- popstate handler now refuses to switch sessions mid-stream (S.busy guard)
Mirrors the same guard the cross-tab storage handler had. PR #1392 added
the popstate listener but missed this. Without it, browser Back during
a live stream silently yanks the user out of their turn.
(Opus pre-release advisor finding)
- CHANGELOG entry for v0.50.254 (4 PRs + 1 Opus follow-up)
1 regression test in test_v050254_opus_followups.py.
