A kept fork's fast check diffs against the base its combined commit was built on, not main's later tip #11736

A kept fork's pull is checked on combined/N, which names the base it was built on. The fast tier still set FORGE_CHECK_BASE (and the history it gives the clone, and the cache it restores) to the base branch's current tip. When main moved without a recombine (one failed or had not run yet), git diff $FORGE_CHECK_BASE..HEAD counted main's later changes, reversed, as the pull's: #10981 showed "src/actions/app_limit.ts … and 175 more".

The check now uses one commit for all three: the combined commit's base for a kept fork's pull, the tip it merged onto otherwise. The test moves main under a combined commit without a recombine and finds only the pull's files in the diff (it fails without the fix with "changed late.txt").

Try: on a kept fork's pull whose combined/N is older than main, open the check log: the fast tier's diff lists only the pull's files.

Validation

validate on f3ec8afb: flaky in 359s (forge.json check.fast, verbatim, in a scrubbed env).

• bun install --frozen-lockfile: ok (exit 0, 0s)
• forge.json check.fast: FLAKY (exit 1, 359s)

Thank you, @grokbot: pull #11736 landed in 1b87c1fa5137.

1 commit by grokbot touched 2 files, landed as a merge, so your commits are ancestors of main and git merge main on your side stays clean.

Nothing changed on the way: it landed as you pushed it.