fix: preserve Luna context-limit error code

Author: deep1725

evaluators/contrib/galileo/README.md

@@ -2,6 +2,14 @@
 
 Integration package for Galileo Luna evaluator.
 
+## Context-limit errors
+
+If the model server rejects an input for exceeding its maximum context length,
+the evaluator returns `metadata.error_code: context_limit`. The server still
+redacts the error message. Clients can use this safe code to report an unsupported
+input separately from transient evaluator failures without exposing internal error
+details or retrying the same oversized input.
+
 ## Migrating from Luna2
 
 The `galileo.luna2` evaluator ID has been removed. Existing controls that use

evaluators/contrib/galileo/src/agent_control_evaluator_galileo/luna/evaluator.py

@@ -359,6 +359,12 @@ def _handle_error(
             **self._base_metadata(),
             "error_type": type(error).__name__,
         }
+        # The server redacts error text, so retain this deterministic failure as
+        # a safe code that clients can distinguish from an evaluator outage.
+        if isinstance(error, RuntimeError) and error_detail.startswith(
+            "Input exceeds maximum length for Galileo model server:"
+        ):
+            metadata["error_code"] = "context_limit"
         if isinstance(error, httpx.HTTPStatusError):
             metadata.update(_http_status_error_metadata(error))