diff --git a/server/src/main.rs b/server/src/main.rs
index 8cb12aa60..89e409881 100644
--- a/server/src/main.rs
+++ b/server/src/main.rs
@@ -184,9 +184,6 @@ fn main() {
     tracing::info!("Simulation server shutting down");
 }
 
-/// Print bevy_ecs schedule graph and exit.
-/// Invoked by --dump-schedule CLI flag (#346).
-///
 /// Print bevy_ecs schedule graph and exit.
 /// Invoked by --dump-schedule CLI flag (#346).
 ///
diff --git a/server/tests/serialization.rs b/server/tests/serialization.rs
index 7addfa2e7..e945e1201 100644
--- a/server/tests/serialization.rs
+++ b/server/tests/serialization.rs
@@ -1187,6 +1187,80 @@ fn v8_payload_deserializes_into_v9_struct() {
     );
 }
 
+/// rng_seed round-trips through MessagePack (#527).
+/// Verifies Some(seed) survives the wire and None is omitted.
+#[test]
+fn rng_seed_roundtrip() {
+    let mut snapshot = test_snapshot(0, vec![]);
+    snapshot.rng_seed = Some(123456789);
+    let bytes = rmp_serde::to_vec_named(&snapshot).expect("serialize");
+    let decoded: ObserverSnapshot = rmp_serde::from_slice(&bytes).expect("deserialize");
+    assert_eq!(decoded.rng_seed, Some(123456789));
+
+    // None case: skip_serializing_if omits the field, default restores it
+    let mut snapshot_none = test_snapshot(0, vec![]);
+    snapshot_none.rng_seed = None;
+    let bytes_none = rmp_serde::to_vec_named(&snapshot_none).expect("serialize");
+    let decoded_none: ObserverSnapshot = rmp_serde::from_slice(&bytes_none).expect("deserialize");
+    assert_eq!(decoded_none.rng_seed, None);
+}
+
+/// v9 payloads (without rng_seed) must deserialize into the v10 struct
+/// via #[serde(default)]. Guards backwards compat during migration (#527).
+#[test]
+fn v9_payload_deserializes_into_v10_struct() {
+    #[derive(serde::Serialize)]
+    struct ObserverSnapshotV9 {
+        version: u8,
+        tick: u64,
+        game_time: GameTime,
+        player_facing: FacingDirection,
+        player_stance: MovementStance,
+        player_inventory: Vec<InventoryItem>,
+        entities: Vec<VisibleEntity>,
+        visible_tiles: Vec<VisibleTile>,
+        nearby_interactions: Vec<NearbyInteraction>,
+        current_monologue: Option<MonologueEvent>,
+        pending_recognitions: Vec<PendingRecognitionWire>,
+        dialogue_response: Option<DialogueResponseEvent>,
+        blocked_entities: Vec<u64>,
+        scan_events: Vec<settled_reach_server::simulation::contraband::ScanEvent>,
+    }
+
+    let v9 = ObserverSnapshotV9 {
+        version: 9,
+        tick: 200,
+        game_time: GameTime {
+            day: 0,
+            time_of_day: 0,
+            day_phase: DayPhase::Morning,
+            tick_rate: TickRate::Full,
+        },
+        player_facing: FacingDirection::North,
+        player_stance: MovementStance::Walk,
+        player_inventory: vec![],
+        entities: vec![],
+        visible_tiles: vec![],
+        nearby_interactions: vec![],
+        current_monologue: None,
+        pending_recognitions: vec![],
+        dialogue_response: None,
+        blocked_entities: vec![],
+        scan_events: vec![],
+    };
+
+    let bytes = rmp_serde::to_vec_named(&v9).expect("serialize v9");
+    let decoded: ObserverSnapshot = rmp_serde::from_slice(&bytes)
+        .expect("v9 payload should deserialize into v10 struct via serde(default)");
+
+    assert_eq!(decoded.version, 9, "version field preserved from v9");
+    assert_eq!(decoded.tick, 200);
+    assert_eq!(
+        decoded.rng_seed, None,
+        "missing rng_seed should default to None"
+    );
+}
+
 /// NearbyInteraction.object_type round-trips through MessagePack (#422).
 /// Verifies object_type=Some(Container) survives the wire.
 #[test]