The quick-reply box built its body with appendPlainTextSignature, which runs
the identity's HTML signature through htmlToPlainText, and sent a text-only
message (htmlBody was undefined). A formatted signature (e.g. <strong>…) was
therefore flattened to plain text in the sent mail, even though it previewed
correctly in the identity editor. The full composer already builds an HTML
signature block; quick reply did not.
Add an appendHtmlSignature helper (mirrors the composer's send-time block) and,
when the sending identity has an HTML signature, send a matching HTML body from
handleQuickReply so the markup is preserved. Text-only identities keep the
plain-text-only behavior.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
