Task 7 scoped out reusing the F7.1 (#22) intra-diagram mermaid diff in the
built-in Markdown preview's mermaid fence rendering; Task 8 then deleted the
webview that still had it, leaving mermaidDiff.ts/mermaidFlowchartDiff.ts/
mermaidSequenceDiff.ts production-dead. Wires diffMermaid into
cowritingMarkdownItPlugin's options.highlight override via a per-render
mermaid-fence queue (built in the core rule where state.env is visible,
consumed by highlight in fence-encounter order — highlight itself has no env
param) so a mermaid fence changed since the F6/F7 baseline is re-emitted with
classDef/class/linkStyle styling directives + legend before mermaid.js ever
sees it, reusing diffBlocks' baseline/current block pairing (same pairing
renderReview used). Unchanged diagrams, disabled annotations, no baseline, and
pinned-zero-diff all pass through verbatim.
Ports the substance of the 6 mermaid-diff assertions Task 8 deleted with the
webview's E2E suite as pure unit tests in previewAnnotations.test.ts instead
(DOM-free, source-level).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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