diff --git a/server/src/agents/lifecycle.rs b/server/src/agents/lifecycle.rs
index 49296c7a..f8b618bf 100644
--- a/server/src/agents/lifecycle.rs
+++ b/server/src/agents/lifecycle.rs
@@ -179,7 +179,7 @@ pub fn move_story_to_merge(project_root: &Path, story_id: &str) -> Result<(), St
         story_id,
         &["2_current", "3_qa"],
         "4_merge",
-        &[],
+        &["5_done", "6_archived"],
         false,
         &["retry_count", "blocked"],
     )
@@ -195,7 +195,7 @@ pub fn move_story_to_qa(project_root: &Path, story_id: &str) -> Result<(), Strin
         story_id,
         &["2_current"],
         "3_qa",
-        &[],
+        &["5_done", "6_archived"],
         false,
         &["retry_count", "blocked"],
     )
diff --git a/server/src/agents/pool/pipeline/advance.rs b/server/src/agents/pool/pipeline/advance.rs
index 80f4d3cd..bc09a183 100644
--- a/server/src/agents/pool/pipeline/advance.rs
+++ b/server/src/agents/pool/pipeline/advance.rs
@@ -231,6 +231,23 @@ impl AgentPool {
                 }
             }
             PipelineStage::Mergemaster => {
+                // Bug 529: Guard against stale mergemaster advances.  If the story
+                // has already reached done or archived (e.g. a previous mergemaster
+                // succeeded), this advance is a zombie — skip it entirely to avoid
+                // phantom notifications and redundant post-merge test runs.
+                if let Ok(Some(typed_item)) = crate::pipeline_state::read_typed(story_id) {
+                    let current_dir = typed_item.stage.dir_name();
+                    if current_dir == "5_done" || current_dir == "6_archived" {
+                        slog!(
+                            "[pipeline] Skipping stale mergemaster advance for '{story_id}': \
+                             story is already in work/{current_dir}/"
+                        );
+                        // Skip pipeline advancement — do not run post-merge tests,
+                        // do not emit notifications, do not restart agents.
+                        return;
+                    }
+                }
+
                 // Block advancement if the mergemaster explicitly reported a failure.
                 // The server-owned gate check runs in the feature-branch worktree (not
                 // master), so `gates_passed=true` is misleading when no code was merged.
@@ -885,4 +902,88 @@ stage = "qa"
                 .collect::<Vec<_>>()
         );
     }
+
+    // ── bug 529: stale mergemaster advance for a done story is a no-op ──
+
+    /// Regression test for bug 529: when a stale mergemaster advance fires
+    /// after the story has already reached 5_done, the advance must be a
+    /// no-op — no post-merge tests, no notifications, no agent restarts.
+    #[tokio::test]
+    async fn stale_mergemaster_advance_for_done_story_is_noop() {
+        use std::fs;
+        use std::process::Command;
+
+        // Initialise CRDT so read_typed works.
+        crate::crdt_state::init_for_test();
+        crate::db::ensure_content_store();
+
+        let tmp = tempfile::tempdir().unwrap();
+        let root = tmp.path();
+
+        // Init a git repo so post-merge tests would pass if they ran.
+        Command::new("git").args(["init"]).current_dir(root).output().unwrap();
+        Command::new("git").args(["config", "user.email", "test@test.com"]).current_dir(root).output().unwrap();
+        Command::new("git").args(["config", "user.name", "Test"]).current_dir(root).output().unwrap();
+        Command::new("git").args(["commit", "--allow-empty", "-m", "init"]).current_dir(root).output().unwrap();
+
+        // Set up pipeline dirs.
+        fs::create_dir_all(root.join(".huskies/work/5_done")).unwrap();
+
+        // Seed the story in 5_done via the DB, which also writes to the CRDT.
+        let story_id = "9929_story_zombie_merge";
+        let content = "---\nname: Zombie Merge Test\n---\n";
+        crate::db::write_content(story_id, content);
+        crate::db::write_item_with_content(story_id, "5_done", content);
+
+        let pool = AgentPool::new_test(3001);
+        let mut rx = pool.watcher_tx.subscribe();
+
+        // Simulate a stale mergemaster advance firing for the already-done story.
+        pool.run_pipeline_advance(
+            story_id,
+            "mergemaster",
+            CompletionReport {
+                summary: "stale advance".to_string(),
+                gates_passed: true,
+                gate_output: String::new(),
+            },
+            Some(root.to_path_buf()),
+            None,
+            false,
+        )
+        .await;
+
+        // No agents should have been started.
+        let agents = pool.agents.lock().unwrap();
+        assert!(
+            agents.is_empty(),
+            "No agents should be started for a stale advance on a done story. \
+             Pool: {:?}",
+            agents.keys().collect::<Vec<_>>()
+        );
+        drop(agents);
+
+        // No StoryBlocked or other events should have been emitted.
+        let mut got_event = false;
+        while let Ok(evt) = rx.try_recv() {
+            // AgentStateChanged from auto_assign is acceptable only if the
+            // advance didn't short-circuit.  Since we return early, no events.
+            if matches!(evt, WatcherEvent::StoryBlocked { .. }) {
+                got_event = true;
+            }
+        }
+        assert!(
+            !got_event,
+            "No StoryBlocked event should be emitted for a stale advance"
+        );
+
+        // The story should still be in 5_done (not moved elsewhere).
+        if let Ok(Some(item)) = crate::pipeline_state::read_typed(story_id) {
+            assert_eq!(
+                item.stage.dir_name(),
+                "5_done",
+                "Story should remain in 5_done after stale mergemaster advance"
+            );
+        }
+    }
 }