The crawler's default session pool is SessionPool() with persistence_enabled=False (_basic_crawler.py, sessions/_session_pool.py), so sessions and their cookies are lost on migration. In JS v4, session pool persistence is on by default.

Turn persistence on by default, with a persistence key derived from the crawler ID, so that several crawlers in one process do not overwrite each other's state.

This will be a breaking change.

JS implementation: apify/crawlee#4068. Related: #2301 (ownership of injected pools), #2298 (proxy persisted with the session).

✍️ Drafted by Claude Code