Indented (4-space) code blocks were emitted by goldmark's default
renderer as plain `<pre><code>` without the `code-block-container`
wrapper that the JS `initMarkupCodeCopy` keys on. As a result, only
fenced code blocks received the copy button. Register
`ast.KindCodeBlock` with a renderer that produces the same wrapper as
the highlighting renderer so both syntaxes get the button.
Extends `TestMarkdownFencedCodeBlock` to assert the wrapper is emitted
for indented blocks (and that HTML inside is escaped).
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
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