fix: address twenty-second round of Copilot PR review feedback

- Fix PS1 temp file leak: clean up pyStderrFile in catch block so temp
  files don't accumulate when Python invocation throws
- Document skill-agent reconciliation strategy: expanded docstring on
  _register_for_non_skill_agents explaining the full removal/install
  flow and why skill agents are handled separately via
  _unregister_skills + _reconcile_skills

Author: mnriem

scripts/powershell/common.ps1

@@ -455,6 +455,7 @@ except Exception:
                         Remove-Item $pyStderrFile -Force -ErrorAction SilentlyContinue
                     } catch {
                         $strategy = 'replace'
+                        if ($pyStderrFile) { Remove-Item $pyStderrFile -Force -ErrorAction SilentlyContinue }
                     }
                 }
                 # Try manifest file path first, then convention path

src/specify_cli/presets.py

@@ -768,12 +768,18 @@ def _register_for_non_skill_agents(
         source_id: str,
         source_dir: Path,
     ) -> None:
-        """Register commands for all agents during reconciliation.
-
-        Uses the non-skill registrar for command agents, then relies on
-        _reconcile_skills() (called separately) to properly format SKILL.md
-        files for skill-based agents. This avoids overwriting properly
-        formatted SKILL.md content with raw command file content.
+        """Register commands for non-skill agents during reconciliation.
+
+        Skill-based agents (``/SKILL.md`` layout) are handled separately:
+        - On removal: ``_unregister_skills()`` restores from core/extension,
+          then ``_reconcile_skills()`` re-runs ``_register_skills()`` for the
+          next winning preset so SKILL.md files get proper frontmatter and
+          descriptions.
+        - On install: ``_register_skills()`` writes formatted SKILL.md, then
+          ``_reconcile_skills()`` ensures the actual priority winner is used.
+
+        Writing raw command content to skill agents would produce invalid
+        SKILL.md files (missing skill frontmatter, descriptions, etc.).
         """
         registrar.register_commands_for_non_skill_agents(
             commands, source_id, source_dir, self.project_root