fix(ai): creation dossier+fichier en mode agent (BUG-050)

backend/services/mutations.py

@@ -131,18 +131,33 @@ def create_file(
     return {"success": True, "vault": vault_name, "path": rel_path, "size": len(content)}
 
 
-def create_directory(vault_name: str, path: str) -> dict[str, Any]:
+def create_directory(vault_name: str, path: str, *, exist_ok: bool = False) -> dict[str, Any]:
     """Create a directory (and its parents) in a vault.
 
+    Args:
+        vault_name: Name of the vault.
+        path: Vault-relative path of the new directory.
+        exist_ok: When True, an existing directory is a success (idempotent)
+            instead of raising ``already_exists``. Used by the AI tool layer so
+            a "create folder then create file" plan does not fail when the
+            folder is already there (``create_file`` creates parents anyway).
+
     Raises:
         ServiceError: ``not_found`` (404), ``read_only`` (403) or
-            ``already_exists`` (409).
+            ``already_exists`` (409) when *exist_ok* is False.
     """
     root = get_vault_root(vault_name)
     _ensure_writable(root)
     dir_path = resolve_safe_path(root, path)
 
     if dir_path.exists():
+        if exist_ok and dir_path.is_dir():
+            return {
+                "success": True,
+                "vault": vault_name,
+                "path": _rel(root, dir_path),
+                "existed": True,
+            }
         raise ServiceError(
             f"Directory already exists: {path}",
             code="already_exists",