From 2cfd2a3531e7df2dae4d9821b1b733756b659eb0 Mon Sep 17 00:00:00 2001
From: "Dylan M. Taylor" <dylan@dylanmtaylor.com>
Date: Wed, 11 Nov 2026 19:16:24 +0000
Subject: [PATCH] collab-net: hand the sync client the bounded roster; assert
 the kept prefixes

---
 crates/collab-net/src/client_cap_tests.rs | 26 +++++++++++++++++++++--
 crates/collab-net/src/join.rs             |  4 ++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/crates/collab-net/src/client_cap_tests.rs b/crates/collab-net/src/client_cap_tests.rs
index 73f181774..5af7c7a2f 100644
--- a/crates/collab-net/src/client_cap_tests.rs
+++ b/crates/collab-net/src/client_cap_tests.rs
@@ -4,7 +4,7 @@
 
 use std::sync::{Arc, Mutex};
 
-use figcraft_collab::message::{Peer, Presence, ServerMsg};
+use figcraft_collab::message::{Access, CatchUp, Peer, Presence, Processed, ServerMsg};
 use figcraft_engine::live::{Event, MAX_PEERS};
 
 use crate::guest::GuestConfig;
@@ -69,7 +69,29 @@ fn a_hosts_long_names_and_colours_are_cut_where_they_are_kept() {
     let long = "x".repeat(100_000);
     take(ServerMsg::PeerJoined(Peer { client_id: 1, name: long.clone(), color: long }), &cfg, &inbox, &mut seen, &resume, &|| {});
     match inbox.drain().as_slice() {
-        [Event::PeerJoined(p)] => assert!(p.name.chars().count() <= 256 && p.color.chars().count() <= 32),
+        [Event::PeerJoined(p)] => assert_eq!((p.name.as_str(), p.color.as_str()), ("x".repeat(256).as_str(), "x".repeat(32).as_str())),
         other => panic!("{other:?}"),
     }
 }
+
+#[test]
+fn the_welcome_handed_to_the_sync_client_carries_the_bounded_roster() {
+    let inbox = inbox();
+    let cfg = GuestConfig::new(Invite::new("127.0.0.1:47900", "0123456789abcdef", "AbCdEfGhIjKlMnOpQrStUv"), "Ada".into());
+    let resume = Mutex::new(None);
+    let long = "y".repeat(100_000);
+    let welcome = ServerMsg::Welcome {
+        session: 1,
+        client_id: 9,
+        seq: 0,
+        catch_up: CatchUp::Snapshot(Vec::new()),
+        processed: Processed::default(),
+        peers: vec![Peer { client_id: 1, name: long.clone(), color: long }],
+        access: Access::default(),
+        secret: 0,
+    };
+    take(welcome, &cfg, &inbox, &mut Seen::default(), &resume, &|| {});
+    let events = inbox.drain();
+    let Some(Event::Sync(ServerMsg::Welcome { peers, .. })) = events.iter().find(|e| matches!(e, Event::Sync(_))) else { panic!("{events:?}") };
+    assert_eq!(peers.first().map(|p| (p.name.chars().count(), p.color.chars().count())), Some((256, 32)));
+}
diff --git a/crates/collab-net/src/join.rs b/crates/collab-net/src/join.rs
index 5982ed6e8..b5de889f9 100644
--- a/crates/collab-net/src/join.rs
+++ b/crates/collab-net/src/join.rs
@@ -281,6 +281,10 @@ pub(crate) fn take(mut m: ServerMsg, cfg: &GuestConfig, inbox: &Inbox, seen: &mu
                 view: None,
             };
             seen.peers = peers.clone();
+            // The sync client keeps the roster of the welcome it is handed: the bounded one.
+            if let ServerMsg::Welcome { peers: sent, .. } = &mut m {
+                sent.clone_from(&peers);
+            }
             seen.info = Some(info.clone());
             welcomed();
             inbox.push(Event::Welcome { info, peers });