A2uiMarkdownRenderer

How a Text draws its Markdown.

The default, Inline, is the parser-free subset markdownText describes: headings, emphasis, code spans, escapes -- and lists, tables, block quotes and fenced code passed through as the characters they are. That gap is a real one, and this seam is how a host closes it without giving up the rest of Text: a host that already ships a Markdown renderer hands it in here and keeps the style resolution, the caption variant and the leaf margin that Text would otherwise make it reimplement. a2ui-material3-markdown ships one, Material3MarkdownRenderer, for a host that has none and does not mind the parser it brings.

CompositionLocalProvider(
    LocalA2uiMarkdownRenderer provides A2uiMarkdownRenderer { source, style, color, modifier ->
        MyMarkdown(source, style = style, color = color, modifier = modifier)
    },
) { A2uiSurface(/* ... */) }

A composable rather than a String -> AnnotatedString, because the constructs the default lacks are the ones that cannot be spelled as spans: a table is a layout, not a string with styles on it. A formatter seam would have let a host swap the inline decoration and nothing else, which is not the gap.

What the seam hands over is the whole of the text's drawing and nothing more. The source is the agent's, unparsed and unbounded: the length cap and scan budget that keep Inline's parse from being made quadratic by its input are Inline's own, so an implementation that parses brings its own bound. The style and color are what Text resolved for the variant -- the caption's bodySmall and dimmed colour, and for body text Color.Unspecified, which means "the style's, and LocalContentColor through it" rather than no colour, so a Button's label keeps the button's colour; an implementation that ignores them draws captions the size of body text. The modifier already carries the leaf margin, and goes on the outermost thing drawn, as A2uiImageLoader's does.

The specification's exclusions -- no HTML, images, or live links -- are the implementation's to keep; nothing here can keep them on its behalf. Inline reduces a link to its label so an agent has no way to open a URL that bypasses openUrl and its user-gesture rule, and a host renderer that makes links tappable hands the agent exactly that.

Hand over the same instance every time. Text's call to Markdown is keyed on the renderer instance (#31), so one rebuilt on every recomposition of the scope providing it drops whatever it remembered each time -- Inline's parse, or a host renderer's layout state. A top-level val, or one built once and held, keeps it.