The startup JS gzip gate was a fixed ceiling that main drifted to within
1-3 KiB of, forcing repeated hand-bumps (315->317 KiB) and failing
feature PRs on drift they did not cause (#112649 burned two CI rounds).
check-control-ui-performance.mjs now also enforces a committed baseline
(config/control-ui-startup-budget-baseline.json) with a 512 B tolerance:
regressions beyond baseline+tolerance fail with an actionable message,
intentional increases become a reviewed one-line diff via
--update-baseline --reason, meaningfully lighter builds print a
lower-the-baseline hint, and a malformed/missing baseline fails closed.
The fixed ceiling stays as the cumulative-creep backstop.
Closes#112743.
