chmod: recursive mode returns exit code 0 even when some files fail (last-file-wins)

In Chmoder::chmod() the recursive branch overwrites the running result instead of accumulating it, so the exit code reflects only the last file processed:

if self.recursive {
    r = self.walk_dir_with_context(file, true);   // overwrites r
} else {
    r = self.chmod_file(file).and(r);
}

PoC: GNU returns 1 when a file fails; uutils returns 0 if the last entry succeeds:

$ chmod -R 0755 chmod-bug/root chmod-bug/user  # GNU -> ret=1
$ uutils chmod -R 0755 chmod-bug/root chmod-bug/user  # -> ret=0

Impact: scripts relying on the exit code get a false success signal while some files retained restrictive/unexpected permissions, leading to access-control misconfigurations. Recommendation: accumulate errors during traversal.

Remediation: Acknowledged by Canonical; fixed in commit abd581f6.

Reported by Zellic in the uutils coreutils Program Security Assessment (prepared for Canonical, Jan 20 2026), audited commit 3a07ffc5a9bd4c283e75afa548ba1f1957bad242. Finding 3.2. Credit: Zellic.