fix: specify utf-8 encoding when writing toml files

[daizutabi]

📝 Summary

Fixes #6434.
Fixes a UnicodeEncodeError on Windows by specifying UTF-8 encoding when writing TOML files.

🔍 Description of Changes

This pull request addresses an issue where saving a marimo notebook on Windows with a file path containing non-ASCII characters would result in a UnicodeEncodeError.

The error was caused by the write_toml function in marimo/_utils/config/config.py, which did not specify the file encoding when writing the TOML configuration. This led to issues on operating systems where the default encoding is not UTF-8.

The fix involves explicitly setting the encoding to utf-8 in the write_text method call within the write_toml function. This ensures consistent behavior across all platforms and prevents encoding-related errors.

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

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Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Sep 19, 2025 7:54pm