After: fix/issue-23653 at 90d4467b8a, same web dev server (HMR, page reloaded), same seeded threads, same MutationObserver/focusin logger.
3188ms KEY: ctrl+shift+s settle (Add dark mode)
5089ms focus: Message Write release notes
5506ms live(polite): Settled 1 thread, Ctrl+Z to undo
7456ms KEY: ctrl+z undo
8208ms live(polite): Undid settle of 1 thread          <- new
14450ms KEY: ctrl+shift+p pin (Write release notes)
16501ms live(polite): Pinned 1 thread                  <- new
22782ms KEY: ctrl+shift+p unpin (Write release notes)
24819ms live(polite): Unpinned 1 thread, Ctrl+Z to undo
30993ms KEY: ctrl+z (6 s later: the 5 s undo window had expired, so nothing to undo; correctly silent)
(ctrl+shift+p pin -> 54488ms live(polite): Pinned 1 thread)
57438ms KEY: ctrl+shift+p unpin, then ctrl+z within the window
57956ms live(polite): Unpinned 1 thread, Ctrl+Z to undo
59481ms live(polite): Undid unpin of 1 thread           <- new; no extra "Pinned 1 thread" from the re-pin