Greptile's two findings on the original PR were both right.
1. The scaler read test_durations.json from the checkout, but CI ran on
a fresh runner where that file never exists (it is gitignored and the
slicing-era artifact/merge job that produced it is gone). The feature
was inert exactly where the false FLAKY kills happen. tests.yml now
restores the most recent main-saved cache before the run (PRs read
only) and saves it after a green push to main, mirroring the
ci-timings-baseline restore/save pattern already in ci.yaml.
2. _save_durations persisted every file's total subprocess wall,
including the ~cap of a timed-out attempt and the retry-summed wall
of a FLAKY file. With the scaler that compounds: a hang cached at
~300s earns 900s next run, then ~900s cached earns 2700s, until the
job timeout is the only bound. _clean_pass_durations drops failed and
FLAKY files from the write so a file's cached duration is always a
first-attempt-clean measurement; those files keep their previous
known-good entry.
Tests trimmed to the salvage bar (<=2 invariants for the scaler plus one
for the cache filter) and moved next to the other runner tests under
tests/scripts/.
d228013832