fix(simulation): address bridge review feedback

Replace .lock().unwrap() with .expect("mutex poisoned") in LocalBridge
for clearer panic messages. Document 16MB MAX_MESSAGE_SIZE rationale
in framing.rs with entity count sizing analysis.

Addresses Hoshe PR review suggestions.

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

server/src/bridge/framing.rs

@@ -4,7 +4,10 @@
 
 use std::io::{self, Read, Write};
 
-/// Maximum message size: 16 MB
+/// Maximum message size: 16 MB.
+/// Sized for ObserverSnapshot with ~1000 entities (each ~40 bytes serialized),
+/// plus generous headroom for future field additions. A full-map dump of 10k
+/// entities would be ~400 KB, well within this limit.
 const MAX_MESSAGE_SIZE: u32 = 16 * 1024 * 1024;
 
 /// Write a length-prefixed message to a writer.

server/src/bridge/local.rs

@@ -83,7 +83,7 @@ impl SimBridge for LocalBridge {
     fn send_snapshot(&self, snapshot: &ObserverSnapshot) -> Result<(), BridgeError> {
         let payload = rmp_serde::to_vec(snapshot)?;
 
-        let mut writer = self.writer.lock().unwrap();
+        let mut writer = self.writer.lock().expect("writer mutex poisoned");
         write_framed(writer.get_mut(), &payload)?;
 
         tracing::trace!("sent snapshot: tick={}", snapshot.tick);
@@ -91,7 +91,7 @@ impl SimBridge for LocalBridge {
     }
 
     fn receive_inputs(&self) -> Result<Vec<PlayerInput>, BridgeError> {
-        let mut reader = self.reader.lock().unwrap();
+        let mut reader = self.reader.lock().expect("reader mutex poisoned");
 
         match read_framed(reader.get_mut())? {
             Some(payload) => {