Artifacts containing mermaid diagrams cannot be shared publicly

Environment

• Claude Code 2.1.197 (desktop app, macOS)
• Individual (non-Team/Enterprise) account

Description

Publishing an artifact that contains a mermaid block (a ``` `mermaid `` fence in markdown or <pre class="mermaid">` in HTML) succeeds, and the diagram renders correctly for the owner. However, the artifact can't be shared: in the Share dialog, changing General access from "Only you" fails with "This version can't be shared publicly. Publish a new version or change the shared version, then try again." and the "Shared version" dropdown is disabled. Republishing new versions doesn't help while the mermaid block remains.

This is confusing because the Artifact tool's own guidance steers Claude toward mermaid ("Artifacts render mermaid diagrams natively... no external libraries involved"), so Claude reaches for it by default, silently producing unshareable artifacts. Nothing in the UI or docs connects the sharing error to the diagram.

Steps to reproduce

1. In Claude Code, have Claude publish an artifact whose HTML contains only:

``html
<h1>Test</h1>
<pre class="mermaid">
graph TD
A --> B
</pre>
``

1. Open the published artifact and its Share dialog.
2. Try to change General access to "Anyone with the link".

Expected: artifact can be shared, or the error explains what content is blocking sharing.

Actual: "This version can't be shared publicly..." with the version dropdown disabled.

Removing the mermaid block and republishing (same content otherwise) makes sharing work immediately. Bisected from a larger document: prose, external links, tables, and JSON code blocks all share fine; only the mermaid block triggers the error.