Deletes `TransientState`, adds `transient_kind` to `TransientCleared`, and
fixes a crash misreport — three changes over the same functions.
`TransientState` was `RunningTransient` with `agent` dropped and
`takes_container_down` renamed; that rename was the only thing it did, and
its three consumers each read a disjoint subset. `transient_snapshot` now
returns `RunningTransient` directly.
`recent_transient` was keyed by agent alone and overwritten on each clear.
An agent can clear several pills in one grace window, so a `Prebuild`
(`takes_container_down = false`) landing after a `StopForUpdate` (`true`)
left the tombstone reading `false` and the crash watcher reported a
deliberate stop as a container crash. Keyed by `(agent, label)` now, with
`recent_transient_within` folding back per agent by OR — the same question
`crash_watch` asks of the active set.
`TransientCleared` gains the label for the same reason: a client holding
two open pills for one agent could not tell which one a clear referred to.
The out-of-band suppression guard has no node and so no label; it uses
`NO_NODE_LABEL`, angle-bracketed to stay out of the `NodeKind::as_str`
namespace.
7ef0e8c788