TODO 2.9 recorded a retention policy that warned about low disk while freeing
0.0 GB twice in a row, because it governed artifacts, logs and IP leases -- 52
KB in total on this host -- while 195 G of backups sat outside its reach.
Adding an unbounded directory of ~645 MB entries, one per Cargo.lock change,
without extending retention in the same change would repeat that at a larger
scale.
The window is the tighter of the global retention and the cache's own, so the
aggressive low-disk mode reaches the cache rather than stopping at the light
directories.
Sizes are read before deleting, not after. Summing st_size over files that have
already been unlinked yields 0 -- which is exactly how a policy ends up
reporting that it freed nothing while doing real work. A test asserts the
reported figure.
Simone
15b1676375