refactor(session-log): delete dead _clean_session_content helper

Only caller was the removed _save_session_log. Also removes the unused
convert_scratchpad_to_think and has_incomplete_scratchpad imports from
run_agent.py (both still used elsewhere via their own imports).

run_agent.py

@@ -168,7 +168,6 @@ from agent.tool_result_classification import (
     file_mutation_result_landed,
 )
 from agent.trajectory import (
-    convert_scratchpad_to_think, has_incomplete_scratchpad,
     save_trajectory as _save_trajectory_to_file,
 )
 from agent.message_sanitization import (
@@ -1505,16 +1504,6 @@ class AIAgent:
         from agent.agent_runtime_helpers import dump_api_request_debug
         return dump_api_request_debug(self, api_kwargs, reason=reason, error=error)
 
-    @staticmethod
-    def _clean_session_content(content: str) -> str:
-        """Convert REASONING_SCRATCHPAD to think tags and clean up whitespace."""
-        if not content:
-            return content
-        content = convert_scratchpad_to_think(content)
-        content = re.sub(r'\n+(<think>)', r'\n\1', content)
-        content = re.sub(r'(</think>)\n+', r'\1\n', content)
-        return content.strip()
-
 
     def interrupt(self, message: str = None) -> None:
         """

tests/run_agent/test_run_agent.py

@@ -554,25 +554,6 @@ class TestExtractReasoning:
         assert result == "from structured field"
 
 
-class TestCleanSessionContent:
-    def test_none_passthrough(self):
-        assert AIAgent._clean_session_content(None) is None
-
-    def test_scratchpad_converted(self):
-        text = "<REASONING_SCRATCHPAD>think</REASONING_SCRATCHPAD> answer"
-        result = AIAgent._clean_session_content(text)
-        assert "<REASONING_SCRATCHPAD>" not in result
-        assert "<think>" in result
-
-    def test_extra_newlines_cleaned(self):
-        text = "\n\n\n<think>x</think>\n\n\nafter"
-        result = AIAgent._clean_session_content(text)
-        # Should not have excessive newlines around think block
-        assert "\n\n\n" not in result
-        # Content after think block must be preserved
-        assert "after" in result
-
-
 class TestGetMessagesUpToLastAssistant:
     def test_empty_list(self, agent):
         assert agent._get_messages_up_to_last_assistant([]) == []