diff --git a/reme/utils/agent_state_io.py b/reme/utils/agent_state_io.py
index adb62d67..be8cfd05 100644
--- a/reme/utils/agent_state_io.py
+++ b/reme/utils/agent_state_io.py
@@ -65,7 +65,9 @@ class AsStateHandler:
     async def load(self) -> AgentState:
         """Read an AgentState back from ``self.path``."""
         async with aiofiles.open(self.path, encoding="utf-8") as f:
-            lines = (await f.read()).splitlines()
+            # Unicode line separators are valid JSON string content, not JSONL delimiters.
+            content = await f.read()
+            lines = content.split("\n") if content else []
         if not lines:
             return AgentState()
 
diff --git a/tests/unit/test_agent_state_io.py b/tests/unit/test_agent_state_io.py
new file mode 100644
index 00000000..df28c5b4
--- /dev/null
+++ b/tests/unit/test_agent_state_io.py
@@ -0,0 +1,56 @@
+"""AgentScope state persistence must follow JSONL record boundaries."""
+
+from pathlib import Path
+
+import pytest
+from agentscope.message import UserMsg
+from agentscope.state import AgentState
+
+from reme.utils import AsStateHandler
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("separator", ["ordinary", "\n", "\r\n", "\u0085", "\u2028", "\u2029"])
+@pytest.mark.parametrize("field", ["summary", "context"])
+async def test_state_round_trip_preserves_text_separators(tmp_path: Path, separator: str, field: str):
+    """Valid Unicode JSON string content never creates an extra JSONL record."""
+    text = f"before{separator}after"
+    state = AgentState(
+        session_id="unicode-session",
+        reply_id="saved-reply",
+        cur_iter=3,
+        summary=text if field == "summary" else "ordinary summary",
+        context=[UserMsg(name="user", content=text if field == "context" else "ordinary message")],
+    )
+    handler = AsStateHandler.for_session(tmp_path, state.session_id)
+
+    await handler.dump(state)
+    restored = await handler.load()
+
+    assert restored.model_dump() == state.model_dump()
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("newline", ["\n", "\r\n"])
+async def test_state_load_accepts_lf_and_crlf_records(tmp_path: Path, newline: str):
+    """Existing LF and CRLF files retain their header and context records."""
+    state = AgentState(session_id="existing-session", summary="summary", context=[UserMsg(name="user", content="text")])
+    handler = AsStateHandler.for_session(tmp_path, state.session_id)
+    await handler.dump(state)
+    content = handler.path.read_text(encoding="utf-8")
+    handler.path.write_bytes(content.replace("\n", newline).encode("utf-8"))
+
+    assert (await handler.load()).model_dump() == state.model_dump()
+
+
+@pytest.mark.asyncio
+async def test_state_load_accepts_empty_file(tmp_path: Path):
+    """An empty state file continues to load as a fresh AgentState."""
+    handler = AsStateHandler.for_session(tmp_path, "empty-session")
+    handler.path.write_text("", encoding="utf-8")
+
+    restored = await handler.load()
+    assert restored.summary == ""
+    assert restored.context == []
+    assert restored.cur_iter == 0
+    assert restored.session_id