Agentic Mermaid Live Editor Development

Agentic Mermaid live editor development

Edit the modular editor sources and preserve the contracts shared by the standalone editor and the deployed website.

Source map

Do not edit generated editor.html or website/public/ files directly.

Build and test cycle

Run the target that owns the changed surface:

bun run editor          # standalone editor.html
bun run website         # production website/public, including /editor/
bun run website:check   # clean in-memory website + Worker artifact contracts
bun run typecheck

For behavior changes, also run the focused editor unit tests and the browser lane. The browser lane requires Playwright Chromium and AM_BROWSER_TESTS=1.

State contract

Keep editor state in the canonical shape from editor/js/state.js:

state = {
  palette: 'paper',
  style: 'crisp',
  seed: 0,
  zoom: 1,
  config: {},
}

• palette stores the registered palette input name.
• style stores the registered Look input name or crisp.
• seed affects styled ink without changing layout.
• config contains admitted serializable render options.
• Browser chrome dark/light mode is separate from diagram appearance and must not rewrite state.palette.

When adding state, update serialization, sanitization, restoration, control hydration, and tests together.

Render and verification boundary

Follow the pipeline in editor/js/rendering.js:

editor input
  -> scheduleRender()
  -> doRender()
  -> buildOptions()
  -> renderMermaidSVGWithReceipt()
  -> verifyNoExternalRefs()
  -> insertStrictRenderedSvg()
  -> verifyMermaid()
  -> retain the receipt-bearing artifact only when verification succeeds

Keep security: "strict" and embedFontImport: false host-owned. Admit restored configuration through SHARED_RENDER_OPTION_FIELDS and validateSerializableRenderOptions; never trust hash or storage data directly. Insert one parsed SVG node with replaceChildren, not arbitrary shared HTML.

Do not enable share or export actions from stale DOM. Require the current source, receipt digests, verified artifact, and preview SVG to agree.

URL sharing contract

Treat the URL payload as a versioned producer/consumer boundary. The canonical state is:

{
  source: string
  palette?: string
  style?: string
  seed?: number
  config?: Record<string, unknown>
}

The hash codec is:

deflate:<base64url(deflate-raw(UTF-8(JSON(state))))>

Use editor/js/sharing.js as the browser source of truth. For Node/build-time links, import editorStateHref() or hostedEditorStateHref() from scripts/site/editor-state-url.ts. Never hand-roll base64, compression, field names, or /editor/ URL assembly in another producer.

Keep these behaviors:

• Reject unknown fields such as the removed theme alias.
• Bound encoded and decoded bytes.
• Fail closed on corrupt, unsupported, or oversized hashes.
• Do not restore a draft, query example, or plausible default after hash decode failure.
• Use ?example=<id> only for canonical editor examples; use a state hash for source/config/style snapshots.
• Update the hash only after a current render verifies successfully.

When changing this contract, update the browser codec, build-time codec, every producer, checked-in deep links, and both unit and real-navigation tests in the same change.

Configuration controls

For an existing render option:

1. Add accessible controls in editor/html/left-panel.html or the relevant partial.
2. Store UI state in editor/js/config-panel.js.
3. Include the value in readConfig() and restore it in hydrateConfigControls().
4. Keep state.config serializable and admitted by the shared render-options schema.
5. Render through buildOptions(); do not patch the preview into a state the renderer cannot reproduce.

For new public options, update the library contract first, then the editor. Do not create an editor-only alias.

Examples

Add or edit examples in editor/examples.ts. Preserve stable IDs because /editor/?example=<id>, the sidebar, website examples, and tests depend on them. Examples may supply source and admitted config; loading one must preserve the user-selected Palette unless the URL snapshot explicitly carries a palette.

Export behavior

Keep SVG, PNG, ASCII, and Unicode exports derived from current receipt-bearing artifacts. Preserve strict SVG verification and self-hosted font handling. PNG scale changes output dimensions; it must not change diagram semantics or silently fall back after an error.

Regression gates

Use these tests when touching editor links or state:

bun test src/__tests__/editor-link-contract.test.ts
bun test src/__tests__/editor-security-closures.test.ts
bun test src/__tests__/website-build.test.ts
AM_BROWSER_TESTS=1 bun test src/__tests__/website-browser-a11y.test.ts --timeout 600000

The repository-wide link contract must decode every checked-in hosted editor deep link. The website build contract must decode every generated HTML/JSON editor-state link and reject legacy hashes or unknown fields. The browser test must navigate from a real public page into the editor and verify that initialization preserves the hash and source.

Common pitfalls

• Updating a decoder without migrating every producer.
• Updating unit fixtures to the new codec while leaving public links untouched.
• Reintroducing theme where the editor state contract requires palette.
• Testing the editor only with hashes manufactured inside the editor test suite.
• Editing generated outputs instead of modular sources.
• Letting dark/light chrome mutate diagram appearance.
• Restoring drafts after a broken share URL, which can make unrelated local content look shared.
• Enabling copy/export from a stale or unverified preview.