fix(simulation): PR #68 review — version bump, tracing warns, test coverage

- Bump PROTOCOL_VERSION 14 → 15 for save_result field addition
- Add tracing::warn on SaveLoadPending command overwrite (double-tap F5)
- Add tracing::warn on KnowledgeGraph::new() fallback during save
- Fix misleading WouldBlock comment in tcp.rs
- Document SimSpacePressure.active_count pre-eviction timing
- Document entity-based eviction tie-breaking non-determinism
- Add ScopePinned eviction survival regression test
- Regenerate msgpack fixtures for protocol v15

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

server/src/bridge/tcp.rs

@@ -45,7 +45,7 @@ impl TcpBridge {
         );
 
         // Set non-blocking so receive_inputs doesn't stall the game loop.
-        // read_framed handles WouldBlock by returning Ok(None).
+        // receive_inputs catches WouldBlock from read_framed and returns Ok(vec![]).
         stream
             .set_nonblocking(true)
             .map_err(|e| BridgeError::Transport(format!("failed to set non-blocking: {}", e)))?;

server/src/bridge/types.rs

@@ -17,7 +17,7 @@ pub use crate::simulation::time::{DayPhase, TickRate};
 /// negotiation is unnecessary. Client should reject snapshots with version !=
 /// PROTOCOL_VERSION. New fields use #[serde(default)] only during the migration
 /// period, then the default is removed once both sides are updated.
-pub const PROTOCOL_VERSION: u8 = 14;
+pub const PROTOCOL_VERSION: u8 = 15;
 
 /// Handshake message sent as the very first framed message after connection (#555).
 /// Client reads this before entering the normal tick loop and validates
@@ -53,7 +53,7 @@ pub struct HandshakeMessage {
 /// Future fields: ambient sound events, HUD state (D-020 expansion).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ObserverSnapshot {
-    /// Protocol version for forward compatibility. Current: 14.
+    /// Protocol version for forward compatibility. Current: 15.
     pub version: u8,
     /// Simulation tick when this snapshot was produced
     pub tick: u64,