api: allow reading past versions

1 files changed, 3 insertions, 0 deletions

diff --git a/src/document/store.rs b/src/document/store.rs
index c2c0622..c16767b 100644
--- a/src/document/store.rs
+++ b/src/document/store.rs
@@ -94,6 +94,9 @@ pub(crate) enum StoreError {
     /// An index past a list's end (`length` items).
     #[error("index {index} is past the list's end ({length} items)")]
     PastTheEnd { index: usize, length: usize },
+    /// A read at heads the document doesn't have (`at::At`).
+    #[error("this node doesn't have these heads (yet)")]
+    UnknownHeads,
     /// The node is rejoining a newer epoch: no writes until it is done
     /// (`Replica::writable`).
     #[error("the node is rejoining a newer epoch; writes are refused until it is done")]