Defer promotion snapshots to campaign activation

src/routes/api/campaigns/[id]/+server.ts

@@ -15,7 +15,7 @@ export async function GET({ params }: { params: { id: string } }) {
     // it opens the diff viewer.
     const files = db()
         .prepare(
-            `SELECT id, server, verb, rel_path, sha256_before, sha256_after,
+            `SELECT id, server, verb, rel_path, sha256_before, sha256_after, snapshot_pending,
                     LENGTH(content_before) AS size_before,
                     LENGTH(content_after)  AS size_after,
                     COALESCE((SELECT state FROM staged_file_changes WHERE deployment_file_id = deployment_files.id), 'applied') AS apply_state

src/routes/api/campaigns/[id]/file/[fileId]/+server.ts

@@ -10,7 +10,7 @@ export async function GET({ params }: { params: { id: string; fileId: string } }
     }
     const row = db()
         .prepare(
-            `SELECT verb, rel_path, sha256_before, sha256_after, content_before, content_after
+            `SELECT verb, rel_path, sha256_before, sha256_after, content_before, content_after, snapshot_pending
              FROM deployment_files
              WHERE deployment_id = ? AND id = ?`
         )
@@ -22,9 +22,11 @@ export async function GET({ params }: { params: { id: string; fileId: string } }
               sha256_after: string | null;
               content_before: Buffer | null;
               content_after: Buffer | null;
+              snapshot_pending: number;
           }
         | undefined;
     if (!row) throw error(404, 'file not found');
+    if (row.snapshot_pending) return json({ error: 'The rollback snapshot is not available yet. It is captured immediately before file activation.' }, { status: 409 });
 
     return json({
         verb: row.verb,