v3 世系: 会话崩溃 - 等待中的无效上下文 ActivePage 当 CDP 运输中途空出时( RCA + 补丁, sucker- pick target for v3 release)

Cross-posted from the archived Python SDK repo: https://GitHub.com/Browserbase/stagehand-Python/issues/349 reported a session crash - "Cannot read properties of null (reading 'awaitActivePage')" during act() after rapid CDP cycles. That repo is now archived (no one can reply there), so filing the RCA + patch here as a cherry-pick target for a v3 release. This is v3 lineage, not a demand on v4 - the Python SDK bundles and runs the v3 server, so Python users still hit this.