@pettter It's built in to the PuSH/WebSub protocol that subscriptions all have leases (lease time dictated by the publisher/hub). If that time is coming near, the subscriber should ping the hub about renewing.

If the PuSH/WebSub hub stops delivering despite having an active subscription it's breaking the protocol (default lease time tends to be ~1 month, so it's not really a problem just keeping on delivering despite suspicious that something is wrong). This was probably the reason why pushes stopped coming, since Mastodon is so eager to be ultramegasuperefficient at the cost of hickups becoming disasters.

But I think @Gargron has fixed (or will fix) this by reverting the "Oh I'll assume the remote side is dead because it returned a 4xx status" antifeature.