`ssr: false` routes still bundle components in server output

Which project does this relate to?

Start

Describe the bug

When using Selective SSR with ssr: false on a route, the route's components are still included in the server bundle even though they'll never be server-rendered.

Example scenario:

• /app/* routes marked with ssr: false i.e all CSR routes
• These routes use a heavy client-side dependency (PlatejS editor, ~5MB)
• The editor ends up in both client and server bundles

Your Example Website or App

https://gitcms.waishanv.workers.dev/

Steps to Reproduce the Bug or Issue

1. Create a TanStack Start project with a route that has ssr: false
2. Import a heavy client-side dependency in that route (e.g., a rich text editor)
3. Run the production build (pnpm run build)
4. Inspect the server bundle output
5. Notice the client-side dependency is included in the server bundle despite ssr: false

Expected behavior

Expected: Since these routes will never SSR i.e Client Side Routes, their components shouldn't be bundled in the server output at all.

Current behavior: The ssr flag seems to only affect runtime behavior, not build-time tree-shaking.

Screenshots or Videos

No response

Platform

• Start Version: 1.150.0
• OS: Linux
• Browser: [e.g. Chrome, Safari, Firefox]
• Browser Version: Brave (chroimum - 144.0.7559.59)
• Bundler: vite: 7.1.7
• Bundler Version: [e.g. 7.0.0]

Additional context

Workaround: I'm currently stubbing out CSR-only route components in the server build via a Vite plugin (replacing them with () => null), which significantly reduces server bundle size.

Would it be feasible to make ssr: false a build-time signal/flag to exclude those route components from the server bundle?

Start with the production build for a route configured with ssr: false and inspect how that route is represented in the server bundle. Compare the server output with the route's client-only behavior and verify that a heavy client-side dependency is no longer included in the server output while the client build still contains it.