Poor error message when dynamicParams = false blocks child routes

Link to the code that reproduces this issue

https://github.com/tavurth/nextjs-dynamicparams-bugtook

To Reproduce

1. Clone the reproduction repository
2. Run npm install (or bun i)
3. Run npm run build && npm run start
4. Navigate to http://localhost:3000/en/shared/test-123
5. Observe 404 error with NoFallbackError in terminal

Current vs. Expected behavior

Current vs. Expected behavior
Current: Route returns 404 with unhelpful error message in console:

Error: Internal: NoFallbackError
    at <anonymous> (.next/server/chunks/ssr/_babdf1ac._.js:2:1128)
    at n (.next/server/chunks/ssr/_babdf1ac._.js:2:419)
    at responseGenerator (.next/server/chunks/ssr/_babdf1ac._.js:2:2770)

Expected: Either the route should work, or a clear error message should be displayed:

Error: Dynamic route segment [shareId] is blocked by parent configuration
  → app/[locale]/layout.tsx has `export const dynamicParams = false`
  → This prevents child routes from accepting dynamic parameters not in generateStaticParams
  → Solution: Set `dynamicParams = true` in parent layout, or add all shareId values to generateStaticParams

Root Cause: The parent layout (app/[locale]/layout.tsx) has export const dynamicParams = false, which inherits to all child routes. This blocks the child route (app/[locale]/shared/[shareId]/page.tsx) from accepting dynamic shareId parameters. While this is correct behavior, the error message provides no indication of the actual problem or how to fix it.

Workaround: Change dynamicParams = false to dynamicParams = true in the parent layout.

Provide environment information

╰─ Will npx --no-install next info
/bin/sh: pnpm: command not found

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:27 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6041
  Available memory (MB): 36864
  Available CPU cores: 14
Binaries:
  Node: 24.6.0
  npm: 11.5.1
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 16.1.1 // Latest available version is detected (16.1.1).
  eslint-config-next: N/A
  react: 19.2.3
  react-dom: 19.2.3
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Dynamic Routes, Error Handling, Pages Router

Which stage(s) are affected? (Select all that apply)

next start (local)

Additional context

No response

Clone the linked reproduction, run npm install, then npm run build && npm run start and visit /en/shared/test-123. Read app/[locale]/layout.tsx and app/[locale]/shared/[shareId]/page.tsx to confirm how dynamicParams and generateStaticParams interact. Done means the blocked child-route behavior produces a clear diagnostic or the documented route behavior is corrected, with coverage for this reproduction.