feat(opentui-v2): Phase 2b-ii — native markdown for assistant text (Phase 2 done)

Assistant text parts now render through the NATIVE markdown renderable instead of
plain spans — bold/headings/lists/fences render, raw `**`/backtick markup is
concealed (spec §7; never hand-roll a parser).

- view/markdown.tsx: `<code filetype="markdown" streaming conceal drawUnstyledText>`
  (CodeRenderable — opencode's v2 AssistantText path; `<markdown>` +
  internalBlockMode="top-level" deferred paint headlessly). SyntaxStyle.fromStyles
  is derived from the theme (markup.* → theme.color.*, non-hex colors guarded) and
  cached by theme-object identity so all text parts share one instance, rebuilt
  only on skin change. drawUnstyledText paints raw text immediately while
  Tree-sitter highlighting settles (and makes it headless-capturable).
- view/messageLine.tsx: text-part Match renders <Markdown> instead of <text>.
- test/lib/render.ts: settle async markdown via flush(); captureFrame gains an
  `until` option (waitForFrame) for content that paints after the first pass.

Verified: bun run check green (23 tests / 5 files). Live tmux: a markdown reply
(heading + bold word + 2-item list) rendered with `**` concealed (grep -c '**' = 0);
Ctrl+C clean, no orphan. Phase 2 complete (2a shell + 2b-i parts/tools + 2b-ii
markdown) — smoke steps 1–4 run live. Next: Phase 3 blocking prompts.

ui-tui-opentui-v2/src/test/render.test.tsx

@@ -29,7 +29,7 @@ describe('App render (Phase 1, themed)', () => {
           <App store={store} />
         </ThemeProvider>
       ),
-      { width: 60, height: 16 }
+      { until: 'Hi there, glitch!', width: 60, height: 16 }
     )
 
     expect(frame).toContain('Hermes Agent') // default brand.name
@@ -74,7 +74,7 @@ describe('App render (Phase 1, themed)', () => {
           <App store={store} />
         </ThemeProvider>
       ),
-      { width: 60, height: 16 }
+      { until: 'Listing files:', width: 60, height: 16 }
     )
 
     expect(frame).toContain('Listing files:') // text part

ui-tui-opentui-v2/src/view/markdown.tsx

@@ -0,0 +1,67 @@
+/**
+ * Markdown — assistant/reasoning text rendered with the NATIVE renderable, never
+ * a hand-rolled parser (spec v4 §7). Uses `<code filetype="markdown" streaming>`
+ * (`CodeRenderable`) — opencode's v2 text path (`session-v2.tsx:358` AssistantText)
+ * — backed by the same markdown tokenizer + Tree-sitter as `<markdown>`, but it
+ * paints reliably (incl. headless): `drawUnstyledText` draws the raw text
+ * immediately while highlighting settles, `conceal` hides the `**`/backtick
+ * markers, `streaming` feeds incremental deltas.
+ *
+ * The `SyntaxStyle` is derived from the active theme (no hardcoded styles — §7.5)
+ * and cached by theme-object identity, so all text parts share ONE instance and
+ * it's rebuilt only when the skin changes (a new `Theme` object).
+ */
+import { RGBA, SyntaxStyle } from '@opentui/core'
+
+import type { Theme } from '../logic/theme.ts'
+import { useTheme } from './theme.tsx'
+
+const FALLBACK = RGBA.fromHex('#E6EDF3')
+const HEX6 = /^#[0-9a-fA-F]{6}$/
+
+/** Theme colors are usually hex but may be `ansi256(n)`/`rgb(...)` after light-mode
+ *  normalization — only hand hex to RGBA.fromHex, else fall back. */
+function rgba(color: string): RGBA {
+  return HEX6.test(color) ? RGBA.fromHex(color) : FALLBACK
+}
+
+function buildSyntaxStyle(theme: Theme): SyntaxStyle {
+  const c = theme.color
+  return SyntaxStyle.fromStyles({
+    default: { fg: rgba(c.text) },
+    'markup.heading': { bold: true, fg: rgba(c.primary) },
+    'markup.heading.1': { bold: true, fg: rgba(c.primary) },
+    'markup.heading.2': { bold: true, fg: rgba(c.accent) },
+    'markup.heading.3': { bold: true, fg: rgba(c.accent) },
+    'markup.bold': { bold: true, fg: rgba(c.text) },
+    'markup.italic': { fg: rgba(c.text), italic: true },
+    'markup.list': { fg: rgba(c.accent) },
+    'markup.quote': { fg: rgba(c.muted) },
+    'markup.link': { fg: rgba(c.accent) },
+    'markup.raw': { fg: rgba(c.label) },
+    'markup.raw.block': { fg: rgba(c.label) }
+  })
+}
+
+let cache: { theme: Theme; style: SyntaxStyle } | undefined
+function syntaxStyleFor(theme: Theme): SyntaxStyle {
+  if (cache && cache.theme === theme) return cache.style
+  const style = buildSyntaxStyle(theme)
+  cache = { style, theme }
+  return style
+}
+
+export function Markdown(props: { text: string; streaming?: boolean }) {
+  const theme = useTheme()
+  return (
+    <code
+      filetype="markdown"
+      content={props.text}
+      syntaxStyle={syntaxStyleFor(theme())}
+      streaming={props.streaming ?? false}
+      drawUnstyledText
+      conceal
+      fg={theme().color.text}
+    />
+  )
+}

ui-tui-opentui-v2/src/view/messageLine.tsx

@@ -11,6 +11,7 @@
 import { For, Match, Show, Switch } from 'solid-js'
 
 import type { Message } from '../logic/store.ts'
+import { Markdown } from './markdown.tsx'
 import { useTheme } from './theme.tsx'
 import { ToolPart } from './toolPart.tsx'
 
@@ -52,11 +53,7 @@ export function MessageLine(props: { message: Message }) {
                   )}
                 </Match>
                 <Match when={part.type === 'text' && part}>
-                  {t => (
-                    <text>
-                      <span style={{ fg: theme().color.text }}>{t().text}</span>
-                    </text>
-                  )}
+                  {t => <Markdown text={t().text} streaming={m().streaming ?? false} />}
                 </Match>
               </Switch>
             )}