- Add should_cancel callback parameter to BFS, DFS, and BestFirst strategies
- Add cancel() method for immediate cancellation (thread-safe)
- Add cancelled property to check cancellation status
- Add _check_cancellation() internal method supporting both sync/async callbacks
- Reset cancel event on strategy reuse for multiple crawls
- Include cancelled flag in state notifications via on_state_change
- Handle callback exceptions gracefully (fail-open, log warning)
- Add comprehensive test suite with 26 tests covering all edge cases
This enables external callers (e.g., cloud platforms) to stop a running
deep crawl mid-execution and retrieve partial results.
Add optional resume_state and on_state_change parameters to all deep
crawl strategies (BFS, DFS, Best-First) for cloud deployment crash
recovery.
Features:
- resume_state: Pass saved state to resume from checkpoint
- on_state_change: Async callback fired after each URL for real-time
state persistence to external storage (Redis, DB, etc.)
- export_state(): Get last captured state manually
- Zero overhead when features are disabled (None defaults)
State includes visited URLs, pending queue/stack, depths, and
pages_crawled count. All state is JSON-serializable.
