ensureGitIdentityOnWorkDisk, writeGitIdentity, runFileSync, and
copyHostDir all dropped their mount + sudo install/mkdir/chmod/chown
scaffolding. Every write now goes through MkdirExt4,
WriteExt4FileOwned, ReadExt4File, and the new MkdirAllExt4 helper —
all sudoless against user-owned ext4 images.
Net effect with the prior two commits: ensureWorkDisk, authsync, image
seeding, git identity sync, and file_sync no longer mount the work
disk or spawn sudo mkdir/chmod/chown/cat/install. Only the
image-build path (which legitimately produces root-owned artifacts)
still touches MountTempDir.
The filesystemRunner test harness grew a small debugfs/e2cp/e2rm
emulator so the WorkspaceService tests keep exercising their real
code paths without a live ext4 image. The mock is deliberately
dumb — it only implements the subset runFileSync and writeGitIdentity
drive.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>