Catch generic exception when export to pdf

[Light2Dark]

📝 Summary

Relates to #8700.

We previously only checked for OSError. It seems that this isn't sufficient to capture missing Pandoc. So instead, we catch a generic exception. Standard PDF tends to be quite strict anyway compared to WebPDF, so this is a good fallback

🔍 Description of Changes

📋 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.
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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Mar 16, 2026 4:53pm

[Copilot]

Pull request overview

Updates the server-side PDF export flow to fall back to WebPDFExporter when standard nbconvert.PDFExporter fails due to non-OSError conversion issues (e.g., missing Pandoc), and adds a regression test for that fallback.

Changes:

• Broaden standard PDF export failure handling from OSError to Exception to trigger webpdf fallback for more nbconvert conversion errors.
• Add a test ensuring PandocMissing triggers fallback to WebPDFExporter.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
marimo/_server/export/exporter.py	Catch generic exceptions during standard PDF export and warn + fall back to webpdf.
tests/_server/export/test_exporter.py	Add regression test for fallback behavior when PandocMissing is raised.

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[Copilot]

Pull request overview

Improves Marimo’s PDF export reliability by expanding failure handling for “standard” nbconvert PDF generation (pandoc/TeX) and validating fallback to WebPDF.

Changes:

• Catch additional nbconvert conversion exceptions (including pandoc-missing scenarios) and fall back to WebPDF.
• Add test coverage for fallback behavior on conversion and unexpected errors.
• Update PDF export tests’ dependency skip conditions (now including playwright).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
marimo/_server/export/exporter.py	Expands exception handling in export_as_pdf to fall back to WebPDF when standard PDF conversion fails.
tests/_server/export/test_exporter.py	Adjusts skip conditions and adds new tests covering fallback behavior for additional exception types.

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[Light2Dark]

we should probably add nbconvert to our test-optional group

[mscolnick]

sounds good, ill add in a followup