next.js

27674179 - Skip empty parallel route slot directories instead of erroring

Skip empty parallel route slot directories instead of erroring Empty @-prefixed directories with no route files (e.g. leftover empty directories from branch switches) caused a build error requiring a default.js. Both webpack and Turbopack now check that @-slot directories contain actual route files before treating them as parallel route slots. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>