This boot's id, stamped into the HostInstanceID of the bridge rows it creates.
The prefix every boot of this instance stamps and no other instance's id starts with. The reconcile reads the
open bridge rows under it (a SQL LIKE), then asks IHostInstanceIdentity.IsPriorBoot about each one.
Whether a HostInstanceID was stamped by another boot of this instance, a process that has ended. False for
this boot's id, for any other instance's, and for null. The reconcile closes a row only when this is true, so
the check must be exact: a SQL LIKE reads a _ in a host name as any character.
A bridge row's HostInstanceID.
The IHostInstanceIdentity the engine uses until the host injects one: this process alone, on this host. Its id is
hostname:pid-<pid>:<pid>:<bootId>, the shape MJServer gives a process that serves no port, so DefaultHostInstanceIdentity.IsPriorBoot matches only an earlier process that had this pid on this host, which has ended. It never matches another live process's bridges. A host whose instance outlives a restart (MJServer: a host and a port) injects its own identity, so that its reconcile closes what an earlier boot left.