[Bug]: Intermittent issue: Polyscope agent does not stop after clicking Stop button

### Platform

macOS

### Operating system version

macOs Tahoe | 26.3.1 (a)

### System architecture

ARM64 (M1, M2, etc)

### PolyScope Version

Version 0.19.0 (0.19.0)

### Bug description

Occasionally, agents in Polyscope continue running for several hours and do not stop when the Stop button is clicked. This does not happen consistently but occurs often enough to disrupt normal usage.

It blocks further operations while the agent is running and forces a full restart of Polyscope to stop the agent.

It also appears that the agent is not performing any work in the background, but the running timer continues to increase.

### Steps to reproduce

_No response_

### Relevant log output

```shell

```

Non vengono forniti file sorgente, test, passaggi per la riproduzione o log. Inizia riproducendo il problema del pulsante Stop in Polyscope 0.19.0 su macOS Tahoe con ARM64, quindi traccia lo stato di esecuzione e il timer dell'agent; il lavoro è completato quando Stop termina consistently l'agent senza richiedere un riavvio completo.

Scritto dal modello di indicizzazione a partire dal testo della issue.