TUI: streaming Markdown list items render with truncated content while raw is intact

Description

While the assistant is streaming a Markdown response, list-item contents get silently truncated in the TUI. The raw message stored in ~/.local/share/opencode/opencode.db (part table) is complete; only the rendered output is broken. Adjacent paragraphs render fine.

• No Code highlighting failed, falling back to plain text warning ever prints. The opencode process's fd 2 was verified redirected to tee and the resulting log stayed 0 bytes for the whole session.
• No exception in opencode.log either.
• Related but distinct: #38475 reports the same silent Markdown breakage class for fenced JSON code blocks. This one is list items with a mix of **bold** and `inline code`.

Raw markdown (from DB, verbatim):

インストール完了です。

## 修正内容

**`runCommand` を exec チャネル（PTY なし）ベースに書き直しました。**

- 以前は **PTY+shell チャネル**で `herdr pane list` を送り、プロンプトの終端を推測していたため、出力が確定せずハングしていました
- 今回は **exec チャネル**（`SSHChannelRequestEvent.ExecRequest`）でコマンドを実行するので、コマンド完了でチャネルが閉じ、出力が確実に確定します
- `runCommandOnConnection`（接続中の監視用）も同じ exec チャネル方式

これで、接続ボタン → herdr 一覧取得 → シート表示（または通常接続）が確実に動くはずです。

## 確認

1. 接続ボタンを押す → スピナー → herdr セッションのシートが出る、または通常接続される
2. 通常接続が復活したか

動作確認して、結果を教えてください。

Rendered in TUI (see screenshot):

• - 以前 — everything after 以前 dropped
• - 今回は exec チャネル ( ` — truncated at the opening backtick
• - ` — only the opening backtick, rest dropped
• 1. 接続ボタンを — rest dropped
• 2. 通常 — rest dropped

The two paragraphs and the H2 headings render fully. The bold+inline-code header line (**\runCommand` を exec ...) renders fully. The これで、接続ボタン → herdr ...` paragraph after the bullet list also renders fully.

Investigation notes

• Marked's lexer parses the same raw text into complete tokens (each list item's inline text / strong / codespan sequence is intact).
• Chunked-feed simulation (5 chars/chunk) into MarkdownRenderable with streaming: true — tried with both MockTreeSitterClient and the real markdown TreeSitterClient. Final rendered frame contains full content in both cases. Not reproducible outside the production binary this way.
• Likely path: CodeRenderable used for list-item text keeps its textBuffer at the initialStyledText snapshot (built at item-construction time from the inline tokens at that moment). Under real streaming timing where the highlight loop is repeatedly preempted before it can setStyledText, the buffer never advances.

Plugins

None.

OpenCode version

1.18.18

Steps to reproduce

Not reliably reproducible on demand. Happens sporadically while the assistant streams a Markdown response that contains list items mixing **bold** and `inline code`. The example above was captured mid-session in a long-running build task.

Screenshot and/or share link

Operating System

macOS 26.3.1 (Darwin 25.3.0), Apple Silicon.

Terminal

herdr (terminal multiplexer), running inside iTerm 2.