`error.routerCode` removed and not a clear replacement for `error.routerCode === 'PARSE_PARAMS'` or `error.routerCode === 'VALIDATE_SEARCH'`

Which project does this relate to?

Router

Describe the bug

In commit 2f53749 (shipped in @tanstack/react-router@1.170.10), error.routerCode was removed from the error passed to a route's onError handler. Previously, search/param validation failures could be detected like this:

export const Route = createFileRoute('/')({
  component: RouteComponent,
  params: pathParamsSchema, // Using Zod (v4) schema
  validateSearch: searchParamsSchema, // Using Zod (v4) schema
  ....
  onError: (error) => {
    if (error.routerCode === 'PARSE_PARAMS') throw redirect({ to: '/parse-error' })
    if (error.routerCode === 'VALIDATE_SEARCH') throw redirect({ to: '/validation-error' })
    throw error
  }
}

This now silently breaks because routerCode no longer exists. I would say this change is more of a breaking change as the contract has changed, but I'm unsure if it is intentional or just a bug.

Looking at the code base (guessing the change is intentionally) a possible solution to have the minimum changes and exact functionality could be:

onError: (error) => {
  if (error instanceof PathParamError) throw redirect({ to: '/' })
  if (error instanceof SearchParamError) throw redirect({ to: '/' })
  throw error
}

However,@tanstack/react-router only re-exports SearchParamError, not PathParamError it is only exported from @tanstack/router-core, forcing consumers to import from a transitive dependency (maybe is not but most likely yes):

import { SearchParamError } from '@tanstack/react-router'; // ✅ works
import { PathParamError } from '@tanstack/react-router';   // ❌ not exported
import { PathParamError } from '@tanstack/router-core';    // works, but most likely reaching into a transitive dep

Expected behavior

Either have routerCode back or re-export PathParamError from @tanstack/react-router alongside SearchParamError, so consumers don't have to import from @tanstack/router-core (which most likely is going to be a transitive dep).

If that's not correct then docs should explain the proper way to differentiate between a parse error and a validation error is provided.

Platform

• Router / Start Version: @tanstack/react-router 1.170.11 (@tanstack/router-core 1.171.9, @tanstack/router-plugin 1.168.14)
• OS: Any
• Browser: Any
• Browser Version: Any
• Bundler: vite
• Bundler Version: 8.0.16

Additional context

Maybe the usage of error instanceOf PathParamError or error instanceOf SearchParamError is not a good solution so in that case what would be a good solution?

Side note: the documentation still references the removed routerCode in Search Params guide

Start with the route onError entry point and the Search Params guide, which still references routerCode. Compare the current @tanstack/react-router exports with the error types described in the issue and review the change from commit 2f53749. Done means consumers have a documented, supported way to distinguish parse and validation failures without relying on an unavailable export or removed field.