refactors

backend/exceptions.py

@@ -0,0 +1,61 @@
+"""Standardized API exception classes for consistent error responses.
+
+Note: These exceptions use string detail for backward compatibility with existing tests.
+Future refactoring could standardize on structured error responses.
+"""
+
+from fastapi import HTTPException, status
+
+
+class APIError(HTTPException):
+    """Base API error with consistent structure.
+
+    Uses string detail for backward compatibility with existing tests.
+    """
+
+    def __init__(
+        self,
+        status_code: int,
+        message: str,
+    ):
+        super().__init__(status_code=status_code, detail=message)
+
+
+class NotFoundError(APIError):
+    """Resource not found error (404)."""
+
+    def __init__(self, resource: str):
+        super().__init__(
+            status_code=status.HTTP_404_NOT_FOUND,
+            message=f"{resource} not found",
+        )
+
+
+class ConflictError(APIError):
+    """Conflict error (409)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_409_CONFLICT,
+            message=message,
+        )
+
+
+class BadRequestError(APIError):
+    """Bad request error (400)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            message=message,
+        )
+
+
+class ServiceUnavailableError(APIError):
+    """Service unavailable error (503)."""
+
+    def __init__(self, message: str):
+        super().__init__(
+            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+            message=message,
+        )