The five internal/app partitions ran end to end inside one job, so the app
shard's wall clock was the sum of all five: 780s in CI, of which the schema
partition owned 357s. Each partition is now its own matrix shard, so they run
concurrently and the shard's wall clock is set by its slowest partition rather
than by their total. Every partition shard still selects the same single
internal/app package, so the impacted-package query maps the shard name back to
app and the partition only chooses which tests run.
The helper gains a partition argument and a list-partitions mode. APP_PARTITIONS
is the single source of truth for the set, and the discovery pass still runs in
every job, so each one independently verifies that the partition patterns cover
every top-level test exactly once before running the one it was asked for.
Two fail-closed checks guard the split, because the helper's own coverage check
can no longer prove the whole package ran once the partitions are separate jobs:
- The helper cross-checks APP_PARTITIONS against the coverage counters in both
directions, so a counted partition that nothing dispatches and a dispatchable
partition with no counter both fail instead of silently skipping tests.
- TestCIAppRacePartitionMatrixMatchesHelper pins the workflow's app-<partition>
shards to list-partitions output in both directions, so a partition cannot
lose its job while every job stays green.
The discovery loop variable is renamed from partition to spec: it would
otherwise shadow the partition requested on the command line, which run mode
reads after the discovery pass completes.
chichuan
bfd0976b31