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Claude Code Issues / #68834

[BUG] AskUserQuestion preview pane renders blank when content starts with an HTML-block tag (XML / HTML / SVG / Vue SFC)

Resolved 💬 1 comment Opened Jun 16, 2026 by skatset Closed Jul 12, 2026

Preflight Checklist

  • [x] I have searched existing issues and this hasn't been reported (only adjacent/different bugs exist — see References)
  • [x] This is a single bug report
  • [x] I am using the latest version of Claude Code

What's Wrong?

When AskUserQuestion is invoked with options that include a preview field, the right-hand preview pane renders completely blank if the preview content begins with an HTML / XML / SVG / Vue-SFC opening tag. The empty pane gives no indication that anything was supposed to be shown — the user just sees a blank panel and has to guess what they're choosing between.

The trigger is purely textual: it does not depend on the terminal (reproduced cross-platform per the closed-as-duplicate chain), and it does not depend on the amount of content (a 10-line XML reproduces it just as reliably as a 100-line one).

Reproducible Pattern (Empirically Verified)

I ran the same AskUserQuestion with 4 then 4-then-1 preview variants. Result is consistent:

| preview content begins with | Renders? |
|---|---|
| <config>... (XML) | Blank |
| <!DOCTYPE html>... (HTML) | Blank |
| <svg ...>... (SVG) | Blank |
| <template>... (Vue SFC) | Blank |
| def process_session(... (Python) | OK |
| # Heading... (Markdown) | OK |
| import { useState }... (JSX — angle brackets appear later, inside JS) | OK |
| interface SessionStore<...> (TS with generics) | OK |
| Plain prose | OK |

The breaking inputs all share one property: the first non-whitespace token is an HTML/XML tag opener. The working inputs all share the opposite property — the first line is regular code/prose, even if <...> appears later.

Workaround (Confirmed Working)

Wrapping the same content in a fenced code block fixes the rendering for every format above:

````

<config>
  ...
</config>

````

Same for ` `html , `svg , `vue `. Once wrapped, the pane renders normally. This is currently the only way I've found to keep markup-as-preview usable.

This is relevant to superpowers / brainstorming skill authors and anyone who calls AskUserQuestion with side-by-side previews of XML configs, SVG sketches, HTML mockups, or Vue/Svelte/Astro SFCs — until a fix ships, please pre-wrap these previews in a language-tagged fenced code block.

Root Cause Hypothesis (with evidence)

The Claude Code CLI bundles a CommonMark parser. strings on the binary (claude-code 2.1.153) surfaces a contiguous block of parser-option names:

hardSoftBreaks  wikiLinks  latexMath  collapseWhitespace
permissiveAtxHeaders  noIndentedCodeBlocks
noHtmlBlocks  noHtmlSpans  tagFilter

noHtmlBlocks existing as an option means HTML blocks are recognized by default. Per the CommonMark spec, §4.6 HTML blocks, a line beginning with <svg, <config, <template>, or <!DOCTYPE opens an HTML block — and the whole document up to the closing condition becomes a single raw-HTML AST node.

The terminal/Ink renderer downstream of the parser has no rule for displaying arbitrary raw HTML in a TUI, so the AST node is either passed through tagFilter-style sanitization to nothing, or simply skipped by the visitor that walks the tree. Either way: empty pane.

This neatly explains the binary outcome we observe — the bug fires iff CommonMark would have classified the first line as an HTML-block opener.

Suggested Fixes (in order of preference)

  1. Best — disable HTML-block parsing for AskUserQuestion previews. Previews are not a place where raw HTML should ever be honored (no browser, no XSS surface; the renderer can't render HTML anyway). Pass noHtmlBlocks: true (or equivalent) to the parser specifically when rendering the preview pane. Markup content then renders as plain paragraphs — verbatim, readable, exactly what users want.
  1. Add an explicit render rule for HtmlBlock nodes. Visit the node and print its raw source. This is the most conservative fix (no parser changes) but slightly more code: a single visitor case. Has the side benefit of also fixing the "looks like HTML but isn't valid markup" case.
  1. Detect the leading < and route through a code-block code path. Heuristic. Cheapest to ship but most likely to regress something. Listed for completeness; (1) is strictly better.

The author-side workaround (wrap in fenced code block) is a band-aid — skill authors and SDK consumers shouldn't need to know about CommonMark's HTML-block rule to make their previews show up.

Steps to Reproduce

  1. Invoke AskUserQuestion with at least one option whose preview field begins with <config>, <svg ...>, <template>, or <!DOCTYPE html>. Other options can be plain prose.
  2. Observe: the affected option's preview pane is blank. Plain-prose options render normally.
  3. Re-invoke the same call with the markup wrapped in ` `xml (or html/svg/vue`). The pane now renders.

Environment

  • Claude Code version: 2.1.153 (Homebrew cask claude-code)
  • OS: macOS 26 (Darwin 24.6.0), arm64
  • Terminal: kitty (also confirmed by cross-platform reporters in the closed-as-duplicate chain — Windows Terminal, VS Code, iTerm — so this is renderer-side, not terminal-specific)
  • Claude Model: Opus 4.7 (1M context)

Is this a regression?

Unknown — the AskUserQuestion preview pane has had a chain of rendering bugs (#38674, #33062, #65894). It is plausible this has been present since the side-by-side preview was introduced and was simply masked by the other rendering issues.

References

  • #38674 — preview pane truncation, repeatedly auto-closed as duplicate of unrelated iOS issue; demonstrates the "preview features get lost in dup-bot chains" pattern. Please do not auto-close this as duplicate of #38674 — it's a different rendering failure mode (blank, not truncation).
  • #33062 — also about preview pane (truncation, code-block content). Closed-as-duplicate by bot.
  • #65894 — open: separate preview-related bug (n+Enter drops highlighted option). Confirms the side-by-side preview surface is brittle.
  • #1150 — different layer (model-side <error> → <e> collapse on file reads), but adjacent symptom that searches surface; included for context.

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