diff --git a/crates/application/src/model_server.rs b/crates/application/src/model_server.rs
index fd0ca51..f9abbf4 100644
--- a/crates/application/src/model_server.rs
+++ b/crates/application/src/model_server.rs
@@ -14,6 +14,7 @@ use domain::ports::{
     ModelServerRegistry, ModelServerRuntime, ProcessStatus, ProfileStore, RemotePath,
 };
 use domain::{LocalModelServerId, StopPolicy};
+use tokio::sync::{Mutex as AsyncMutex, Notify};
 
 use crate::error::AppError;
 
@@ -167,6 +168,35 @@ struct ActiveServer {
     stop_policy: StopPolicy,
 }
 
+#[derive(Debug)]
+struct InflightEnsure {
+    result: Mutex<Option<Result<EnsureLocalModelServerOutput, AppError>>>,
+    notify: Notify,
+}
+
+impl InflightEnsure {
+    fn new() -> Self {
+        Self {
+            result: Mutex::new(None),
+            notify: Notify::new(),
+        }
+    }
+
+    async fn wait(&self) -> Result<EnsureLocalModelServerOutput, AppError> {
+        loop {
+            if let Some(result) = self.result.lock().unwrap().clone() {
+                return result;
+            }
+            self.notify.notified().await;
+        }
+    }
+
+    fn complete(&self, result: Result<EnsureLocalModelServerOutput, AppError>) {
+        *self.result.lock().unwrap() = Some(result);
+        self.notify.notify_waiters();
+    }
+}
+
 /// Ensures a configured local model server is reachable, starting it when allowed.
 pub struct EnsureLocalModelServer {
     registry: Arc<dyn ModelServerRegistry>,
@@ -176,6 +206,7 @@ pub struct EnsureLocalModelServer {
     fs: Arc<dyn FileSystem>,
     events: Arc<dyn EventBus>,
     active: Mutex<HashMap<LocalModelServerId, ActiveServer>>,
+    inflight: AsyncMutex<HashMap<LocalModelServerId, Arc<InflightEnsure>>>,
     readiness: ReadinessPolicy,
 }
 
@@ -199,6 +230,7 @@ impl EnsureLocalModelServer {
             fs,
             events,
             active: Mutex::new(HashMap::new()),
+            inflight: AsyncMutex::new(HashMap::new()),
             readiness: ReadinessPolicy::default(),
         }
     }
@@ -217,6 +249,38 @@ impl EnsureLocalModelServer {
     pub async fn execute(
         &self,
         input: EnsureLocalModelServerInput,
+    ) -> Result<EnsureLocalModelServerOutput, AppError> {
+        let server_id = input.server_id;
+        let (flight, is_leader) = {
+            let mut inflight = self.inflight.lock().await;
+            if let Some(flight) = inflight.get(&server_id) {
+                (Arc::clone(flight), false)
+            } else {
+                let flight = Arc::new(InflightEnsure::new());
+                inflight.insert(server_id, Arc::clone(&flight));
+                (flight, true)
+            }
+        };
+
+        if !is_leader {
+            return flight.wait().await;
+        }
+
+        let result = self.execute_inner(input).await;
+        flight.complete(result.clone());
+        let mut inflight = self.inflight.lock().await;
+        if inflight
+            .get(&server_id)
+            .is_some_and(|current| Arc::ptr_eq(current, &flight))
+        {
+            inflight.remove(&server_id);
+        }
+        result
+    }
+
+    async fn execute_inner(
+        &self,
+        input: EnsureLocalModelServerInput,
     ) -> Result<EnsureLocalModelServerOutput, AppError> {
         let config = self
             .registry
diff --git a/crates/application/tests/model_server.rs b/crates/application/tests/model_server.rs
index 3fd9981..0abb431 100644
--- a/crates/application/tests/model_server.rs
+++ b/crates/application/tests/model_server.rs
@@ -158,11 +158,15 @@ struct FakeProcess {
     spawns: Mutex<Vec<SpawnSpec>>,
     kills: Mutex<Vec<String>>,
     statuses: Mutex<HashMap<String, ProcessStatus>>,
+    spawn_delay: Duration,
 }
 
 #[async_trait]
 impl ManagedProcess for FakeProcess {
     async fn spawn(&self, spec: SpawnSpec) -> Result<ManagedProcessHandle, ModelServerError> {
+        if !self.spawn_delay.is_zero() {
+            tokio::time::sleep(self.spawn_delay).await;
+        }
         self.spawns.lock().unwrap().push(spec);
         let handle = ManagedProcessHandle {
             id: format!("h{}", self.spawns.lock().unwrap().len()),
@@ -373,6 +377,73 @@ async fn absent_auto_start_spawns_and_waits_until_ready() {
     );
 }
 
+#[tokio::test]
+async fn concurrent_ensure_same_server_shares_one_start_attempt() {
+    let registry = Arc::new(FakeRegistry::default());
+    registry
+        .save(config(sid(10), 8090, "/models/qwen.gguf", true))
+        .await
+        .unwrap();
+    let fs = Arc::new(FakeFs::default());
+    fs.existing
+        .lock()
+        .unwrap()
+        .push("/models/qwen.gguf".to_owned());
+    let process = Arc::new(FakeProcess {
+        spawn_delay: Duration::from_millis(25),
+        ..FakeProcess::default()
+    });
+    let events = Arc::new(FakeEvents::default());
+    let usecase = Arc::new(ensure(
+        Arc::clone(&registry),
+        Arc::new(FakeProbe::new(vec![
+            ModelServerStatus::Unreachable,
+            ModelServerStatus::ReadyReused,
+        ])),
+        Arc::clone(&process),
+        fs,
+        Arc::clone(&events),
+    ));
+
+    let mut tasks = Vec::new();
+    for _ in 0..5 {
+        let usecase = Arc::clone(&usecase);
+        tasks.push(tokio::spawn(async move {
+            usecase
+                .execute(EnsureLocalModelServerInput { server_id: sid(10) })
+                .await
+                .unwrap()
+        }));
+    }
+
+    let mut outputs = Vec::new();
+    for task in tasks {
+        outputs.push(task.await.unwrap());
+    }
+
+    assert!(outputs
+        .iter()
+        .all(|out| out.ready.status == ModelServerStatus::ReadyStarted));
+    assert_eq!(process.spawns.lock().unwrap().len(), 1);
+
+    let starting_events = events
+        .0
+        .lock()
+        .unwrap()
+        .iter()
+        .filter(|event| {
+            matches!(
+                event,
+                DomainEvent::ModelServerStatusChanged {
+                    status: domain::model_server::ModelServerLifecycleStatus::Starting,
+                    ..
+                }
+            )
+        })
+        .count();
+    assert_eq!(starting_events, 1);
+}
+
 #[tokio::test]
 async fn missing_model_path_is_path_not_accessible() {
     let registry = Arc::new(FakeRegistry::default());