Summary

Restores flowchart and sequence diagram code blocks in the TypeScript editor engine packages/muya (@muyajs/core), for feature parity with the legacy packages/muyajs engine the desktop app is migrating away from.

The parity gap

Legacy muyajs renders five diagram types: mermaid, plantuml, vega-lite, flowchart (flowchart.js) and sequence (js-sequence-diagrams), plus a sequenceTheme option. The TS rewrite only ported mermaid / plantuml / vega-lite — flowchart, sequence and sequenceTheme were missing. This PR brings them back, wired exactly the way the existing diagram types are.

What changed

Dependencies

• flowchart.js@^1.18.0 — the same package legacy used (pulls in pure-JS raphael, no native build).
• snapsvg-cjs@^0.0.6, underscore@^1.13.8, webfontloader@^1.6.28 — runtime deps of the vendored sequence renderer.
• dev: @types/underscore, @types/webfontloader. Ambient declarations added for flowchart.js, snapsvg-cjs, and the vendored sequence module in src/types/index.d.ts.

Sequence library: vendored, not npm

The js-sequence-diagrams name on npm is a dead security-holder placeholder (0.0.1-security, deps: none) — the real library was never published there. Legacy MarkText handled this by vendoring the library source (bramp's js-sequence-diagrams 2.0.1, BSD, wired to snap.svg). This PR vendors the same file under src/utils/diagram/sequence/ (plus its CSS and the danielbd hand-font for the 'hand' theme), kept verbatim and eslint-ignored. The file's dead jison UMD exports fallback was dropped (it's an ESM module) to avoid a Rollup COMMONJS_VARIABLE_IN_ESM warning.

Rendering pipeline

• loadRenderer learns flowchart and sequence.
• Live editor preview (diagramPreview.ts) and HTML export (markdownToHtml.ts) render both via render.parse(code).drawSVG(target, options), matching legacy and how the other diagrams are handled.
• markdownToState parses ```flowchart / ```sequence fences into diagram blocks; IDiagramMeta.type and the getHighlightHtml diagram-type list extended. Serialization already round-trips via meta.type, so no stateToMarkdown change was needed.

sequenceTheme

• Added sequenceTheme: 'hand' | 'simple' to IMuyaOptions and MUYA_DEFAULT_OPTIONS (default 'hand', matching legacy config/index.js), and pass it through when rendering sequence diagrams (preview + export).

Menu entries / icons

• Flowchart and Sequence entries added to the quick-insert diagram section, with the insert handler creating diagram blocks of those types.
• Front-button diagram icon map extended. The flowchart icon already existed in muya's assets; the sequence icon was ported from the legacy muyajs pngicon set (packages/muyajs/lib/assets/pngicon/sequence/). No placeholder icons were needed — both are dedicated assets.
• Exported flowchart/sequence diagram divs are centered (exportStyle.css), matching the other diagram types.

Test coverage

• src/state/__tests__/diagramFlowchartSequence.spec.ts — flowchart/sequence fences parse into the right diagram block type and round-trip back to their fence; mermaid/plantuml/vega-lite still parse (no regression); sequenceTheme defaults to 'hand'.
• src/ui/paragraphQuickInsertMenu/__tests__/diagramMenuEntries.spec.ts — the quick-insert diagram section exposes flowchart + sequence entries (with icons) alongside the existing three.

drawSVG itself needs a real browser layout engine, so the SVG output isn't asserted in vitest (happy-dom); the parse + round-trip + option-plumbing paths are covered, consistent with how the existing diagram types are tested.

Verification (all green)

lint            ✓ 0 errors
lint:types      ✓
check-circular  ✓ no circular deps
test            ✓ 398 passed (46 files)
test:spec       ✓ 1347 passed (4 files) — conformance gate not regressed
vite build      ✓ flowchart.js + sequence bundle cleanly (chrome70 target)

🤖 Generated with Claude Code