fix: create skills directory on demand during extension/preset install (#2711)

* fix: create skills directory on demand during extension/preset install

_get_skills_dir() in both extensions.py and presets.py returned None
when the skills directory did not yet exist on disk, even though skills
were enabled in init-options. This caused extension skill registration
to silently produce an empty registered_skills list and skip writing
SKILL.md files.

Replace the is_dir() bail-out with mkdir(parents=True, exist_ok=True)
so the directory is created on demand when ai_skills is enabled.

Update the existing test expectation and add a parametrized regression
test (claude + codex) that installs an extension before the skills
directory exists and asserts SKILL.md files and registry entries are
created.

Fixes #2682

* test: assert skills dir is NOT created when skills are disabled

Strengthen negative tests to verify _get_skills_dir does not create the
directory on disk when ai_skills is false or init-options.json is absent.

* fix: add symlink/containment check and preserve Kimi existence gate

Address PR review feedback:

- Use _ensure_safe_shared_directory() instead of raw mkdir() to prevent
  symlink-following writes outside the project root.
- Restore the is_dir() existence gate for the Kimi native-skills
  fallback (ai_skills=false): only create the directory on demand when
  ai_skills is explicitly enabled.
- Update docstrings to reflect the on-demand vs existence-gate behavior.
- Reuse resolve_skills_dir helper in tests instead of manually
  reconstructing paths from AGENT_CONFIG.

* refactor: extract resolve_active_skills_dir shared helper

Deduplicate the _get_skills_dir logic that was nearly identical in
ExtensionManager and PresetManager into a single module-level
resolve_active_skills_dir() function in __init__.py.

The shared helper wraps _ensure_safe_shared_directory errors with
skills-specific messages so users see 'agent skills directory' instead
of 'shared infrastructure directory' in error output.

Both class methods now delegate to the shared helper.

* fix: preserve original error reason in skills dir safety check

Include the original exception message from _ensure_safe_shared_directory
in the re-raised ValueError so the user sees the specific reason (symlink,
not-a-directory, path escape, etc.) instead of a generic message.

* fix: handle skills dir safety errors gracefully during install

Catch ValueError/OSError from _get_skills_dir() inside
_register_extension_skills() so a symlink or permission error logs a
warning and returns [] instead of aborting mid-install and leaving a
partially-installed extension without a registry entry.

Also document OSError in resolve_active_skills_dir() docstring.

* fix: catch errors in _get_skills_dir and use _print_cli_warning

Move the ValueError/OSError catch from _register_extension_skills into
_get_skills_dir itself so all callers (install, uninstall, reconcile)
are protected from unsafe-path exceptions.

Replace logging.getLogger().warning with _print_cli_warning for
consistent Rich-formatted user output.

* fix: use context-aware error messages for skills directory safety

Add a 'context' parameter to _ensure_safe_shared_directory (defaults to
'shared infrastructure directory' for backward compat). The skills dir
caller passes context='agent skills directory' so error messages say
e.g. 'Refusing to use symlinked agent skills directory' instead of
'Refusing to use symlinked shared infrastructure directory'.

Simplify resolve_active_skills_dir by removing the now-unnecessary
try/except wrapper.

* fix: validate Kimi native-skills directory for symlink/containment

The Kimi fallback path (ai_skills=false) used is_dir() which follows
symlinks, so a symlinked .kimi/skills could cause writes outside the
project root. Now validates with _ensure_safe_shared_directory(create=
False) before returning the directory.

tests/test_extension_skills.py

@@ -173,24 +173,32 @@ class TestExtensionManagerGetSkillsDir:
         assert result == skills_dir
 
     def test_returns_none_when_no_ai_skills(self, no_skills_project):
-        """Should return None when ai_skills is false."""
+        """Should return None when ai_skills is false and not create the dir."""
         manager = ExtensionManager(no_skills_project)
         result = manager._get_skills_dir()
         assert result is None
+        # Ensure the directory was NOT created on disk
+        from specify_cli import _get_skills_dir as resolve_skills_dir
+        skills_path = resolve_skills_dir(no_skills_project, "claude")
+        assert not skills_path.exists()
 
     def test_returns_none_when_no_init_options(self, project_dir):
-        """Should return None when init-options.json is missing."""
+        """Should return None when init-options.json is missing and not create any dir."""
         manager = ExtensionManager(project_dir)
         result = manager._get_skills_dir()
         assert result is None
+        # No agent skills directory should have been created
+        assert not (project_dir / ".claude" / "skills").exists()
+        assert not (project_dir / ".agents" / "skills").exists()
 
-    def test_returns_none_when_skills_dir_missing(self, project_dir):
-        """Should return None when skills dir doesn't exist on disk."""
+    def test_creates_skills_dir_on_demand(self, project_dir):
+        """Should create skills dir when ai_skills is enabled but dir is missing."""
         _create_init_options(project_dir, ai="claude", ai_skills=True)
-        # Don't create the skills directory
+        # Don't create the skills directory — _get_skills_dir should do it
         manager = ExtensionManager(project_dir)
         result = manager._get_skills_dir()
-        assert result is None
+        assert result is not None
+        assert result.is_dir()
 
     def test_returns_kimi_skills_dir_when_ai_skills_disabled(self, project_dir):
         """Kimi should still use its native skills dir when ai_skills is false."""
@@ -460,6 +468,38 @@ class TestExtensionSkillRegistration:
         assert "speckit-missing-cmd-ext-exists" in metadata["registered_skills"]
         assert "speckit-missing-cmd-ext-ghost" not in metadata["registered_skills"]
 
+    @pytest.mark.parametrize("ai", ["claude", "codex"])
+    def test_skills_registered_when_dir_missing(self, project_dir, temp_dir, ai):
+        """Extension add should create skills dir on demand and register skills.
+
+        Regression test for https://github.com/github/spec-kit/issues/2682:
+        when an extension is installed before the agent skills directory exists,
+        skills must still be materialized (the directory is created on demand).
+        """
+        _create_init_options(project_dir, ai=ai, ai_skills=True)
+        # Deliberately do NOT create the skills directory
+        ext_dir = _create_extension_dir(temp_dir, ext_id="early-ext")
+
+        manager = ExtensionManager(project_dir)
+        manifest = manager.install_from_directory(
+            ext_dir, "0.1.0", register_commands=False
+        )
+
+        # Skills dir should have been created automatically
+        from specify_cli import _get_skills_dir as resolve_skills_dir
+        skills_dir = resolve_skills_dir(project_dir, ai)
+        assert skills_dir.is_dir()
+
+        # SKILL.md files should exist
+        assert (skills_dir / "speckit-early-ext-hello" / "SKILL.md").exists()
+        assert (skills_dir / "speckit-early-ext-world" / "SKILL.md").exists()
+
+        # Registry should record them
+        metadata = manager.registry.get(manifest.id)
+        assert len(metadata["registered_skills"]) == 2
+        assert "speckit-early-ext-hello" in metadata["registered_skills"]
+        assert "speckit-early-ext-world" in metadata["registered_skills"]
+
 
 # ===== Extension Skill Unregistration Tests =====