sync: a message carries the signatures of its changes

A sync message carried the signatures its peer wasn't sent yet, by a
cursor per peer. Changes sent again, as after a message taken as
delivered and lost on the way, went without them: the peer was past
them. Under a policy requiring signatures they waited until the
writer's next signed change, or the next session.

A message now carries the signatures of the changes it carries
(Signatures::for_changes), whatever the peer was sent before: changes
sent again arrive vouched for as the first time. Past 256 (a message
carrying the batches of many writers), each writer's latest instead,
as a delta carries. The cursor goes, and with it resetting it after a
failed send or a new session.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index a7a466b..e9afe06 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -983,11 +983,11 @@ impl SyncSession {
         self.state.their_heads.is_none() && we_ready && peer_ready == Some(false)
     }
 
-    /// Whether the message just generated (`generate`) carries changes.
-    pub(crate) fn carrying(&self) -> bool {
+    /// The changes the message just generated (`generate`, `push`) carries.
+    pub(crate) fn carried(&self) -> &[crate::document::ChangeHash] {
         self.sending
             .as_ref()
-            .is_some_and(|sending| !sending.sent.is_empty())
+            .map_or(&[], |sending| sending.sent.as_slice())
     }
 
     /// Which session this is: a message generated from it reports its send's outcome