- ci.yml runs test (plain|san, 1..3/3) on macos-15; an aggregate job keeps the old "test" check name for anything pinned to it
- each job runs vitest twice: --shard=i/3 over everything but the corpus lanes, then the four corpus lanes with only their case slice — a file lands in exactly one --shard slice, so mixing the axes would silently drop cases
- tests/harness/shard.ts: SCRIPTC_TEST_SHARD="i/n" slices case lists by sha1(name) mod n — stable across corpus growth, every case in exactly one shard, unset means everything
- differential, llvm-differential, npm, and server harnesses slice through it; the llvm tier-floor assertion checks only this shard's floor programs
- shard.test.ts pins the partition contract (union exact, disjoint, key-stable, env-driven default) and stays green with the job-wide env set
Chris Tate