[faysou]

Description

Adds a mermaid-scale option that resizes Mermaid diagrams rendered as images by a percentage of their natural size. Proposed in #15069.

With mermaid-format: png or svg, Quarto sizes each diagram at its natural size at 96 dpi, so Mermaid's 16px text prints at 12pt and wide diagrams can run past the page in Typst and PDF output. fig-width scales each diagram by a different factor, so every diagram ends up with a different text size. mermaid-scale applies one factor to every diagram's natural size, which keeps diagram text the same size across a document.

---
format:
  typst:
    mermaid-format: png
    mermaid-scale: 75%
---

```{mermaid}
%%| mermaid-scale: 50%
flowchart LR
  A --> B
```

• The value is a percentage and keeps the aspect ratio. A cell value overrides the document value.
• An explicit fig-width or fig-height still takes precedence, so explicit sizes are respected as discussed in Typst: Unable to fit mermaid diagram into columns #8543.
• It applies to the png and svg outputs, where Quarto computes the size in resolveSize. With mermaid-format: js, mermaid.js sizes the diagram in the browser, so the option has no effect.
• The cell schema in the Mermaid handler and document-mermaid.yml both validate the value. A bare number or another string fails with a validation error instead of a TypeError.
• The option is skipped when the cell's options are written to the output div, like mermaid-format.

The editor tooling files under src/resources/editor/tools/ were regenerated with quarto dev-call build-artifacts.

Tests

tests/smoke/render/render-mermaid-scale.test.ts renders three copies of a diagram to Typst: one at mermaid-scale: 100%, one inheriting the document's 50%, and one with fig-width: 3. It checks that the scaled image is half the size of the 100% one and that fig-width wins. It compares against the 100% copy instead of absolute sizes, so it does not depend on the fonts headless Chrome uses. With the scaling disabled the test fails (2.13in against an expected 1.065in).

The existing Mermaid smoke-all documents (mermaid-typst, mermaid-multi-diagram, mermaid-pdf-default, mermaid-svg-docx, 13661, mermaid-gfm-svg, mermaid-gfm-default, mermaid/backticks, mermaid-themes/3328) still pass.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

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