feat(ai): services partages A2 + SSE streaming B4 + confirmations UI B5 (#79)

backend/services/errors.py

@@ -0,0 +1,29 @@
+"""Domain errors shared by the reusable service layer.
+
+Services are transport-agnostic: they raise :class:`ServiceError` carrying a
+stable ``code`` and an HTTP ``status`` hint. The REST layer maps it to an
+``HTTPException`` (via the global handler in ``backend.main``) while the tool
+layer maps it to a :class:`backend.tools.context.ToolError`.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+
+class ServiceError(Exception):
+    """Base error for the shared business-logic services."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        code: str = "service_error",
+        status: int = 400,
+        details: dict[str, Any] | None = None,
+    ):
+        super().__init__(message)
+        self.message = message
+        self.code = code
+        self.status = status
+        self.details = details or {}