When topping up the summarised counts with push actions that have not been
rotated yet, the main timeline branch incremented `counts`, the variable left
over from the loop that read the summary rows, rather than the main timeline's
own counts. Whichever thread the summary query returned last would absorb the
main timeline's un-rotated notifications.
The room total is unaffected, and the unique index on `event_push_summary`
means real thread IDs (event IDs, starting with `$`) sort before `main`, so in
practice `main` is returned last and the bug is masked. The test pins it with a
synthetic summary row whose thread ID sorts after `main`.
Quentin Gliech
f6241d3ed8