isLive treated any RuntimeException from the liveness probe as "the lead is
gone", which forgetDelegation then acted on destructively and permanently.
That made a transient herdr hiccup (socket blip, decode error) on a perfectly
live lead indistinguishable from the lead actually being dead — the same
one-bad-reading mistake #359 shipped a guard against for lead-tab liveness.
Narrow isLive to match AgentControl.agentCall's own rule: only an affirmative
HerdrException("agent_not_found") counts as gone. Every other failure is
treated as still live and the binding is left alone.
Adds aTransientLivenessFailureMustNotForgetABindingToAStillLiveLead, which
fails with the bare RuntimeException catch and passes with the narrowed one.
Dai Ha
d6ef0c8013