Replaces the source-extraction harness (regex-lifting the function body and
asserting 'readlink -m' is present in the text) with the script's own
--self-test-gate entry point, and adds the canonical-root + symlinked-target
spelling from the #108867 report. Two invariant tests, linux_only.
- Rewrite the linux_gate comment to describe the environment fact
(symlinked /home, kernel-canonicalised /proc/<pid>/exe) without
local-patch markers or the unfiled-issue reference.
- Add test_empty_relaunch_target_falls_to_skew pinning the [ -n ... ]
guard behavior so it cannot be simplified away.
- Add the missing trailing newline to the test file.
The linux relaunch gate compares the running desktop's exe path
(relaunch target, read from /proc/<pid>/exe — kernel-canonicalised)
against the checkout's unpacked-app prefix with a raw case-pattern.
On hosts where /home is a symlink to /var/home (e.g. Fedora), the two
sides spell the same tree differently (/home/... vs /var/home/...) and
the gate false-positives "skew", telling the user to reinstall the
desktop app after every successful self-update.
Canonicalise both sides with readlink -m (which resolves existing
leading components without requiring the full path to exist, unlike
-f) before the prefix compare. No-op when both sides already agree.
Teknium