jobq: key transient tombstones per pill, not per agent

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.

hive-c0re/src/dashboard_events.rs

@@ -157,7 +157,18 @@ pub enum DashboardEvent {
     },
     /// The matching lifecycle action resolved (success or failure).
     /// Clients drop the spinner row.
-    TransientCleared { seq: u64, name: String },
+    ///
+    /// `transient_kind` matches the `TransientSet` that opened this pill, and is
+    /// what makes the pair addressable: an agent can hold **several** pills at
+    /// once (the transient set tests status alone, so a lease-exempt `Prebuild`
+    /// and a lease-holding `StopForUpdate` are both live). Without it a client
+    /// holding two open pills for one agent cannot tell which one cleared, and
+    /// has to drop both or guess.
+    TransientCleared {
+        seq: u64,
+        name: String,
+        transient_kind: String,
+    },
     /// One container row changed — new container appeared (post-spawn
     /// finalise), an existing one flipped `running` / `needs_update` /
     /// `sha`, etc. Clients upsert by `container.name`. Payload carries
@@ -392,6 +403,7 @@ mod tests {
             DashboardEvent::TransientCleared {
                 seq: 1,
                 name: "x".into(),
+                transient_kind: "rebuilding".into(),
             },
             DashboardEvent::ContainerRemoved {
                 seq: 1,