feat: auto-revert incomplete skill edits (#923)

fix: restore _format_error helper for test compatibility (#916)

tools/skill_edit_guard.py

@@ -0,0 +1,122 @@
+"""Skill Edit Guard — Poka-yoke auto-revert for incomplete skill edits.
+
+Creates atomic skill edits with automatic rollback on failure.
+Prevents broken skills from corrupting future sessions.
+
+Usage:
+    from tools.skill_edit_guard import atomic_skill_edit
+    with atomic_skill_edit(skill_path) as editor:
+        editor.write(new_content)
+        # If exception occurs, file is automatically reverted
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+import shutil
+import tempfile
+import time
+from contextlib import contextmanager
+from pathlib import Path
+from typing import Any, Dict, Optional
+
+logger = logging.getLogger(__name__)
+
+
+class SkillEditGuard:
+    """Atomic skill file editing with auto-revert on failure."""
+
+    def __init__(self, skill_path: str):
+        self._path = Path(skill_path)
+        self._backup: Optional[Path] = None
+        self._committed = False
+
+    def backup(self) -> bool:
+        """Create backup before editing."""
+        if not self._path.exists():
+            return True  # New file, nothing to backup
+
+        backup_dir = self._path.parent / ".skill_backups"
+        backup_dir.mkdir(exist_ok=True)
+
+        ts = int(time.time() * 1000)
+        self._backup = backup_dir / f"{self._path.name}.{ts}.bak"
+        shutil.copy2(self._path, self._backup)
+        logger.debug("Skill backup created: %s", self._backup)
+        return True
+
+    def write(self, content: str) -> bool:
+        """Write content with validation. Returns True if valid."""
+        # Validate YAML frontmatter
+        if content.startswith("---"):
+            end = content.find("---", 3)
+            if end < 0:
+                logger.error("Invalid YAML frontmatter: unclosed ---")
+                return False
+
+        # Validate not empty
+        if len(content.strip()) < 10:
+            logger.error("Content too short, likely corrupted")
+            return False
+
+        # Write atomically using temp file
+        tmp = self._path.with_suffix(".tmp")
+        try:
+            tmp.write_text(content, encoding="utf-8")
+            tmp.rename(self._path)
+            return True
+        except Exception as e:
+            logger.error("Write failed: %s", e)
+            if tmp.exists():
+                tmp.unlink()
+            return False
+
+    def commit(self):
+        """Mark edit as successful, remove backup."""
+        self._committed = True
+        if self._backup and self._backup.exists():
+            self._backup.unlink()
+            logger.debug("Skill backup removed: %s", self._backup)
+
+    def rollback(self) -> bool:
+        """Revert to backup."""
+        if self._backup and self._backup.exists():
+            shutil.copy2(self._backup, self._path)
+            self._backup.unlink()
+            logger.warning("Skill reverted from backup: %s", self._path)
+            return True
+        return False
+
+    def __enter__(self):
+        self.backup()
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is not None:
+            self.rollback()
+            return False  # Re-raise exception
+        if not self._committed:
+            self.rollback()
+        return False
+
+
+@contextmanager
+def atomic_skill_edit(skill_path: str):
+    """Context manager for atomic skill editing.
+
+    Usage:
+        with atomic_skill_edit("/path/to/skill/SKILL.md") as editor:
+            success = editor.write(new_content)
+            if not success:
+                raise ValueError("Write failed")
+            # __exit__ commits on success, reverts on exception
+    """
+    guard = SkillEditGuard(skill_path)
+    guard.backup()
+    try:
+        yield guard
+        guard.commit()
+    except Exception:
+        guard.rollback()
+        raise

tools/skill_manager_tool.py

@@ -44,6 +44,34 @@ from typing import Dict, Any, Optional, Tuple
 
 logger = logging.getLogger(__name__)
 
+
+def _format_error(
+    message: str,
+    skill_name: str = None,
+    file_path: str = None,
+    suggestion: str = None,
+    context: dict = None,
+) -> Dict[str, Any]:
+    """Format an error with rich context for better debugging."""
+    parts = [message]
+    if skill_name:
+        parts.append(f"Skill: {skill_name}")
+    if file_path:
+        parts.append(f"File: {file_path}")
+    if suggestion:
+        parts.append(f"Suggestion: {suggestion}")
+    if context:
+        for key, value in context.items():
+            parts.append(f"{key}: {value}")
+    return {
+        "success": False,
+        "error": " | ".join(parts),
+        "skill_name": skill_name,
+        "file_path": file_path,
+        "suggestion": suggestion,
+    }
+
+
 # Import security scanner — agent-created skills get the same scrutiny as
 # community hub installs.
 try: