Static Cache Soft purge

[timkelty]

Cloudflare is supposed to finally be getting a "soft purge" feature, which we want to use when available.

Craft Cloud already support async stale-while-revalidate, so when things naturally expire, clients should never see MISSes.
The other side to that is manual purge, which Craft sites take more advantage of via tag purging.

With soft purge, sites could effectively serve static cache HITs 100% of the time, without any explicit warming.

[jamesmacwhite]

10/10 HIT me again.

If implemented this is huge!

[timkelty]

Amen!

We'd love to implement this ourselves, but the solution is pretty complex, and knowing that it is around the corner, we've decided to wait.

FWIW, "async stale-while-revalidate" is a recent Cloudflare change that was rolled out in the past month or so on our zone.