After (extended): fix/issue-23653 at 17920a624f (production code identical to 90d4467b8a; later commits are test-only),
same web dev server, page reloaded, same seeded threads, same MutationObserver/focusin logger (driver-live-region-logger.md).
4305ms KEY: ctrl+shift+s settle x2, then ctrl+z (grouped)
5677ms focus: Message Fix login bug
6081ms live(polite): Settled 1 thread, Ctrl+Z to undo
7173ms focus: Message New thread
7494ms live(polite): Settled 2 threads, Ctrl+Z to undo
8760ms live(polite): Undid settle of 2 threads                  <- grouped undo
56199ms KEY: snooze Add dark mode (sidebar Snooze > In 1 hour), then ctrl+z
57868ms focus: menuitem
58201ms live(polite): Snoozed 1 thread, Ctrl+Z to undo
61067ms live(polite): Undid snooze of 1 thread                  <- snooze undo
88048ms KEY: archive Fix login bug (context menu > Archive thread), then ctrl+z
89690ms focus: Message New thread        (archiving the open thread navigates to a new draft)
89940ms live(polite): Archived 1 thread, Ctrl+Z to undo
         (ctrl+z arrived after the 5 s undo window because of tool latency: nothing to undo, silent; same as main)
140214ms KEY: archive Add dark mode (context menu > Archive thread), then ctrl+z immediately
141782ms live(polite): Archived 1 thread, Ctrl+Z to undo
143098ms live(polite): Undid archive of 1 thread                <- archive undo
170976ms KEY: discard draft "Draft about caching" (sidebar Discard draft button), then ctrl+z
171228ms live(polite): Discarded 1 draft, Ctrl+Z to undo
172535ms live(polite): Undid discard of 1 draft                 <- discard undo
Partial-failure / failed undo: covered by unit test "does not announce an undo that failed" (no live reproduction: needs a server-side failure).