refactor: add exception subclasses used by core services

FileStorageError, RayActorError, ToolExecutionError, and UnexpectedError
moved here from phase-2 since this is where they are first raised.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: paultranvan

openrag/utils/exceptions/__init__.py

@@ -1 +1,2 @@
 from .base import *
+from .common import *

openrag/utils/exceptions/common.py

@@ -0,0 +1,29 @@
+from .base import OpenRAGError
+
+
+class FileStorageError(OpenRAGError):
+    """Raised when file I/O operations fail (save, read, delete)."""
+
+    def __init__(self, message: str, **kwargs):
+        super().__init__(message=message, code="FILE_STORAGE_ERROR", status_code=500, **kwargs)
+
+
+class RayActorError(OpenRAGError):
+    """Raised when a Ray actor operation fails."""
+
+    def __init__(self, message: str, **kwargs):
+        super().__init__(message=message, code="RAY_ACTOR_ERROR", status_code=500, **kwargs)
+
+
+class ToolExecutionError(OpenRAGError):
+    """Raised when tool execution fails."""
+
+    def __init__(self, message: str, **kwargs):
+        super().__init__(message=message, code="TOOL_EXECUTION_ERROR", status_code=500, **kwargs)
+
+
+class UnexpectedError(OpenRAGError):
+    """Raised for unexpected errors that don't match any specific category."""
+
+    def __init__(self, message: str, **kwargs):
+        super().__init__(message=message, code="UNEXPECTED_ERROR", status_code=500, **kwargs)