Every .md preview renders through MarkdownDocument (htmlInfo is ungated),
but its markdown segments passed the raw source into MarkdownText, whose
chat-security stance drops non-http(s) image destinations — so local
markdown-syntax images (, reference-style definitions)
always fell back to alt text. Only HTML <img src> tags were rewritten
(postProcessSanitized).
Apply rewriteLocalImageUrls to each markdown run (segment + appended
reference definitions) inside MarkdownDocument's prepared memo, through
the same media trust fence the sanitized HTML leaves already use.
Idempotent for already-absolute media URLs; remote destinations
untouched. Also correct the stale "non-null only for HTML documents"
comment on TextEditor's htmlInfo.