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Render each mermaid diagram in its own derivation - #79
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Every diagram was rendered twice, by a chromium of its own, on every build of the site, and any change to a tracked file rebuilt the site. nix/mermaid.nix now finds the mermaid blocks at evaluation time and renders each in a derivation whose only input is the diagram's text, with a placeholder for the svg id, so an edit elsewhere in the book renders nothing. mermaid_ssr.py takes the rendered svgs from MERMAID_SVG_DIR by the sha256 of their text and fills in the id, and fails on a block that nix did not find. Outside the nix build it still runs mmdc. The site is built from a file set limited to what mdbook reads, so edits to the nix files, the tests or the dictionaries leave it cached. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
bc1cindy
approved these changes
Oct 24, 2026
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Every diagram was rendered twice, by a chromium of its own, on every build of the site, and any change to a tracked file rebuilt the site.
nix/mermaid.nix now finds the mermaid blocks at evaluation time and renders each in a derivation whose only input is the diagram's text, with a placeholder for the svg id, so an edit elsewhere in the book renders nothing. mermaid_ssr.py takes the rendered svgs from MERMAID_SVG_DIR by the sha256 of their text and fills in the id, and fails on a block that nix did not find. Outside the nix build it still runs mmdc.
The site is built from a file set limited to what mdbook reads, so edits to the nix files, the tests or the dictionaries leave it cached.