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/src/main.rs

@@ -11,7 +11,7 @@ use bevy_app::prelude::*;
 use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 use settled_reach_server::bridge::tcp::TcpBridge;
-use settled_reach_server::bridge::{BridgePlugin, BridgeResource, ServerRunning};
+use settled_reach_server::bridge::{BridgePlugin, BridgeResource, HandshakeState, ServerRunning};
 use settled_reach_server::simulation::SimulationPlugin;
 
 fn main() {
@@ -121,7 +121,17 @@ fn main() {
         tracing::error!("Failed to accept: {}", e);
         std::process::exit(1);
     });
-    tracing::info!("Client connected, initializing simulation");
+    tracing::info!("Client connected, sending protocol handshake");
+
+    // Protocol handshake: first framed message on the wire (#555).
+    // Client reads this and validates protocol_version before sending any input.
+    use settled_reach_server::bridge::SimBridge;
+    bridge.send_handshake().unwrap_or_else(|e| {
+        tracing::error!("Failed to send handshake: {}", e);
+        std::process::exit(1);
+    });
+
+    tracing::info!("Handshake sent, initializing simulation");
 
     // RNG seed: test-mode defaults to 42 for deterministic replay
     let seed = seed_flag.unwrap_or(if test_mode { 42 } else { 0 });
@@ -138,6 +148,7 @@ fn main() {
     });
     app.add_plugins(settled_reach_server::content::ContentPlugin);
     app.insert_resource(BridgeResource::new(bridge));
+    app.insert_resource(HandshakeState::Complete);
 
     // Override SimRng with the chosen seed (SimulationPlugin defaults to seed 0)
     app.insert_resource(settled_reach_server::simulation::rng::SimRng::new(seed));