sync: signatures go with changes only

A sync message took the signatures its peer wasn't sent yet whenever it
had a body, an Automerge message saying only what we have included. A
signature belongs with the changes it vouches for: they go along the
trees, and a peer that got them elsewhere got the signatures with them.

Signatures now go in a message that carries changes (pushed, offered
as a delta, or in an Automerge message carrying some: SyncSession::
carrying), and in no other.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/document/sync.rs b/src/document/sync.rs
index 394b10a..440718c 100644
--- a/src/document/sync.rs
+++ b/src/document/sync.rs
@@ -983,6 +983,13 @@ 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 {
+        self.sending
+            .as_ref()
+            .is_some_and(|sending| !sending.sent.is_empty())
+    }
+
     /// Which session this is: a message generated from it reports its send's outcome
     /// with this (`send_succeeded`, `send_failed`).
     pub(crate) fn id(&self) -> u64 {