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/simulation/input.rs

@@ -314,6 +314,11 @@ pub fn process_player_input(
             }
             PlayerAction::SaveGame { ref path } => {
                 if let Some(ref mut sl) = save_load {
+                    if sl.pending.is_some() {
+                        tracing::warn!(
+                            "SaveGame overwrites already-pending save/load command (dropped)"
+                        );
+                    }
                     sl.pending = Some(SaveLoadCommand::Save {
                         path: std::path::PathBuf::from(path),
                     });
@@ -324,6 +329,11 @@ pub fn process_player_input(
             }
             PlayerAction::LoadGame { ref path } => {
                 if let Some(ref mut sl) = save_load {
+                    if sl.pending.is_some() {
+                        tracing::warn!(
+                            "LoadGame overwrites already-pending save/load command (dropped)"
+                        );
+                    }
                     sl.pending = Some(SaveLoadCommand::Load {
                         path: std::path::PathBuf::from(path),
                     });