refactor(agent): trim recovery tail anchor

nanobot/utils/runtime.py

@@ -14,7 +14,7 @@ _MAX_REPEAT_EXTERNAL_LOOKUPS = 2
 
 # Third same-target workspace violation in a turn escalates to "stop retrying".
 _MAX_REPEAT_WORKSPACE_VIOLATIONS = 2
-_LENGTH_RECOVERY_TAIL_CHARS = 500
+_LENGTH_RECOVERY_TAIL_CHARS = 64
 
 EMPTY_FINAL_RESPONSE_MESSAGE = (
     "I completed the tool steps but couldn't produce a final answer. "

tests/utils/test_runtime.py

@@ -3,7 +3,7 @@ from nanobot.utils.runtime import build_length_recovery_message
 
 def test_length_recovery_message_anchors_the_existing_tail() -> None:
     omitted_prefix = "OMITTED_PREFIX"
-    tail = "x" * 500
+    tail = "x" * 64
 
     message = build_length_recovery_message(omitted_prefix + tail)