diff --git a/server-rs/crates/spacetime-module/src/migration.rs b/server-rs/crates/spacetime-module/src/migration.rs
index 62b5e11f7..c3e4605a5 100644
--- a/server-rs/crates/spacetime-module/src/migration.rs
+++ b/server-rs/crates/spacetime-module/src/migration.rs
@@ -1938,6 +1938,19 @@ mod migration_bootstrap_secret_tests {
         assert_eq!(normalized["warning_message"], serde_json::Value::Null);
     }
 
+    /// 旧迁移包的 external_generation_job 没有 provider checkpoint 两列：导入后必须都是
+    /// null（等同 `#[default(None)]`），否则 at-most-once submit 会把旧任务误判成已提交。
+    #[test]
+    fn old_external_generation_job_rows_default_to_unsubmitted_provider() {
+        let normalized = normalize_migration_row(
+            "external_generation_job",
+            &serde_json::json!({ "job_id": "task-1" }),
+        );
+
+        assert_eq!(normalized["provider_kind"], serde_json::Value::Null);
+        assert_eq!(normalized["provider_task_id"], serde_json::Value::Null);
+    }
+
     #[test]
     fn old_editor_canvas_rows_default_to_legacy_storage() {
         let normalized = normalize_migration_row(