I think there are two components to this:

First, figuring out what a lease is connected to. Leases have an ownerPHID since D1454, but it may not be getting populated very consistently. It should be consistently populated. I think this covers the general "why does this thing exist?" need.

In the second case, I plan to make Drydock work like the worker queue does: leases have a time limit, and expire automatically if not extended.

I'd broadly expect a Harbormaster build which needs a lease to work like this when it starts up:

1. Check if it already has a valid lease stored somewhere.
2. If not, build one, then cache it.

This gets us the right behavior on all sorts of restarts / failures / etc. There's no easy way for workers to be internally stateful right now but that's easy to add if it doesn't make sense to do it as part of build targets.

That is, if a lease owner truly vanishes, the cleanup mechanism is that the lease duration expires and it gets GC'd eventually. Then we never have to reach back up into applications to see if they still need leases, which is a question they probably can't easily answer most of the time anyway (specifically, I believe the answer is always "yes" if they haven't explicitly released the lease and are implemented correctly/consistently).

I'll leave this open until T9123 is closer to resolving and there's some implemented behavior here, but I don't think this needs anything new per se.