The repro proved the launcher holds a daemon it can see is occupied. The protection
that now matters most is the one for a daemon it cannot see at all, and nothing
asserted it. Adds the unknown-hold to the static assertions: that it exists, that it
excludes 'rejected' and a proven-dead endpoint, and that every killStaleDaemon call
site in the file is downstream of it.
Verified by mutation — dropping either exclusion fails the assertion.