feat(daemon): snapshot writer task (Save/Remove over one channel)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/spaceshd/src/snapshot_store.rs

@@ -59,6 +59,20 @@ impl SnapshotStore for JsonSnapshotStore {
     }
 }
 
+/// Spawn the writer task; returns the sender used by the router and actors.
+pub fn spawn_writer(store: std::sync::Arc<dyn SnapshotStore>) -> tokio::sync::mpsc::UnboundedSender<SnapshotMsg> {
+    let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel::<SnapshotMsg>();
+    tokio::spawn(async move {
+        while let Some(msg) = rx.recv().await {
+            match msg {
+                SnapshotMsg::Save(sid, snap) => store.save(&sid, &snap),
+                SnapshotMsg::Remove(sid) => store.remove(&sid),
+            }
+        }
+    });
+    tx
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -120,4 +134,29 @@ mod tests {
         assert_eq!(store.load(&sid), None);
         store.remove(&sid);
     }
+
+    #[tokio::test]
+    async fn writer_saves_and_removes() {
+        let dir = tmp_dir("writer");
+        let store: std::sync::Arc<dyn SnapshotStore> = std::sync::Arc::new(JsonSnapshotStore::new(dir.clone()));
+        let tx = spawn_writer(store.clone());
+        let sid = SurfaceId("s_w".into());
+
+        tx.send(SnapshotMsg::Save(sid.clone(), sample())).unwrap();
+        let mut saved = None;
+        for _ in 0..50 {
+            if let Some(s) = store.load(&sid) { saved = Some(s); break; }
+            tokio::time::sleep(std::time::Duration::from_millis(10)).await;
+        }
+        assert_eq!(saved, Some(sample()));
+
+        tx.send(SnapshotMsg::Remove(sid.clone())).unwrap();
+        let mut gone = false;
+        for _ in 0..50 {
+            if store.load(&sid).is_none() { gone = true; break; }
+            tokio::time::sleep(std::time::Duration::from_millis(10)).await;
+        }
+        assert!(gone, "writer should have removed the snapshot file");
+        let _ = std::fs::remove_dir_all(dir);
+    }
 }