Automatically detect when crawls are blocked by anti-bot systems
(Akamai, Cloudflare, PerimeterX, DataDome, Imperva, etc.) and
escalate through configurable retry and fallback strategies.
New features on CrawlerRunConfig:
- max_retries: retry rounds when blocking is detected
- fallback_proxy_configs: list of fallback proxies tried each round
- fallback_fetch_function: async last-resort function returning raw HTML
New field on ProxyConfig:
- is_fallback: skip proxy on first attempt, activate only when blocked
Escalation chain per round: main proxy → fallback proxies in order.
After all rounds: fallback_fetch_function as last resort.
Detection uses tiered heuristics — structural HTML markers (high
confidence) trigger on any page, generic patterns only on short
error pages to avoid false positives.
