1 files changed, 20 insertions, 10 deletions

diff --git a/src/remake/coordinator.rs b/src/remake/coordinator.rs
index 9bcf8ba..3a7b071 100644
--- a/src/remake/coordinator.rs
+++ b/src/remake/coordinator.rs
@@ -141,7 +141,23 @@ fn obstacle(id: &str, record: &Record, all: &[(String, Record)]) -> Option<Strin
 }
 
 async fn commit<H: Host>(host: &H, id: &str, record: &Record) -> Result<(), StoreError> {
-    let Some(mut request) = record.snapshot_request(id) else {
+    let content = match &record.proposal.content {
+        Some(reference) => match content::ensure(host, reference).await {
+            Ok(bytes) => Some(bytes),
+            Err(reason) => return decide_abort(host, id, reason).await,
+        },
+        None => None,
+    };
+
+    // Clone under the read lock, build without any lock.
+    let mut copy = host.read_doc(|doc| doc.clone()).await;
+    // A base left to the commit is what this node has now. Every node that sees the
+    // decision has it too: the decision change depends on it.
+    let (base, fixed_now) = match &record.proposal.base_heads {
+        None => (Some(copy.get_heads()), true),
+        Some(heads) => (records::decode_heads(heads), false),
+    };
+    let Some(mut request) = base.and_then(|base| record.snapshot_request_at(id, base)) else {
         return decide_abort(
             host,
             id,
@@ -149,15 +165,8 @@ async fn commit<H: Host>(host: &H, id: &str, record: &Record) -> Result<(), Stor
         )
         .await;
     };
-    if let Some(reference) = &record.proposal.content {
-        match content::ensure(host, reference).await {
-            Ok(bytes) => request.content = Some(bytes),
-            Err(reason) => return decide_abort(host, id, reason).await,
-        }
-    }
-
-    // Clone under the read lock, build without any lock.
-    let copy = host.read_doc(|doc| doc.clone()).await;
+    let base_heads = fixed_now.then(|| records::encode_heads(&request.base_heads));
+    request.content = content;
     let mut snapshot = match snapshot::build_detached(copy, request).await {
         Ok((snapshot, _copy)) => snapshot,
         Err(error) => {
@@ -170,6 +179,7 @@ async fn commit<H: Host>(host: &H, id: &str, record: &Record) -> Result<(), Stor
 
     let decision = Decision::Committed {
         to_epoch: to_epoch.into(),
+        base_heads,
         snapshot_bytes,
         decided_at: records::unix_millis(),
     };