[BUG] `export const dynamicParams = false` does not work with fallback rewrites

[lauri865]

Describe the bug

When setting export const dynamicParams = false on a [slug] route, it seems to take precedence over rewrites.fallback, which is a discrepancy to how Next.js works by default.

Steps to reproduce

1. Repro: https://github.com/lauri865/opennext-routes-repro
2. Run pnpm dev and go to http://localhost:3000/issue (works fine, you should see a Github issue page)
3. Run pnpm preview and go to http://localhost:8787/issue (witness a 404 page)

Expected behavior

If routes are statically generated, rewrites.fallback should take precedence.

@opennextjs/cloudflare version

1.0.4

Wrangler version

4.16.1

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:39 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6020
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 22.15.0
  npm: 10.9.2
  Yarn: 1.22.19
  pnpm: N/A
Relevant Packages:
  next: 15.2.0 // There is a newer version (15.3.2) available, upgrade recommended!
  eslint-config-next: N/A
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Additional context

No response

[lauri865]

If anyone knows a workaround, would really appreciate it.

[vicb]

@conico974 I guess the root cause is in the aws package, should I transfer the issue there?

[conico974]

Yeah, the issue is there

[lauri865]

Root cause – the fallback rewrites never get handled for any dynamic route, even if fallback = false: https://github.com/opennextjs/opennextjs-aws/blob/94c3fa2d8ca385231d2be77fc134f50a7032dc84/packages/open-next/src/core/routingHandler.ts#L160

[lauri865]

Not knowing anything about the codebase, this would fix it:

if (
      !(
        (isDynamicRoute && internalEvent.rawPath !== "/404") ||
        isStaticRoute ||
        isExternalRewrite
      )
) {
const fallbackRewrites = handleRewrites

Or maybe rather, since isDynamicRoute is consumed below that block as well:

const isDynamicRoute = !isExternalRewrite && foundDynamicRoute.length > 0 && internalEvent.rawPath !== "/404";