Summary

When formatting Python files with large tuples (>20K chars), the cursor jumps to the end of file. This only happens when:

1. The tuple is very large (>20K characters)
2. The formatter makes significant changes, causing a delay
3. The cursor is positioned INSIDE the large tuple when formatting is triggered

I've tested that:

• Reducing tuple size to <20K chars fixes the issue
• Files with 30K+ char tuples but minimal formatting changes don't have this issue

The problem seems related to both tuple size AND amount of reformatting needed.

Reproducible with this file:
https://github.com/MMD-Blender/blender_mmd_tools/blob/6ae13d6039763b6813832622c13da464983e93b3/mmd_tools/m17n.py

Version

VS Code: 1.99.3
Ruff extension: 2025.22.0
OS: Windows_NT x64 10.0.19045