fix: unwrap top-level paragraph HTML in ipynb markdown import

[api2062]

📝 Summary

Fixes #8651.

When converting some .ipynb notebooks, markdown cells that are stored as HTML paragraph blocks (e.g. <p>...</p>) are imported literally into mo.md(...). This leaves raw HTML tags in converted notebooks and can interfere with normal markdown/LaTeX rendering.

This PR normalizes markdown sources that are entirely top-level paragraph blocks before conversion.

🔍 Description of Changes

• added _normalize_paragraph_html() in marimo/_convert/common/format.py
• applied normalization in markdown_to_marimo() before markdown code generation
• normalization is intentionally scoped:
  • applies only when the markdown source is composed entirely of top-level <p>...</p> blocks
  • converts those blocks into plain markdown paragraphs separated by blank lines
  • leaves mixed/other HTML (e.g. <div><p>...</p></div>) unchanged
• added regression tests:
  • tests/_convert/common/test_convert_format.py
    • test_markdown_to_marimo_unwraps_top_level_paragraph_html
    • test_markdown_to_marimo_keeps_non_paragraph_html
  • tests/_convert/ipynb/test_ipynb_to_ir.py
    • test_convert_ipynb_markdown_unwraps_top_level_paragraph_html

✅ Validation

• reproduced using the exact notebook from the issue (SM_sphere_S2.ipynb)
• before fix: converted output contained raw <p> / </p> tags
• after fix: converted output no longer contains those tags
• ran targeted tests for new behavior: passed

📋 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).
• Tests have been added for the changes made.
• Documentation has been updated where applicable, including docstrings for API changes.
• Pull request title is a good summary of the changes - it will be used in the release notes.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Mar 15, 2026 10:29pm

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