Docs’ recommended modal handling approach interferes with soft navigation 404 behavior

[ljuborados]

Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/amazing-tharp-23mwdj

To Reproduce

1. Start app in dev
2. Click go to nonexistent route - notice the page hasn't changed
3. Hit refresh for a hard-navigation - notice 404 gets rendered

Current vs. Expected behavior

Current

Adding a catch-all route into a slot to handle closing modals (as per the docs) breaks soft navigation to non-existent pages - Next just happily swallows the navigation, and keeps rendering the previous page.
NOTE: Hard navigation works as expected - renders a not found page.

Expected

If nothing - consistent behaviour between soft and hard navigation.
Ideally - either update docs with the correct approach of closing modals or fix the soft navigation.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.0.0: Fri Sep 15 14:41:43 PDT 2023; root:xnu-10002.1.13~1/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 18.18.2
  npm: 9.8.1
  Yarn: 1.22.22
  pnpm: 9.9.0
Relevant Packages:
  next: 15.1.6 // Latest available version is detected (15.1.6).
  eslint-config-next: 15.1.3
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.3
Next.js Config:
  output: standalone

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

Parallel & Intercepting Routes

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

next dev (local), next build (local), next start (local), Other (Deployed)

Additional context

No response