ff835bfba1acac5d2e56dc7d47dc0e7896051c78  REGRESSION(320518@main): WebDriver returns 'no such element' instead of 'stale element reference' for a node reference from a previous document

Classified as not security-relevant.
Triage note: Adds m_knownNodeReferences bookkeeping in WebAutomationSession/Proxy (Add/IsKnownNodeReference IPC, transfer on commitProvisionalPage, JS isKnownReference/addKnownReference) so a reference survives a browsing-context-group swap and reports StaleNode vs NodeNotFound correctly. WebDriver automation feature/correctness, not a web-content-reachable sandbox security bug.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+6.47), bounds_guard (+3.25), null_guard (+2.59), msg_feature (-1.0), large_churn (-2.0)