hive-c0re: replace the agents_crashing banner with a crash-watcher log line + grafana alert

docs/agent-lifecycle/config-changes.md

@@ -359,42 +359,42 @@ the system prompt template.
 
 ## Helper events
 
-`Coordinator::notify_agent(agent, &HelperEvent)` pushes the event into
-the agent's inbox, and the harness delivers it as a regular `system`
-inbox message so it drives a normal claude turn. A "FYI, check when
-convenient" event doesn't need a message — hive-c0re publishes those as
-swarm lifecycle notices instead (`swarm_notices::notify`). Variants
-(`hive_sh4re::manager::HelperEvent`):
+`hive_sh4re::manager::HelperEvent` is the wire type for an event urgent
+enough to drive an immediate claude turn (delivered as a regular
+`system` inbox message, same `recv` path as any other message). It
+currently has one variant, `NeedsUpdate { agent }` (sub-agent's
+recorded flake rev is stale, operator rebuilds from the dashboard) —
+and nothing in the tree constructs it; the push path
+(`Coordinator::notify_agent`) was removed once its last caller
+(`notify_manager`, used only for the crash event below) went away.
+`HelperEvent` is kept as the type for whatever comes along that
+genuinely needs to interrupt an agent's turn loop, not because
+anything live uses it today.
 
-- `ContainerCrash { agent, note }` — `crash_watch`: a previously-
-  running container went away with no operator-initiated transient
-  state (Stopping / Restarting / Destroying / Rebuilding) AND nothing
-  cleared that transient in the last 30s (`RECENT_TRANSIENT_GRACE`
-  tombstone, three `POLL_INTERVAL`s — closes the race where a
-  lifecycle op finishes between two crash-watch polls and the
-  container shows briefly as "stopped without transient" before
-  the next start). When `systemctl is-active` fails or runs past its
-  10s bound on a poll, the container keeps its previous state for that
-  poll, so an unreadable unit never counts as a crash.
-  The root agent escalates to the operator, who starts it again from
-  the dashboard.
-- `NeedsUpdate { agent }` — sub-agent's recorded flake rev is
-  stale. The operator rebuilds it from the dashboard.
+**A previously-running container crashing** used to be exactly that
+case (`ContainerCrash`, routed to the root agent via
+`Coordinator::notify_manager`) — it no longer drives any agent turn at
+all. `crash_watch` now only `tracing::warn!`s `"container crash
+detected"`; a swarm-level grafana alert matches that log line directly
+and pages the operator, with no agent (and no per-hive dashboard
+banner) in the loop. See
+[`docs/scheduler/observability.md`](../scheduler/observability.md#container-crash-alerting-hive-c0re).
 
 The remaining lower-urgency lifecycle notices — `Rebuilt`, `Killed`,
 `Destroyed`, `NeedsLogin`, `LoggedIn` — are "FYI, check
 when convenient" events with no reason to drive an immediate turn, so
-they go out via `swarm_notices::notify` (see above) instead
+they go out via `swarm_notices::notify` instead
 of a `HelperEvent`: `subsystem = "core"`, `key = "<event>:<agent>"`,
 and a single free-text `summary` (`rebuilt_todo_summary` renders
 `Rebuilt`'s `ok`/`note`/`sha`/`tag` fields into that string).
 
-To add a new lifecycle notice: if it needs to drive an immediate turn
-(something genuinely urgent, like `ContainerCrash`), add a
-`HelperEvent` variant + call sites + update `prompts/system.md`'s
-message-event list. If it's "FYI, check when convenient," call
-`swarm_notices::notify` instead — no new wire type
-needed.
+To add a new lifecycle notice: if it's "FYI, check when convenient,"
+call `swarm_notices::notify` — no new wire type needed. If it needs to
+drive an immediate turn, decide first whether it actually needs an
+*agent* in the loop at all (the crash case above didn't, once a
+swarm-level alert could carry the same signal) — only reach for a new
+`HelperEvent` variant + `notify_agent`-equivalent call site +
+`prompts/system.md` update when the answer is yes.
 
 ## Autoupdate on startup