unconscious: event-driven loop via tokio::select!

Replace yield_now() polling with proper event-driven wakeups:
- Add wake: Arc<Notify> to Unconscious struct
- Spawned agents call wake.notify_one() on completion
- Loop uses select! on: unc_rx.changed(), wake.notified(), health timer

Eliminates spinning (was 27.9M iterations per interval).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/mind/unconscious.rs

@@ -71,6 +71,8 @@ pub struct Unconscious {
     max_concurrent: usize,
     pub graph_health: Option<crate::subconscious::daemon::GraphHealth>,
     last_health_check: Option<Instant>,
+    /// Notified when agent state changes (finished, toggled)
+    pub wake: std::sync::Arc<tokio::sync::Notify>,
 }
 
 impl Unconscious {
@@ -117,6 +119,7 @@ impl Unconscious {
             agents, max_concurrent,
             graph_health: None,
             last_health_check: None,
+            wake: std::sync::Arc::new(tokio::sync::Notify::new()),
         }
     }
 
@@ -130,11 +133,13 @@ impl Unconscious {
         if new_state && !self.agents[idx].is_running() && self.agents[idx].auto.is_some() {
             let agent_name = self.agents[idx].name.clone();
             let auto = self.agents[idx].auto.take().unwrap();
-            match prepare_spawn(&agent_name, auto).await {
+            let wake = self.wake.clone();
+            match prepare_spawn(&agent_name, auto, wake).await {
                 Ok(result) => self.complete_spawn(idx, result),
                 Err(auto) => self.abort_spawn(idx, auto),
             }
         }
+        self.wake.notify_one(); // wake loop to consider new state
         Some(new_state)
     }
 
@@ -245,7 +250,7 @@ pub struct SpawnResult {
 /// Called outside the Unconscious lock.
 /// On success, auto is consumed (moved into spawned task).
 /// On failure, auto is returned so it can be restored.
-pub async fn prepare_spawn(name: &str, mut auto: AutoAgent) -> Result<SpawnResult, AutoAgent> {
+pub async fn prepare_spawn(name: &str, mut auto: AutoAgent, wake: std::sync::Arc<tokio::sync::Notify>) -> Result<SpawnResult, AutoAgent> {
     dbglog!("[unconscious] spawning {}", name);
 
     let def = match defs::get_def(name) {
@@ -312,6 +317,7 @@ pub async fn prepare_spawn(name: &str, mut auto: AutoAgent) -> Result<SpawnResul
         let stats = crate::agent::oneshot::save_agent_log(&auto.name, &agent_clone).await;
         auto.update_stats(stats);
         auto.steps = orig_steps;
+        wake.notify_one(); // wake the loop to reap and maybe spawn more
         (auto, result)
     });
 
@@ -323,8 +329,9 @@ impl Unconscious {
     pub async fn trigger(&mut self) {
         self.reap_finished();
         let to_spawn = self.select_to_spawn();
+        let wake = self.wake.clone();
         for (idx, name, auto) in to_spawn {
-            match prepare_spawn(&name, auto).await {
+            match prepare_spawn(&name, auto, wake.clone()).await {
                 Ok(result) => self.complete_spawn(idx, result),
                 Err(auto) => self.abort_spawn(idx, auto),
             }