TUI: Markdown syntax rendered as raw text in assistant messages

Bug Description

Assistant text messages in the TUI display raw markdown syntax instead of formatted output. Literal **bold**, \inline code`, ----separators, and##` headers are printed as-is.

Expected Behavior

• bold → ANSI bold escape codes
• inline code → distinct color/background, backticks stripped
• code blocks → syntax highlighted (tree-sitter) or indented/boxed
• ---- → full-width divider character (─)
• ## Header → bold/colored, no leading #

Current Behavior

All markdown syntax appears literally in the terminal output.

Relevant Code

The TextPart component in packages/tui/src/routes/session/index.tsx (line ~1679) uses the <markdown> element from @opentui/core:

<markdown
  syntaxStyle={syntax()}
  streaming={true}
  internalBlockMode="top-level"
  content={props.part.text.trim()}
  tableOptions={{ style: "grid" }}
  conceal={ctx.conceal()}
  fg={theme.markdownText}
  bg={theme.background}
/>

The ReasoningPart (line ~1572) uses <code filetype="markdown"> for reasoning blocks.

It appears the <markdown> component from @opentui/core (v0.4.5) is not converting markdown syntax to ANSI-styled terminal output — the raw markdown passes through unformatted.

Environment

• opencode version: 1.18.5
• Terminal: iTerm2 on macOS
• @opentui/core version: 0.4.5

Notes

The project already has marked (v17.0.6) and marked-shiki (v1.2.1) in dependencies, which could be used as an alternative markdown-to-ANSI renderer if the @opentui/core <markdown> component is not intended to handle this.