fix: restore the production gate after the migration tasks

- rebuild editors/vscode bundles, stale since the parser escape fix
- attach the caught ParseError as `cause` in both migration validators
- drop two unused test bindings flagged by eslint

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/cli/src/migrations/apis-block.ts

@@ -276,7 +276,9 @@ export function migrateApisBlock(
     parse(after);
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error);
-    throw new Error(`apis-block migration produced source that failed to parse: ${message}`);
+    throw new Error(`apis-block migration produced source that failed to parse: ${message}`, {
+      cause: error,
+    });
   }
 
   return { source: after, changed: true };

packages/cli/src/migrations/mode-functions.ts

@@ -266,7 +266,9 @@ export function migrateModeFunctions(
       parse(after);
     } catch (error) {
       const message = error instanceof Error ? error.message : String(error);
-      throw new Error(`mode-functions migration produced source that failed to parse: ${message}`);
+      throw new Error(`mode-functions migration produced source that failed to parse: ${message}`, {
+        cause: error,
+      });
     }
   }