undefined path requests

### Site

https://fedi.woodpeckersnest.space/

### Version

2026.08.08.e6a2887a

### Instance

https://fedi.woodpeckersnest.space/

### Browser

Brave: 1.93.138 (Aug 21, 2026)

### Bug description

Aug 21 21:17:33 pandora.woodpeckersnest.space nginx[692455]: pandora.woodpeckersnest.space fedi: 2026/08/21 21:17:33 [error] 692455#692455: *96989 open() "/var/www/phanpy/undefined" failed (2: No such file or directory), client: fd42:42:42::20, server: fedi.woodpeckersnest.space, request: "GET /undefined HTTP/2.0", host: "fedi.woodpeckersnest.space", referrer: "https://fedi.woodpeckersnest.space/"

### To reproduce

I am not sure how to reproduce, I found the logs only today.

### Expected behavior

_No response_

### Other

_No response_

No source file or test is named. Start by tracing the client-side navigation and request construction that could produce a GET request for /undefined, using the supplied nginx log as the initial reproduction target. Done means the source of the undefined path is identified and the affected flow no longer emits such requests.

Written by the indexing model from the issue text.