feat(#2102): skip startup rebuild for stopped/unchanged containers

hive-c0re/src/rebuild_queue.rs

@@ -1034,11 +1034,33 @@ async fn rebuild_for_entry(
 /// Uses the cold-start fallback (stop + kill + start retry) so the
 /// deferred start-after-rebuild keeps the same activation-error recovery
 /// it had when it ran inline on the build lane.
+///
+/// If the hyperhive flake rev has changed since the container was last built
+/// (i.e. the rev marker is stale or missing), the start is upgraded to a full
+/// rebuild so the container runs current nix derivations. This is the
+/// "deferred stopped container" path from `auto_update::run`.
 async fn run_start(
     coord: &std::sync::Arc<crate::coordinator::Coordinator>,
     entry: &QueueEntry,
 ) -> anyhow::Result<()> {
     let name = &entry.agent;
+    // Upgrade to rebuild+start if the rev marker is stale.
+    let current_rev = crate::auto_update::current_flake_rev(&coord.hyperhive_flake);
+    if let Some(ref rev) = current_rev {
+        let stored = std::fs::read_to_string(crate::auto_update::rev_marker_path(name)).ok();
+        if stored.as_deref() != Some(rev.as_str()) {
+            tracing::info!(%name, "start: rev stale — upgrading to rebuild+start");
+            return crate::auto_update::rebuild_agent(
+                coord,
+                name,
+                rev,
+                Some(entry.id),
+                true,
+                Some(entry.source),
+            )
+            .await;
+        }
+    }
     let _guard = coord.transient_guard(name, crate::coordinator::TransientKind::Starting);
     coord.set_queue_step(Some(entry.id), "nixos-container start");
     crate::lifecycle::start_with_fallback(name).await?;