Codex round-4 found my followlinks=True change introduced a perf regression: the
probe os.walk lacked the .git/.venv/node_modules/site-packages + skill-support-dir
pruning that iter_skill_index_files applies, so a skill vendoring a dependency
tree made this EVERY-CALL probe walk thousands of irrelevant files — defeating the
cache's whole purpose. The probe now prunes dirnames[:] with the same
EXCLUDED_SKILL_DIRS + SKILL_SUPPORT_DIRS sets as the compute path. Regression test
(change deep inside node_modules/ must not move the probe) added + non-vacuous.
Co-authored-by: Rod Boev <rod.boev@gmail.com>