App Router: residual `trailingSlash` canonical-URL / revalidation cases (follow-up to #1332)

[james-elicx]

This issue was created by an agent auditing CI failures from the Next.js Deploy Suite (vinext main vs Next.js v16.2.6, 2026-06-08).

Problem

Follow-up to the closed #1332 (trailing-slash enforcement). The core enforcement #1332 fixed is done (it dropped from ~58 failures to a few), but residual canonical-URL and revalidation interactions remain.

Affected Test Suites

• test/e2e/app-dir/trailingslash/trailingslash.test.ts (3 failures)
  • should contain trailing slash to canonical url
  • should revalidate a page with generated static params (withSlash=true)
  • should revalidate a page with generated static params (withSlash=false)
• test/e2e/basepath/trailing-slash.test.ts (1 failure)
  • should correctly replace state when same asPath but different url

Estimated impact

~4 e2e failures.

Notes

#1332 is correctly closed for the redirect/normalization core; these are canonical-URL and revalidate + generated-static-params edge cases (and a basePath history-state interaction).

Recommendation

1. Reproduce the canonical-URL trailing-slash case and the revalidate-with-generateStaticParams cases (both withSlash true/false).
2. Ensure the canonical URL and the revalidation cache key honor the trailing-slash config.