feat(simulation): Sprint 19 — 7 server systems

Protocol handshake (#555): HandshakeMessage as first IPC frame,
HandshakeState resource, forward-compatible input handling.

State serialization (#96): serialize_npc_to_frozen/deserialize with
full D-024 axis coverage (10 new optional fields on NpcSaveState).

Scope tags (#98): ScopeTagKind enum, ScopePinned marker, automatic
assignment from KnowledgeGraph and RelationshipGraph.

Timestamp eviction (#97): LastInteractionTick, SimSpacePressure,
BinaryHeap LRU eviction respecting ScopePinned entities.

Save/load (#553): save_to_file/load_from_file via MessagePack,
SaveGame/LoadGame IPC commands, SaveLoadResultWire on snapshot.

Test infrastructure (#200): Layer 3 integration test entry point,
three-layer architecture documented per D-030.

Information boundary tests (#272): 4 negative tests proving no
passive KG leakage, LOS fog holds, tier boundary holds, save
isolation per NPC.

1063 tests passing, 0 failures.

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

server/tests/layer3.rs

@@ -72,7 +72,19 @@ fn server_subprocess_sends_snapshot_on_connect() {
     let mut reader = BufReader::new(stream.try_clone().expect("clone stream for reader"));
     let mut writer = BufWriter::new(stream);
 
-    // 4. Send one PlayerInput (idle tick 0)
+    // 4. Read the protocol handshake (first framed message, #555)
+    let handshake_frame = read_framed(&mut reader)
+        .expect("read handshake frame")
+        .expect("server closed connection before sending handshake");
+    let handshake: HandshakeMessage =
+        rmp_serde::from_slice(&handshake_frame).expect("deserialize HandshakeMessage");
+    assert_eq!(
+        handshake.protocol_version, PROTOCOL_VERSION,
+        "handshake protocol_version mismatch: got {}, expected {}",
+        handshake.protocol_version, PROTOCOL_VERSION
+    );
+
+    // 5. Send one PlayerInput (idle tick 0)
     let inputs = vec![PlayerInput {
         tick: 0,
         action: PlayerAction::MoveNorth,
@@ -80,14 +92,14 @@ fn server_subprocess_sends_snapshot_on_connect() {
     let payload = rmp_serde::to_vec_named(&inputs).expect("serialize PlayerInput");
     write_framed(&mut writer, &payload).expect("send PlayerInput to server");
 
-    // 5. Read one ObserverSnapshot
+    // 6. Read one ObserverSnapshot
     let response = read_framed(&mut reader)
         .expect("read snapshot frame")
         .expect("server closed connection before sending snapshot");
     let snapshot: ObserverSnapshot =
         rmp_serde::from_slice(&response).expect("deserialize ObserverSnapshot");
 
-    // 6. Assert protocol correctness (D-020)
+    // 7. Assert protocol correctness (D-020)
     assert_eq!(
         snapshot.version, PROTOCOL_VERSION,
         "protocol version mismatch: got {}, expected {}",
@@ -105,7 +117,7 @@ fn server_subprocess_sends_snapshot_on_connect() {
         .any(|e| matches!(e.kind, EntityKind::Player));
     assert!(has_player, "snapshot must contain a Player entity");
 
-    // 7. Clean up: drop connection so the server exits its game loop
+    // 8. Clean up: drop connection so the server exits its game loop
     drop(reader);
     drop(writer);