App Router: parallel route slots drop dynamic params (`catchAll`/`[...slug]`)

This issue was created by an agent analysing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-05-22).

Problem

Pages under a parallel slot with a catch-all dynamic segment receive a params object that omits the dynamic key entirely. The matched catchAll: ['sub','folder'] array is dropped both on initial SSR and on client navigations, leaving only the static keys.

Parallel slot's catchAll params key dropped from `params`

Estimated Impact

~2 test failures across the deploy suite.

Affected Test Suites

• test/e2e/app-dir/parallel-route-navigations/parallel-route-navigations.test.ts (2 failures)

Recommendation

1. Reproduce first in vinext's own test suite. Add a @slot/[...catchAll]/page.tsx and assert params.catchAll is populated on SSR and after client nav.

2. Pass dynamic params through the parallel-slot resolver. When matching parallel slots, accumulate dynamic params from the slot path into params rather than only the children path.

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Part of #1328.