Markdown renderer errors on [[double-bracket]] wikilink syntax in tool call output

Bug Description

Claude Code's terminal markdown renderer fails to handle an AST node when rendering bash tool call content that contains [[double-bracket]] wikilink syntax. The error message Unhandled node type: string appears between Claude's output text and the permission prompt.

Reproduction

Any bash tool call whose command text contains [[double-bracket]] wikilink syntax triggers the error. For example, a heredoc writing Obsidian-style markdown with [[wikilinks]]:

obs_put "Page Name" "$(cat <<'PAGEEOF'
## Sources
- [[Gemma]] — Google DeepMind open-weight model family
- [[Qwen3-TTS]] — Alibaba/Qwen open-weight speech synthesis family
- [[vLLM]] — high-throughput inference engine
PAGEEOF
)"

Expected Behavior

The tool call content should render without errors.

Actual Behavior

The message Unhandled node type: string is displayed between the rendered output and the "Do you want to proceed?" permission prompt.

Screenshot

!Screenshot showing the error

Note: Screenshot available but cannot be uploaded via CLI. The error Unhandled node type: string appears directly after rendered markdown containing [[wikilink]] syntax, just before the permission prompt.

Impact

Cosmetic only — tool execution is not affected, writes succeed. But the error message is confusing and clutters the output.

Environment

• Claude Code CLI (Linux)
• Triggered by CommonMark renderer encountering non-standard [[...]] markdown syntax in tool call output