rev-parse --git-common-dir resolves symlinks while ensureIsolation derives
sourceCommonDir lexically from the session cwd (resolveRepository walks
path.resolve'd components). On any symlinked repo path (macOS /tmp,
symlinked project dirs) the lexical comparison missed, detachGitDir
returned "independent", and the parent-mutation leak silently survived.
Realpath both sides before comparing; regression test drives the gate
through a symlink alias.
can1357
df9b04a0eb