diff --git a/hive-c0re/src/forge/config_pr_poll.rs b/hive-c0re/src/forge/config_pr_poll.rs
index b74b587a..ba233b44 100644
--- a/hive-c0re/src/forge/config_pr_poll.rs
+++ b/hive-c0re/src/forge/config_pr_poll.rs
@@ -93,32 +93,12 @@ pub async fn poll_open_config_prs(core_token: &str, coord: &Arc<Coordinator>) ->
             };
             open_prs.insert((agent.to_owned(), pr_number));
 
-            // Skip if a pending approval already exists for this PR.
-            match coord
-                .approvals
-                .has_pending_merge_config_pr(agent, pr_number)
-            {
-                Ok(true) => {
-                    tracing::debug!(
-                        %agent, %pr_number,
-                        "config-pr poll: approval already pending, skipping"
-                    );
-                    continue;
-                }
-                Ok(false) => {}
-                Err(e) => {
-                    tracing::warn!(
-                        %agent, %pr_number, error = ?e,
-                        "config-pr poll: DB check failed, skipping"
-                    );
-                    continue;
-                }
-            }
-
-            tracing::info!(
-                %agent, %pr_number,
-                "config-pr poll: queuing missed MergeConfigPr approval"
-            );
+            // `submit_merge_config_pr` is idempotent + PR-drift aware: it
+            // no-ops when an approval pinned to this PR's *current* head is
+            // already pending, and cancels+re-queues when the head has drifted.
+            // So the poll can call it unconditionally — it backstops both a
+            // missed `opened` webhook (no approval yet) and a missed
+            // `synchronize` (stale approval whose head moved).
             let description = format!("PR #{pr_number} on {CONFIG_ORG}/{agent} (poll fallback)");
             if let Err(e) = crate::socket_server::submit_merge_config_pr(
                 coord,
@@ -131,7 +111,7 @@ pub async fn poll_open_config_prs(core_token: &str, coord: &Arc<Coordinator>) ->
             {
                 tracing::warn!(
                     %agent, %pr_number, error = ?e,
-                    "config-pr poll: failed to queue MergeConfigPr approval"
+                    "config-pr poll: failed to reconcile MergeConfigPr approval"
                 );
             }
         }
diff --git a/hive-c0re/src/socket_server/config_approvals.rs b/hive-c0re/src/socket_server/config_approvals.rs
index 37bdc2e7..6a3ea8f3 100644
--- a/hive-c0re/src/socket_server/config_approvals.rs
+++ b/hive-c0re/src/socket_server/config_approvals.rs
@@ -157,6 +157,31 @@ pub(crate) async fn submit_merge_config_pr(
     let sha = crate::forge::pr_head_sha(&repo, pr_number)
         .await
         .map_err(|e| anyhow::anyhow!("fetch PR head sha for {agent} PR #{pr_number}: {e}"))?;
+    // Both the webhook (`synchronize`) and the poll fallback call this on
+    // every PR update. If an approval for this PR is already pending, reconcile
+    // it against the live head sha rather than blindly queuing another:
+    //   - same sha → the PR hasn't moved, so this is a duplicate signal — no-op.
+    //   - drifted sha → the reviewed head is stale. Don't mutate the
+    //     pending row in place (that races a concurrent approve); cancel it and
+    //     fall through to queue a FRESH approval pinned to the new head.
+    if let Some((old_id, old_sha)) = coord.approvals.pending_merge_config_pr(agent, pr_number)? {
+        if old_sha.as_deref() == Some(sha.as_str()) {
+            return Ok(old_id);
+        }
+        let cancelled = coord
+            .approvals
+            .mark_cancelled(old_id, "config PR updated — superseded by a fresh approval")
+            .map_err(|e| anyhow::anyhow!("cancel superseded merge_config_pr approval: {e:#}"))?;
+        coord.emit_approval_resolved(crate::coordinator::ApprovalResolved {
+            id: old_id,
+            agent,
+            approval_kind: "merge_config_pr",
+            sha_short: old_sha.map(|s| s[..s.len().min(12)].to_owned()),
+            status: "cancelled",
+            note: Some("PR head moved; superseded by a fresh approval".to_owned()),
+            description: cancelled.description,
+        });
+    }
     let id = coord
         .approvals
         .submit_kind(
diff --git a/hive-c0re/src/stores/approvals.rs b/hive-c0re/src/stores/approvals.rs
index 1f511e35..da67397a 100644
--- a/hive-c0re/src/stores/approvals.rs
+++ b/hive-c0re/src/stores/approvals.rs
@@ -136,19 +136,29 @@ impl Approvals {
         Ok(())
     }
 
-    /// Return `true` when there is already a `pending` `merge_config_pr`
-    /// approval for `(agent, pr_number)`. Used by the polling fallback to
-    /// skip re-submitting approvals that were already queued by the webhook.
-    pub fn has_pending_merge_config_pr(&self, agent: &str, pr_number: u64) -> Result<bool> {
+    /// Return the `(id, fetched_sha)` of the pending `merge_config_pr`
+    /// approval for `(agent, pr_number)`, if one exists. Drives
+    /// `submit_merge_config_pr`'s idempotency + PR-drift handling: same
+    /// `fetched_sha` → no new request (the webhook + poll both call submit,
+    /// so re-submits of an unchanged PR must be no-ops); a drifted head →
+    /// cancel this stale row and queue a fresh approval.
+    pub fn pending_merge_config_pr(
+        &self,
+        agent: &str,
+        pr_number: u64,
+    ) -> Result<Option<(i64, Option<String>)>> {
         let conn = self.conn.lock().unwrap();
-        let count: i64 = conn.query_row(
-            "SELECT COUNT(*) FROM approvals \
-              WHERE agent = ?1 AND kind = 'merge_config_pr' \
-                AND commit_ref = ?2 AND status = 'pending'",
-            params![agent, pr_number.to_string()],
-            |row| row.get(0),
-        )?;
-        Ok(count > 0)
+        let row = conn
+            .query_row(
+                "SELECT id, fetched_sha FROM approvals \
+                  WHERE agent = ?1 AND kind = 'merge_config_pr' \
+                    AND commit_ref = ?2 AND status = 'pending' \
+                  ORDER BY id DESC LIMIT 1",
+                params![agent, pr_number.to_string()],
+                |row| Ok((row.get(0)?, row.get(1)?)),
+            )
+            .optional()?;
+        Ok(row)
     }
 
     /// Last `limit` resolved approvals (approved / denied / failed),