1 files changed, 18 insertions, 7 deletions

diff --git a/src/swarm/sync.rs b/src/swarm/sync.rs
index 3284015..80d6d56 100644
--- a/src/swarm/sync.rs
+++ b/src/swarm/sync.rs
@@ -32,6 +32,12 @@ pub(crate) struct ChangeSet {
 }
 
 async fn deliver_sync_to_peer(state: &AppState, peer: &str) -> Result<()> {
+    if state.remake.fetching_snapshot() {
+        // Rejoining: the snapshot comes as a download, not in a sync message. Sync
+        // starts once it is here (`remake::catchup`).
+        trace!("Waiting for the snapshot download; not syncing yet");
+        return Ok(());
+    }
     let Some(peer_state_mutex) = state.get_peer_state(peer).await else {
         trace!("Peer was forgotten; skipping synchronization");
         return Ok(());
@@ -337,7 +343,7 @@ pub(crate) async fn handle_sync(
 
             let mut peer_state = peer_state_mutex.blocking_lock();
             peer_state.reports_ready = Some(from_ready);
-            let heads_before = replica.doc.get_heads();
+            let heads_before = replica.heads().to_vec();
 
             replica
                 .doc
@@ -354,7 +360,8 @@ pub(crate) async fn handle_sync(
             peer_state.sync.reply_settled();
 
             resend_if_needed(&peer, &mut peer_state.sync.state);
-            let heads_after = replica.doc.get_heads();
+            replica.refresh_heads();
+            let heads_after = replica.heads().to_vec();
             stats.heads_seen(heads_after.len());
             let changed = heads_after != heads_before;
             if changed && measure_propagation {
@@ -372,8 +379,11 @@ pub(crate) async fn handle_sync(
             }
 
             Ok(Some((
-                // Only from a ready peer: a peer still catching up has empty heads, which
-                // every document "contains".
+                // Only from a ready peer, and only if it has heads at all: empty heads are
+                // "contained" in every document, so they prove nothing. A peer still
+                // catching up has them, and so does a ready peer whose document is empty
+                // (a misconfigured second swarm, or a genesis node in its first seconds,
+                // before it registered itself).
                 check_caught_up
                     && from_ready
                     && peer_state
@@ -382,9 +392,10 @@ pub(crate) async fn handle_sync(
                         .their_heads
                         .as_ref()
                         .is_some_and(|heads| {
-                            heads
-                                .iter()
-                                .all(|h| replica.doc.get_change_by_hash(h).is_some())
+                            !heads.is_empty()
+                                && heads
+                                    .iter()
+                                    .all(|h| replica.doc.get_change_by_hash(h).is_some())
                         }),
                 changed,
             )))