Preflight runs on macOS only, so behaviour that differs on Linux reaches CI first: on 2026-10-16 and 17 three such failures cost a merge-queue round each: a test expecting git's wording for a broken .git file (Linux git prints '(null)'), a test argument over Linux's 128 KiB limit, and test fixtures committing in a bare repository with no git identity (macOS falls back to user@host, Linux refuses).

Preflight runs on macOS only, so behaviour that differs on Linux reaches CI first: on 2026-10-16 and 17 three such failures cost a merge-queue round each: a test expecting git's wording for a broken .git file (Linux git prints '(null)'), a test argument over Linux's 128 KiB limit, and test fixtures committing in a bare repository with no git identity (macOS falls back to user@host, Linux refuses).

Checked at the default branch 2026-10-28

Half the remedy is in: internal/gittest/shim.go gives the git shim a mode that names no gitfile target. Still open: no preflight step runs the tests under Linux, so a Linux-only failure still first shows in CI.