day    source  exit  alerts  state count  state observed_at        age of the value
   0      rows     0       0            3  2026-08-27T20:07:49  0 day(s) old
   1      rows     0       3            4  2026-08-28T20:07:49  0 day(s) old
   2     empty     0       0            4  2026-08-28T20:07:49  1 day(s) old
   3     empty     0       0            4  2026-08-28T20:07:49  2 day(s) old
   4     empty     0       0            4  2026-08-28T20:07:49  3 day(s) old

[ok] every run exited 0
[ok] no alert fired on any run after the source went empty
[ok] the last state file is 3 day(s) older than the run that wrote it
[ok] and it is still well formed, correctly typed and validated by the subject on the way in

The watcher checks the shape of the value and never its age. That is the whole bug,
and it is one `if` away from being fixed, which is what makes it worth measuring rather
than arguing about.