diff --git a/acp_adapter/session.py b/acp_adapter/session.py
index d6dace66b4e..61d06432a71 100644
--- a/acp_adapter/session.py
+++ b/acp_adapter/session.py
@@ -466,17 +466,10 @@ def _persist(self, state: SessionState) -> None:
                 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)
 
diff --git a/scripts/release.py b/scripts/release.py
index 1b795c27d31..231b5d7090e 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -56,6 +56,7 @@
     "657290301@qq.com": "IMHaoyan",
     "revar@users.noreply.github.com": "revaraver",
     "dengtaoyuan@dengtaoyuandeMac-mini.local": "dengtaoyuan450-a11y",
+    "ysfalweshcan@gmail.com": "Junass1",
     "beardthelion@users.noreply.github.com": "beardthelion",
     "tangyuanjc@JCdeAIfenshendeMac-mini.local": "tangyuanjc",
     "leon@agentlinker.ai": "agentlinker",
diff --git a/tests/acp/test_session.py b/tests/acp/test_session.py
index 03d5f3f658c..60a006b2a8c 100644
--- a/tests/acp/test_session.py
+++ b/tests/acp/test_session.py
@@ -188,6 +188,31 @@ def test_list_sessions_hides_empty_threads(self, manager):
         manager.create_session(cwd="/empty")
         assert manager.list_sessions() == []
 
+    def test_save_session_preserves_existing_messages_on_encode_failure(self, manager):
+        """Regression for #13675: a bad message in state.history must not
+        clobber the previously-persisted transcript.  replace_messages()
+        wraps DELETE + INSERT in a single rolled-back-on-exception txn.
+        """
+        state = manager.create_session()
+        state.history.append({"role": "user", "content": "original"})
+        manager.save_session(state.session_id)
+
+        # Now swap history with a message whose tool_calls is non-JSON-serializable.
+        # _execute_write rolls back; the previously persisted "original" stays.
+        state.history = [
+            {"role": "user", "content": "replacement"},
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [{"bad": object()}],
+            },
+        ]
+        manager.save_session(state.session_id)
+
+        db = manager._get_db()
+        messages = db.get_messages_as_conversation(state.session_id)
+        assert messages == [{"role": "user", "content": "original"}]
+
     def test_cleanup_clears_all(self, manager):
         s1 = manager.create_session()
         s2 = manager.create_session()