layout.tsx renders twice when using SSR and parallel routes

### Link to the code that reproduces this issue https://github.com/eiiot/next-routes-rerendering ### To Reproduce 1. Build the application with `next build` 2. Run with `next start` ### Current vs. Expected behavior `RootLayout rendered` is logged twice per request when it should only be logged once. This causes a bunch of issues, including fetching data from APIs twice. ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:03:11 PDT 2024; root:xnu-11215.41.3~2/RELEASE_ARM64_T6020 Available memory (MB): 32768 Available CPU cores: 12 Binaries: Node: 20.11.0 npm: 10.2.4 Yarn: 4.1.0 pnpm: N/A Relevant Packages: next: 15.2.0-canary.71 eslint-config-next: 15.2.0-canary.71 react: 19.0.0 react-dom: 19.0.0 typescript: 5.7.3 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Performance, Parallel & Intercepting Routes ### Which stage(s) are affected? (Select all that apply) next dev (local), next build (local), next start (local), Vercel (Deployed) ### Additional context This seems to be a fairly old issue: see [this reddit thread](https://www.reddit.com/r/nextjs/comments/187h837/are_parallel_routes_broken_in_v14/) discussing v14.