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/bridge/local.rs

@@ -80,6 +80,21 @@ impl LocalBridge {
 }
 
 impl SimBridge for LocalBridge {
+    fn send_handshake(&self) -> Result<(), BridgeError> {
+        use super::types::{HandshakeMessage, PROTOCOL_VERSION};
+        let msg = HandshakeMessage {
+            protocol_version: PROTOCOL_VERSION,
+        };
+        let payload = rmp_serde::to_vec_named(&msg)?;
+        let mut writer = self
+            .writer
+            .lock()
+            .map_err(|e| BridgeError::MutexPoisoned(format!("writer: {}", e)))?;
+        write_framed(writer.get_mut(), &payload)?;
+        tracing::info!("sent handshake: protocol_version={}", PROTOCOL_VERSION);
+        Ok(())
+    }
+
     fn send_snapshot(&self, snapshot: &ObserverSnapshot) -> Result<(), BridgeError> {
         let payload = rmp_serde::to_vec_named(snapshot)?;