deadline it will never fit inside.
