[Bug]: Expose does not work after a while

### Platform

Linux

### Operating system version

Ubuntu 24.04

### System architecture

Intel (x86)

### PolyScope Version

0.17

### Bug description

After a couple of hours or the next day, Expose does not work.
Also, the APP_URL is red from the master polyscope.json and not the branch polyscope.json.

### Steps to reproduce

1. Start the preview
2. The next day, the preview does not work. Clicking on browse again does not initiate a new expose session.

### Relevant log output

```shell

```

Start by comparing the APP_URL values in the master and branch polyscope.json files, then trace the preview flow from starting the preview through clicking Browse and initiating an Expose session. Reproduce the next-day failure on Ubuntu 24.04 and use relevant logs to determine why Browse no longer starts a session; done means the preview still works after waiting and uses the branch APP_URL.

Rédigé par le modèle d'indexation à partir du texte de l'issue.