diff --git a/acp_adapter/session.py b/acp_adapter/session.py
index d6dace66b4..61d06432a7 100644
--- a/acp_adapter/session.py
+++ b/acp_adapter/session.py
@@ -466,17 +466,10 @@ class SessionManager:
                 except Exception:
                     logger.debug("Failed to update ACP session metadata", exc_info=True)
 
-            # Replace stored messages with current history.
-            db.clear_messages(state.session_id)
-            for msg in state.history:
-                db.append_message(
-                    session_id=state.session_id,
-                    role=msg.get("role", "user"),
-                    content=msg.get("content"),
-                    tool_name=msg.get("tool_name") or msg.get("name"),
-                    tool_calls=msg.get("tool_calls"),
-                    tool_call_id=msg.get("tool_call_id"),
-                )
+            # Replace stored messages with current history atomically so a
+            # mid-rewrite failure rolls back and the previously persisted
+            # conversation is preserved (salvaged from #13675).
+            db.replace_messages(state.session_id, state.history)
         except Exception:
             logger.warning("Failed to persist ACP session %s", state.session_id, exc_info=True)