Merge remote-tracking branch 'origin/ci'

# Conflicts:
#	client/tests/fixtures/msgpack/snapshot_boundary_tick_0.msgpack
#	client/tests/fixtures/msgpack/snapshot_boundary_tick_127.msgpack
#	client/tests/fixtures/msgpack/snapshot_boundary_tick_2b31m1.msgpack
#	client/tests/fixtures/msgpack/snapshot_boundary_tick_2b32.msgpack
#	client/tests/fixtures/msgpack/snapshot_boundary_tick_32767.msgpack
#	client/tests/fixtures/msgpack/snapshot_empty.msgpack
#	client/tests/fixtures/msgpack/snapshot_multi_entity.msgpack
#	client/tests/fixtures/msgpack/snapshot_one_npc.msgpack
#	client/tests/fixtures/msgpack/snapshot_player.msgpack
#	client/tests/fixtures/msgpack/snapshot_v2_full.msgpack
#	server/Cargo.toml
#	server/src/bridge/text_renderer.rs
#	server/src/bridge/types.rs
#	server/src/perception/observer/mod.rs
#	server/src/simulation/path_follow.rs
#	server/tests/bridge_ipc.rs
#	server/tests/bridge_tcp.rs
#	server/tests/gen_fixtures.rs
#	server/tests/serialization.rs

server/src/bridge/text_renderer.rs

@@ -300,6 +300,7 @@ mod tests {
             blocked_entities: vec![],
             scan_events: vec![],
             sound_events: vec![],
+            rng_seed: None,
         }
     }
 
@@ -424,6 +425,7 @@ mod tests {
             blocked_entities: vec![],
             scan_events: vec![],
             sound_events: vec![],
+            rng_seed: None,
         };
         let text = format_snapshot_text(&snap);
         assert!(text.contains("Tick 0"));

server/src/bridge/types.rs

@@ -28,7 +28,9 @@ pub const PROTOCOL_VERSION: u8 = 10;
 /// v7 adds: pending_recognitions (#423, D-060 cognitive delay).
 /// v8 adds: dialogue_response (#305, D-028 dialogue pipeline).
 /// v9 adds: blocked_entities (#514, debug field for LOS-blocked entities).
-/// v10 adds: sound_events (#124, D-038 server sound event pipeline).
+/// v10 adds: sound_events (#124, D-038 server sound event pipeline),
+///           rng_seed (#527, deterministic replay — completes WRONG button loop).
+/// Future fields: ambient sound events, HUD state (D-020 expansion).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ObserverSnapshot {
     /// Protocol version for forward compatibility. Current: 10.
@@ -85,6 +87,11 @@ pub struct ObserverSnapshot {
     /// Empty when no sounds are in range.
     #[serde(default)]
     pub sound_events: Vec<crate::simulation::sound::SoundEvent>,
+    /// RNG seed active at this tick for deterministic replay (#527).
+    /// The WRONG button writes this to seed.txt so replays reproduce observed bugs.
+    /// None when the RNG resource is unavailable (should not occur in practice).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub rng_seed: Option<u64>,
 }
 
 /// Game time data for client display (D-031)