Inline previews

When the user should see an HTML demo or a Markdown document inline in the assistant message, write (or update) a source-relative file, then emit this message directive as its own block (not inside a fenced code block):

::inline-vis{file="demo.html"}
::inline-vis{file="notes.md"}

Omitting source defaults to the workspace. Explicit source="workspace" is equivalent. For a read-only thread-storage artifact, write the document to $BB_THREAD_STORAGE/reports/result.html, then emit its storage-relative path:

::inline-vis{source="thread-storage" file="reports/result.html"}

Rules

• source is optional and must be workspace or thread-storage.
• file is relative to the selected source (e.g. demo.html, charts/out.html, notes.md). Workspace paths are relative to the current workspace; thread-storage paths are relative to $BB_THREAD_STORAGE. Never put an absolute path in the directive.
• height is optional and sets the preview height in pixels. It must be a whole number from 120 through 1200; omit it for the 224px default.
• .html, .htm, .md, and .markdown files are accepted.
• Inline and external CSS/JavaScript are supported in HTML. Remote images, fonts, media, fetches, and WebSockets are also allowed subject to normal browser CORS, mixed-content, and remote-server policies. Scripts execute in an opaque-origin iframe and cannot access the bb page, cookies, or storage. Markdown uses BB's renderer with sanitized HTML support.
• Keep files small (under the sidebar preview's 5 MiB document limit).
• Emit the directive only after the file exists on disk in the selected source.
• Prefer thread-storage for read-only generated reports and other artifacts that should not modify the workspace.
• Do not put the directive inside backticks or a markdown code fence, or it stays literal text.
• Incomplete streaming syntax stays literal until the closing } arrives — emit a complete directive in one piece when possible.

The bb app replaces the directive with an inline preview. If the plugin is disabled or the path is invalid, users see the original directive source or an inline error from the plugin.