The test set the file's read bit off via setReadable(false), but on the
Gitea CI runner (root inside the container) the OS ignores that bit and
opens the file anyway, so the test asserted on a condition it never
actually created (LeadContextGaugeTest.java:142 UNKNOWN vs OK, CI run
1887 job 3104, commit fa62e99 on main).
Add Files.isReadable(file) after setReadable(false) and before the gauge
runs, and assumeFalse on it: a skip means "could not set up the case",
never "the behaviour is fine". Restores the read bit either way so
@TempDir cleanup still works.