clan-app: full context tracebacks

If an exception now is thrown in one of the middlewares we will get a
proper traceback instead of a cut off one like before

pkgs/clan-app/clan_app/middleware/base.py

@@ -12,6 +12,25 @@ class MiddlewareContext:
     request: "BackendRequest"
     bridge: "ApiBridge"
     exit_stack: ExitStack
+    original_traceback: list[str]
+
+
+class MiddlewareError(Exception):
+    """Exception that preserves original calling context."""
+
+    def __init__(
+        self, message: str, original_frames: list[str], original_error: Exception
+    ) -> None:
+        # Store just the original error message for API responses
+        super().__init__(str(original_error))
+        self.method_message = message
+        self.original_frames = original_frames
+        self.original_error = original_error
+
+    def __str__(self) -> str:
+        # For traceback display, show in proper Python traceback order (oldest to newest)
+        original_context = "".join(self.original_frames)
+        return f"Traceback (most recent call last):\n{original_context.rstrip()}\nMethodExecutionError: {self.original_error}"
 
 
 @dataclass(frozen=True)