remove the needs_update system event: nothing emits it

Refs #5948

hive-agent/prompts/system.md

@@ -22,10 +22,7 @@ You are built from the `{archetype}` archetype and have no config repo of your o
 
 Operator boundary: starting, stopping and rebuilding containers is the operator's — ask them when any agent needs one. _Creating_ a new agent is not something you can do from here — ask the operator, who creates agents at swarm level. The operator only signs off on changes; you run the day-to-day.
 
-Messages from sender `system` are hyperhive helper events (JSON body, `event` field discriminates): `container_crash`, `needs_update`. Use these to react to lifecycle changes:
-
-- `needs_update` — agent's flake rev is stale. Ask the operator to rebuild it.
-- `container_crash` — ask the operator to start it again; if it keeps crashing, say so with what you saw.
+Messages from sender `system` are plain-text notices from hive-c0re, not peer messages. Two kinds today: a `/knowledge updated` broadcast (read the changed files in `/knowledge`), and the wake message for a graceful stop (check `/agents/<you>/state/` for your notes). A container crash sends you nothing; the operator is alerted separately.
 
 Lifecycle notices that don't need an immediate turn — a new agent spawned, a container rebuilt/killed/destroyed, or its login state changing — surface as todos instead of messages now. Call `get_loose_ends` to see them.
 

hive-agent/src/main.rs

@@ -107,7 +107,7 @@ use crate::turn_stats::TurnStats;
 use anyhow::Result;
 use clap::Parser;
 use hive_core_agent_sock::{Request, Response};
-use hive_sh4re::manager::{HelperEvent, SYSTEM_SENDER};
+use hive_sh4re::manager::SYSTEM_SENDER;
 use hive_sock_client::Retry;
 
 #[derive(Parser)]
@@ -134,21 +134,12 @@ async fn main() -> Result<()> {
 // ---------- shared turn helpers ----------
 
 /// Surface a `SYSTEM_SENDER` message in the live event bus + tracing
-/// log. Both agents and the manager receive `HelperEvent` notifications
-/// (just `NeedsUpdate`, now that a container crash is a log line instead
-/// of a `ContainerCrash` event); the parse and log path is
-/// identical. Quiet no-op when `from` isn't
-/// `SYSTEM_SENDER`.
+/// log. Quiet no-op when `from` isn't `SYSTEM_SENDER`.
 fn log_system_event(bus: &Bus, from: &str, body: &str) {
     if from != SYSTEM_SENDER {
         return;
     }
-    let parsed = serde_json::from_str::<HelperEvent>(body).ok();
-    if let Some(event) = &parsed {
-        tracing::info!(?event, "helper event");
-    } else {
-        tracing::info!(%from, %body, "system message");
-    }
+    tracing::info!(%from, %body, "system message");
     bus.emit(LiveEvent::Note {
         text: format!("[system] {body}"),
     });