Rich message rendering

Contract between the Liminal harness (what the model may emit) and each UI shell (what users actually see).

Harness output

The harness streams assistant text on the text channel (channel: "assistant"). The system prompt (packages/tools/src/systemPrompt.ts) encourages:

Format	Use case
GFM markdown	Prose, tables, task lists, > [!NOTE] callouts, fenced code
Raw HTML	Gradient cards, flex layouts, KPI blocks, “Bottom line” panels
```html fences	Same as raw HTML; preferred for large blocks; streams live on web/desktop
Images	 or data:image/…
Video	Bare YouTube/Vimeo URLs or links
User attachments	```attached_images block (vision workflow) + generic files via composer (see Compose dock & attachments)

Tool rows, harness trace, and working-state snapshots are not rich-rendered.

Persistent desktop widgets (weather panels, calculators, live dashboards) are not chat HTML — the agent uses spawn_app and separate OS windows. See Liminal desktop apps.

Web UI (reference)

Implementation: packages/web/client/liminalMarkdown.tsx, App.tsx assistant case.

• GFM via remark-gfm
• Inline HTML via rehype-raw + rehype-sanitize
• Fenced HTML via HtmlEmbedBlock + streaming fence split (liminalMarkdownUtils.ts)
• Prism for code fences; html/htm/xhtml fences → live HTML
• Custom img, YouTube/Vimeo iframes, alert blockquotes

Desktop UI

Implementation: apps/liminal_desktop/lib/ui/rich_message/.

Capability	Desktop
GFM	flutter_markdown + ExtensionSet.gitHubWeb
Fenced HTML	HtmlEmbedView (WebView, JS off, sanitized)
Inline HTML	flutter_widget_from_html (sanitized)
Code fences	flutter_highlight (non-html langs)
Images	https:, data:image/*, workspace /media?path=
Video	YouTube/Vimeo embed WebView
User image attach	send_message.attachments → same wire block as web
Streaming HTML fence	Dart port of extractStreamingHtmlFence

Security

• No arbitrary JavaScript in assistant HTML embeds
• Block file://, javascript:, blob: in untrusted URLs
• Workspace media only via sidecar GET /media (path under chat workspace root, token-gated)
• Size caps aligned with DEFAULT_IMAGE_ATTACHMENT_LIMITS

Versioning

Render contract changes should update this doc and keep web + desktop in sync. Shared TS utils live in liminalMarkdownUtils.ts; Dart port in liminal_markdown_utils.dart.