Improve toolbar review layout.

web/src/types.ts

@@ -121,4 +121,9 @@ export interface DiffPayload {
   // patch. `files` is still filled in, so the size can be described before
   // anything asks for it again with force. See git.Repo.Diff.
   oversized?: boolean;
+  // A digest of what this selection resolved to when the patch was made. The
+  // page holds on to it and asks the server for the current one on a timer, so
+  // it can say the diff has been overtaken instead of reloading it mid-read.
+  // Empty when the patch was withheld — nothing on screen to go stale.
+  revision?: string;
 }