fix: reuse shared atomic session log helper

run_agent.py

@@ -28,7 +28,6 @@ import json
 import logging
 logger = logging.getLogger(__name__)
 import os
-import tempfile
 import random
 import re
 import sys
@@ -101,6 +100,7 @@ from agent.trajectory import (
     convert_scratchpad_to_think, has_incomplete_scratchpad,
     save_trajectory as _save_trajectory_to_file,
 )
+from utils import atomic_json_write
 
 HONCHO_TOOL_NAMES = {
     "honcho_context",
@@ -1399,17 +1399,12 @@ class AIAgent:
                 "messages": cleaned,
             }
 
-            tmp_dir = str(self.session_log_file.parent) if hasattr(self.session_log_file, 'parent') else os.path.dirname(str(self.session_log_file))
+            atomic_json_write(
-            fd, tmp_path = tempfile.mkstemp(dir=tmp_dir, suffix='.tmp', prefix='.session_')
+                self.session_log_file,
-            try:
+                entry,
-                with os.fdopen(fd, 'w', encoding='utf-8') as f:
+                indent=2,
-                    json.dump(entry, f, indent=2, ensure_ascii=False, default=str)
+                default=str,
-                    f.flush()
+            )
-                    os.fsync(f.fileno())
-                os.replace(tmp_path, str(self.session_log_file))
-            except:
-                os.unlink(tmp_path)
-                raise
 
         except Exception as e:
             if self.verbose_logging:

tests/test_atomic_json_write.py

@@ -97,6 +97,17 @@ class TestAtomicJsonWrite:
         text = target.read_text()
         assert '    "a"' in text  # 4-space indent
 
+    def test_accepts_json_dump_default_hook(self, tmp_path):
+        class CustomValue:
+            def __str__(self):
+                return "custom-value"
+
+        target = tmp_path / "custom_default.json"
+        atomic_json_write(target, {"value": CustomValue()}, default=str)
+
+        result = json.loads(target.read_text(encoding="utf-8"))
+        assert result == {"value": "custom-value"}
+
     def test_unicode_content(self, tmp_path):
         target = tmp_path / "unicode.json"
         data = {"emoji": "🎉", "japanese": "日本語"}

tests/test_run_agent.py

@@ -1928,6 +1928,24 @@ class TestSafeWriter:
         assert inner.getvalue() == "test"
 
 
+class TestSaveSessionLogAtomicWrite:
+    def test_uses_shared_atomic_json_helper(self, agent, tmp_path):
+        agent.session_log_file = tmp_path / "session.json"
+        messages = [{"role": "user", "content": "hello"}]
+
+        with patch("run_agent.atomic_json_write", create=True) as mock_atomic_write:
+            agent._save_session_log(messages)
+
+        mock_atomic_write.assert_called_once()
+        call_args = mock_atomic_write.call_args
+        assert call_args.args[0] == agent.session_log_file
+        payload = call_args.args[1]
+        assert payload["session_id"] == agent.session_id
+        assert payload["messages"] == messages
+        assert call_args.kwargs["indent"] == 2
+        assert call_args.kwargs["default"] is str
+
+
 # ===================================================================
 # Anthropic adapter integration fixes
 # ===================================================================

utils.py

@@ -9,17 +9,25 @@ from typing import Any, Union
 import yaml
 
 
-def atomic_json_write(path: Union[str, Path], data: Any, *, indent: int = 2) -> None:
+def atomic_json_write(
+    path: Union[str, Path],
+    data: Any,
+    *,
+    indent: int = 2,
+    **dump_kwargs: Any,
+) -> None:
     """Write JSON data to a file atomically.
 
     Uses temp file + fsync + os.replace to ensure the target file is never
-    left in a partially-written state.  If the process crashes mid-write,
+    left in a partially-written state. If the process crashes mid-write,
     the previous version of the file remains intact.
 
     Args:
         path: Target file path (will be created or overwritten).
         data: JSON-serializable data to write.
         indent: JSON indentation (default 2).
+        **dump_kwargs: Additional keyword args forwarded to json.dump(), such
+            as default=str for non-native types.
     """
     path = Path(path)
     path.parent.mkdir(parents=True, exist_ok=True)
@@ -31,7 +39,13 @@ def atomic_json_write(path: Union[str, Path], data: Any, *, indent: int = 2) ->
     )
     try:
         with os.fdopen(fd, "w", encoding="utf-8") as f:
-            json.dump(data, f, indent=indent, ensure_ascii=False)
+            json.dump(
+                data,
+                f,
+                indent=indent,
+                ensure_ascii=False,
+                **dump_kwargs,
+            )
             f.flush()
             os.fsync(f.fileno())
         os.replace(tmp_path, path)