Fix --output-dir help text and document None mean_entropy

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

Author: kfallah

claas/eval/__main__.py

@@ -75,10 +75,7 @@ def add_eval_arguments(parser: argparse.ArgumentParser) -> None:
     parser.add_argument(
         "--output-dir",
         default=None,
-        help=(
-            "Output directory for results "
-            "(default: auto ./data/evals/<UTC timestamp>)"
-        ),
+        help="Output directory for results (auto-generated if omitted)",
     )
     parser.add_argument(
         "--gemini-api-key",

claas/eval/types.py

@@ -68,6 +68,7 @@ class SDPOMetrics:
 class CollapseMetrics:
     """Collapse detection metrics."""
 
+    # None in Tinker mode — proxy doesn't expose the full token distribution
     mean_entropy: float | None = None
     mean_logprob: float = 0.0
     entropy_ratio_to_baseline: float | None = None