488d4384a1
Markus, Felix, and Nora independently flagged the {@html …} boundary as a
distributed-knowledge security risk: today renderBody and renderTranscriptionBody
return string, so the next refactor that does {@html block.text} (instead of
{@html renderBlockHtml(block)}) is one typo away from a stored-XSS regression.
Introduce a SafeHtml brand type (string with a phantom __brand) returned by
both renderers and by renderBlockHtml in TranscriptionReadView. Compile-time
enforcement of the escape invariant — costs zero runtime, makes the contract
auditable in one file.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>