fix(collab-net): keep the client's message cap in range on 32-bit targets

apps/figcraft-server/src/public_tests.rs

@@ -506,6 +506,8 @@ fn files_above_64_mib_fit_every_limit() {
         assert!(net.max_reading_total >= net.max_reading_block && net.max_queued_total >= net.max_queued_block);
         assert!(core.max_message_bytes > file, "open={open_publish}: {}", core.max_message_bytes);
     }
-    // A client takes the largest file any server can keep.
-    assert!(NetLimits::default().max_server_message > 4096 << 20);
+    // A client takes the largest file any server can keep, or as much as a 32-bit target can address
+    // (computed in u64: `4097 << 20` in a 32-bit usize wraps to 1 MiB).
+    let client = NetLimits::default().max_server_message as u64;
+    assert!(client > 4096 << 20 || client == u64::from(u32::MAX), "{client}");
 }

crates/collab-net/src/limits.rs

@@ -14,7 +14,8 @@ pub struct NetLimits {
     pub max_hello: usize,
     /// Largest message a client accepts from the host (a welcome carries the whole document): the
     /// largest file a `figcraft-server` can be set to keep (`max_file_mb`, at most 4096) and a margin,
-    /// so a client can open every file a server takes.
+    /// so a client can open every file a server takes; on a 32-bit target (the browser) as much as
+    /// `usize` holds.
     pub max_server_message: usize,
     /// Messages a client may send per second on average, and in a burst; beyond that it is
     /// disconnected.
@@ -63,7 +64,7 @@ impl Default for NetLimits {
             max_connections: 64,
             max_client_message: figcraft_collab::Limits::default().max_message_bytes,
             max_hello: 64 << 10,
-            max_server_message: 4097 << 20,
+            max_server_message: usize::try_from(4097u64 << 20).unwrap_or(usize::MAX),
             rate: 100.0,
             burst: 400.0,
             hello_timeout: Duration::from_secs(10),