Describe the bug

When using marimo’s code_mode API, ctx.edit_cell(...) and ctx.create_cell(...) appear to auto-format changed Python code before applying it, even when the user config has:

[save]
format_on_save = false

In my case this is surprising because I’m using code_mode for very local structural edits in a live notebook, and carefully formatted compact code gets rewritten by ruff format / black.

From reading the source, this seems to happen in _code_mode/_context.py, where _format_plan(...) always runs changed code through DefaultFormatter(...) if a formatter is available, using only formatting.line_length from config.

That means:

• save.format_on_save = false does not prevent formatting for code-mode edits
• code-mode formatting is effectively always on when ruff or black is installed

Expected
One of:

1. code_mode respects save.format_on_save
2. code_mode exposes an explicit format=False option on edit_cell / create_cell
3. marimo adds a separate config key for API/code-mode formatting

Actual
ctx.edit_cell(...) reformats code unconditionally (subject to formatter availability), even when save-formatting is disabled.

Issues
For notebooks that intentionally use dense/compact source layout, code-mode edits currently cannot preserve author formatting. This is especially frustrating when using the marimo-pair skill.

Will you submit a PR?

• Yes

Environment

marimo 0.23.2
installed via uvx
save.format_on_save = false
formatting.line_length = 79
ruff available

Code to reproduce

[save]
format_on_save = false