The build-runtime matrix lock could be stale-reclaimed by a sibling job in the same workflow run after 10 minutes. That let the x11 job start writing build/pre-built/x86_64-unknown-linux-gnu while headless was still archiving it, producing tar file-changed failures.

Track the current run id while acquiring the lock and never stale-reclaim a holder from the same run. Older-run stale locks still use the existing reclaim path.

Verification:
- git diff --check

Observed on run 221:
- headless build completed and failed only during archive upload due the race
- x11 build passed, including dual-output validation