fix(#4783): mtime probe follows symlinked skill dirs to match compute path (gate finding 3)

Codex round-3 reproduced: _skill_tree_max_mtime_ns used os.walk(followlinks=False)
while the compute path iter_skill_index_files uses followlinks=True, so an edit to
a symlinked skill's target SKILL.md was invisible to the probe (stale up to TTL).
Added followlinks=True to the probe walk so it descends symlinked skill dirs and
sees target mtime changes. Regression test added + proven non-vacuous.

Co-authored-by: Rod Boev <rod.boev@gmail.com>

api/profiles.py

@@ -1597,7 +1597,10 @@ def _skill_tree_max_mtime_ns(skills_dir: Path, config_path: Path) -> int:
         return max_ns
     try:
         # Directory mtimes catch nested out-of-band deletes that leave file mtimes unchanged.
-        for root, dirnames, filenames in os.walk(skills_dir):
+        # followlinks=True mirrors agent.skill_utils.iter_skill_index_files (the compute
+        # path), so a symlinked skill directory is descended into and edits to its target
+        # SKILL.md change the probe value — otherwise such edits would stay stale up to the TTL.
+        for root, dirnames, filenames in os.walk(skills_dir, followlinks=True):
             root_path = Path(root)
             try:
                 max_ns = max(max_ns, root_path.stat().st_mtime_ns)

tests/test_issue4783_profile_skills_mtime_cache.py

@@ -308,6 +308,42 @@ class TestNestedDeletionDetected:
         assert result == (1, 1)
 
 
+class TestSymlinkedSkillProbeFollowsLinks:
+    """The mtime probe must follow symlinked skill directories the same way the
+    compute path (iter_skill_index_files, followlinks=True) does — otherwise an
+    edit to a symlinked skill's target SKILL.md is invisible to the probe and
+    the counts stay stale up to the TTL (gate finding)."""
+
+    def test_symlinked_skill_target_edit_changes_probe(self, profiles_mod, tmp_path):
+        mod, profile_dir = profiles_mod
+        skills_dir = profile_dir / "skills"
+        skills_dir.mkdir(parents=True, exist_ok=True)
+        config_path = profile_dir / "config.yaml"
+
+        # Real skill living OUTSIDE the profile, linked in via a symlinked dir.
+        target = tmp_path / "external-skill"
+        target.mkdir()
+        skill_md = target / "SKILL.md"
+        skill_md.write_text("---\nname: linked\n---\n# linked\n", encoding="utf-8")
+        link = skills_dir / "linked"
+        try:
+            link.symlink_to(target, target_is_directory=True)
+        except (OSError, NotImplementedError):
+            import pytest
+            pytest.skip("symlinks not supported on this platform")
+
+        before = mod._skill_tree_max_mtime_ns(skills_dir, config_path)
+        # Edit the target SKILL.md (bump its mtime well past granularity).
+        import os as _os
+        future = time.time() + 100
+        _os.utime(skill_md, (future, future))
+        after = mod._skill_tree_max_mtime_ns(skills_dir, config_path)
+
+        assert after > before, (
+            "probe must follow the symlinked skill dir and see the target SKILL.md mtime change"
+        )
+
+
 class TestReturnSignature:
     """Proof matrix row 6: return signature is tuple[int, int]."""