fix(gateway): make Telegram DM topic config writes atomic

gateway/platforms/telegram.py

@@ -11,6 +11,7 @@ import asyncio
 import json
 import logging
 import os
+import tempfile
 import html as _html
 import re
 from typing import Dict, List, Optional, Any
@@ -534,8 +535,23 @@ class TelegramAdapter(BasePlatformAdapter):
                         break
 
             if changed:
-                with open(config_path, "w") as f:
-                    _yaml.dump(config, f, default_flow_style=False, sort_keys=False)
+                fd, tmp_path = tempfile.mkstemp(
+                    dir=str(config_path.parent),
+                    suffix=".tmp",
+                    prefix=".config_",
+                )
+                try:
+                    with os.fdopen(fd, "w", encoding="utf-8") as f:
+                        _yaml.dump(config, f, default_flow_style=False, sort_keys=False)
+                        f.flush()
+                        os.fsync(f.fileno())
+                    os.replace(tmp_path, config_path)
+                except BaseException:
+                    try:
+                        os.unlink(tmp_path)
+                    except OSError:
+                        pass
+                    raise
                 logger.info(
                     "[%s] Persisted thread_id=%s for topic '%s' in config.yaml",
                     self.name, thread_id, topic_name,

tests/gateway/test_dm_topics.py

@@ -283,6 +283,48 @@ def test_persist_dm_topic_thread_id_skips_if_already_set(tmp_path):
 # ── _get_dm_topic_info ──
 
 
+def test_persist_dm_topic_thread_id_preserves_config_on_write_failure(tmp_path):
+    """Failed writes should leave the original config.yaml intact."""
+    import yaml
+
+    config_data = {
+        "platforms": {
+            "telegram": {
+                "extra": {
+                    "dm_topics": [
+                        {
+                            "chat_id": 111,
+                            "topics": [
+                                {"name": "General", "icon_color": 123},
+                            ],
+                        }
+                    ]
+                }
+            }
+        }
+    }
+
+    config_file = tmp_path / ".hermes" / "config.yaml"
+    config_file.parent.mkdir(parents=True)
+    original_text = yaml.dump(config_data)
+    config_file.write_text(original_text, encoding="utf-8")
+
+    adapter = _make_adapter()
+
+    def fail_dump(*args, **kwargs):
+        raise RuntimeError("boom")
+
+    with patch.object(Path, "home", return_value=tmp_path), \
+         patch.dict(os.environ, {"HERMES_HOME": str(tmp_path / ".hermes")}), \
+         patch("yaml.dump", side_effect=fail_dump):
+        adapter._persist_dm_topic_thread_id(111, "General", 999)
+
+    assert config_file.read_text(encoding="utf-8") == original_text
+    result = yaml.safe_load(config_file.read_text(encoding="utf-8"))
+    topics = result["platforms"]["telegram"]["extra"]["dm_topics"][0]["topics"]
+    assert "thread_id" not in topics[0]
+
+
 def test_get_dm_topic_info_finds_cached_topic():
     """Should return topic config when thread_id is in cache."""
     adapter = _make_adapter([