afterNavigate callbacks do not get removed when returning a function in onNavigate

[Elia872]

Describe the bug

When returning a function from an onNavigate callback in a parent layout, a child afterNavigate does not get removed during a page change.

Reproduction

https://github.com/Elia872/kit-afternav-error

navigate by clicking links back and forth from /a and /b, and see how in the console each time the number of logs increases. Also see the "after navigate was called" in /b, it should be false, but the code in /a's afterNavigate changes it to true.

Logs

No response

System Info

System:
    OS: Linux 6.8 Linux Mint 22 (Wilma)
    CPU: (32) x64 AMD Ryzen 9 5950X 16-Core Processor
    Memory: 19.20 GB / 31.23 GB
    Container: Yes
    Shell: 3.7.1 - /usr/bin/fish
  Binaries:
    Node: 20.16.0 - ~/.local/share/pnpm/node
    npm: 10.8.1 - ~/.local/share/pnpm/npm
    pnpm: 9.15.1 - ~/.local/share/pnpm/pnpm
    bun: 1.1.18 - ~/.bun/bin/bun
    Watchman: 4.9.0 - /usr/bin/watchman
  Browsers:
    Chrome: 131.0.6778.139
  npmPackages:
    @sveltejs/adapter-auto: ^3.0.0 => 3.3.1
    @sveltejs/kit: ^2.0.0 => 2.15.0
    @sveltejs/vite-plugin-svelte: ^4.0.0 => 4.0.4
    svelte: ^5.0.0 => 5.16.0
    vite: ^5.4.11 => 5.4.11

Severity

serious, but I can work around it

Additional Information

No response