Fix upstream deletes across independent peer revision spaces

packages/dofs/src/schema/sync.ts

@@ -69,6 +69,17 @@ export const SYNC_STATEMENTS = [
     path    TEXT,
     PRIMARY KEY (k, backend)
   )`,
+  // Local revs minted by applying a pull from `backend`. A node whose
+  // rev is listed here still holds exactly what that backend sent, so
+  // a later delete from the same backend may remove it before the echo
+  // push. Rows at or below the push cursor are pruned. Created by the
+  // baseline DDL on every boot, so existing databases gain it without
+  // a migration.
+  `CREATE TABLE IF NOT EXISTS _vfs_upstream_revs (
+    backend TEXT    NOT NULL,
+    rev     INTEGER NOT NULL,
+    PRIMARY KEY (backend, rev)
+  ) WITHOUT ROWID`,
   // Durable half of a restartable sync operation. One row per
   // (backend, direction): the plan's key. A restarted iterator reads
   // this row to recover the fixed target and generation it was working