diff --git a/docs/agent-lifecycle/config-changes.md b/docs/agent-lifecycle/config-changes.md
index ea41dd98..3ef05de4 100644
--- a/docs/agent-lifecycle/config-changes.md
+++ b/docs/agent-lifecycle/config-changes.md
@@ -44,10 +44,12 @@ No MCP tool exists for config changes: opening the PR IS the request.
    deploy subject. With no such hive, or more than one, it deploys
    nothing and logs a warning naming them.
 5. If the hive's `applied/main` already is that commit, it does nothing.
-   Otherwise it fetches the config repo's `main`, requires the commit to
-   descend from `applied/main`, fast-forwards `applied/main` to it, and
-   queues a rebuild. A failure before the rebuild (the fetch, or a commit
-   that doesn't descend) deploys nothing and logs `swarm events: rev not
+   Otherwise it fetches the config repo's `main`. A commit that
+   `applied/main` already contains is a no-op too: requests for two merges
+   can arrive in either order. A commit that descends from `applied/main`
+   is fast-forwarded to and a rebuild queued. A failure before the rebuild
+   (the fetch, or a commit that has diverged from `applied/main`) deploys
+   nothing and logs `swarm events: rev not
    applied; nothing queued` at error, which fires the Grafana alert
    `config rev refused`. An agent with no container on that hive yet ignores
    the commit; its first deploy builds what it seeds.
diff --git a/hive-c0re/src/actions.rs b/hive-c0re/src/actions.rs
index cc3c074e..841e123e 100644
--- a/hive-c0re/src/actions.rs
+++ b/hive-c0re/src/actions.rs
@@ -30,6 +30,11 @@ pub(crate) enum RevAdvance {
     AlreadyApplied,
     /// `applied/main` was fast-forwarded to the rev.
     Advanced,
+    /// The rev is an ancestor of `applied/main`, so a later commit already
+    /// carries it and there is nothing to deploy. Deploy requests are not
+    /// ordered: two merges' requests can arrive in either order, and a
+    /// meta-update cascade fast-forwards `main` to the forge's on its own.
+    Superseded,
 }
 
 /// Fast-forward `agent`'s `applied/main` to `rev`, a commit the swarm asks
@@ -40,8 +45,8 @@ pub(crate) enum RevAdvance {
 ///
 /// # Errors
 ///
-/// Returns an error if the forge fetch fails, if `rev` does not descend from
-/// `applied/main`, or if `main` moved during the fast-forward. `main` does not
+/// Returns an error if the forge fetch fails, if `rev` has diverged from
+/// `applied/main` (neither descendant nor ancestor), or if `main` moved during the fast-forward. `main` does not
 /// move in any of these.
 pub(crate) async fn advance_applied_to_rev(agent: &str, rev: &str) -> Result<RevAdvance> {
     advance_applied_main(
@@ -75,6 +80,12 @@ async fn advance_applied_main<T>(
         return Ok(RevAdvance::AlreadyApplied);
     }
     if !descends {
+        let contained = lifecycle::git_is_ancestor(applied_dir, rev, &main)
+            .await
+            .map_err(|e| anyhow::anyhow!("ancestry check {rev}..{main}: {e:#}"))?;
+        if contained {
+            return Ok(RevAdvance::Superseded);
+        }
         bail!(
             "{rev} does not descend from applied/main ({main}); fast-forwarding to it would \
              discard commits"
@@ -211,6 +222,14 @@ mod tests {
         assert_eq!(main_of(&dir).await, b);
     }
 
+    #[tokio::test]
+    async fn an_ancestor_of_main_is_superseded_not_refused() {
+        let (dir, [a, b, _]) = repo().await;
+        let outcome = advance_applied_main(dir.path(), &a, async { anyhow::Ok(()) }).await;
+        assert_eq!(outcome.expect("no-op"), RevAdvance::Superseded);
+        assert_eq!(main_of(&dir).await, b);
+    }
+
     #[tokio::test]
     async fn a_descendant_rev_fast_forwards_main() {
         let (dir, [a, b, _]) = repo().await;
diff --git a/hive-c0re/src/swarm_status.rs b/hive-c0re/src/swarm_status.rs
index dee3ef13..67f7ac50 100644
--- a/hive-c0re/src/swarm_status.rs
+++ b/hive-c0re/src/swarm_status.rs
@@ -328,6 +328,10 @@ async fn apply_rev(agent: &str, rev: &str) -> bool {
             tracing::info!(%agent, %rev, "swarm events: deploy requested for the applied rev; nothing queued");
             false
         }
+        Ok(crate::actions::RevAdvance::Superseded) => {
+            tracing::info!(%agent, %rev, "swarm events: deploy requested for a rev applied/main already contains; nothing queued");
+            false
+        }
         Err(e) => {
             tracing::error!(%agent, %rev, error = %format!("{e:#}"), "swarm events: rev not applied; nothing queued");
             false