fix(session): avoid blocking large chat cleanup

tests/test_session_manager_persistence.py

@@ -0,0 +1,104 @@
+from __future__ import annotations
+
+import json
+import os
+import time
+from datetime import datetime
+from pathlib import Path
+
+from nanobot.session.manager import SessionManager
+
+
+def _read_jsonl(path: Path) -> list[dict]:
+    return [
+        json.loads(line)
+        for line in path.read_text(encoding="utf-8").splitlines()
+        if line.strip()
+    ]
+
+
+def test_save_appends_only_new_messages(tmp_path: Path) -> None:
+    manager = SessionManager(tmp_path)
+    session = manager.get_or_create("qq:test")
+    session.add_message("user", "hello")
+    session.add_message("assistant", "hi")
+    manager.save(session)
+
+    path = manager._get_session_path(session.key)
+    original_text = path.read_text(encoding="utf-8")
+
+    session.add_message("user", "next")
+    manager.save(session)
+
+    lines = _read_jsonl(path)
+    assert path.read_text(encoding="utf-8").startswith(original_text)
+    assert sum(1 for line in lines if line.get("_type") == "metadata") == 1
+    assert [line["content"] for line in lines if line.get("role")] == ["hello", "hi", "next"]
+
+
+def test_save_appends_metadata_checkpoint_without_rewriting_history(tmp_path: Path) -> None:
+    manager = SessionManager(tmp_path)
+    session = manager.get_or_create("qq:test")
+    session.add_message("user", "hello")
+    session.add_message("assistant", "hi")
+    manager.save(session)
+
+    path = manager._get_session_path(session.key)
+    original_text = path.read_text(encoding="utf-8")
+
+    session.last_consolidated = 2
+    manager.save(session)
+
+    lines = _read_jsonl(path)
+    assert path.read_text(encoding="utf-8").startswith(original_text)
+    assert sum(1 for line in lines if line.get("_type") == "metadata") == 2
+    assert lines[-1]["_type"] == "metadata"
+    assert lines[-1]["last_consolidated"] == 2
+
+    manager.invalidate(session.key)
+    reloaded = manager.get_or_create("qq:test")
+    assert reloaded.last_consolidated == 2
+    assert [message["content"] for message in reloaded.messages] == ["hello", "hi"]
+
+
+def test_clear_rewrites_session_file(tmp_path: Path) -> None:
+    manager = SessionManager(tmp_path)
+    session = manager.get_or_create("qq:test")
+    session.add_message("user", "hello")
+    session.add_message("assistant", "hi")
+    manager.save(session)
+
+    path = manager._get_session_path(session.key)
+    session.clear()
+    manager.save(session)
+
+    lines = _read_jsonl(path)
+    assert len(lines) == 1
+    assert lines[0]["_type"] == "metadata"
+    assert lines[0]["last_consolidated"] == 0
+
+    manager.invalidate(session.key)
+    reloaded = manager.get_or_create("qq:test")
+    assert reloaded.messages == []
+    assert reloaded.last_consolidated == 0
+
+
+def test_list_sessions_uses_file_mtime_for_append_only_updates(tmp_path: Path) -> None:
+    manager = SessionManager(tmp_path)
+    session = manager.get_or_create("qq:test")
+    session.add_message("user", "hello")
+    manager.save(session)
+
+    path = manager._get_session_path(session.key)
+    stale_time = time.time() - 3600
+    os.utime(path, (stale_time, stale_time))
+
+    before = datetime.fromisoformat(manager.list_sessions()[0]["updated_at"])
+    assert before.timestamp() < time.time() - 3000
+
+    session.add_message("assistant", "hi")
+    manager.save(session)
+
+    after = datetime.fromisoformat(manager.list_sessions()[0]["updated_at"])
+    assert after > before
+