Re: [GSoC PATCH v2 0/7] repack: add --drop-filtered to reclaim space in partial clones

Siddharth Shrimali [off-list ref] writes:

So they are a convenience to avoid pointless re-fetching, not a
correctness measure.
I am happy to drop them or keep them clearly documented as just that,
whichever the list prefers.

Doesn't it suggest that the "cull anything refetchable" feature can
gain a bit more smart?  Given an object you know you fetched from a
promisor remote, are there cheap ways to determine how long you had
it in your repository?  "This large blob can be refetched if we
wanted to, but we downloaded it just 20 minutes ago, so let's not
cull it just yet", or something like that, perhaps?