Chat: render markdown in messages, matching the website #3468

Mobile chat renders message bodies as plain text. ThreadMessageItem.tsx puts the body in a bare <Text> via renderTextWithBoldMentions, which does linkify, emoji and bold @mentions and nothing else. Web renders the same messages as markdown, so formatting a message on desktop and reading it on mobile shows raw ** and backticks.

What web does

features/chat/hooks/use-message-rendering.tsx runs simpleMarkdownToHTML from @ecency/render-helper, sanitizes with DOMPurify, and renders Ecency post links through a dedicated card component.

Scope

Use the same simpleMarkdownToHTML so both clients share one definition of what chat markdown means, and render the result with react-native-render-html. Both are already dependencies (@ecency/render-helper ^2.5.23, react-native-render-html ^6.3.4), so no new packages.

Deliberately simpleMarkdownToHTML and not the full post renderer in postParser.tsx: chat is a lighter subset and should not diverge from web.

Must not regress

The existing chat rendering does several things the markdown path has to keep:

• linkify, including the Ecency profile link shortening in setLinkText
• emoji substitution via emojifyMessage
• bold @mentions with the tap-to-open-profile behaviour
• image extraction in parseMessageContent (images are pulled out of the body and rendered separately)
• the tap targets and long-press actions on the message row

Worth checking during implementation

• Angle brackets get eaten. Once a body goes through an HTML renderer, literal <user> in a message is parsed as an unknown tag and disappears. The moderation bot posts help text containing !ban <user> [30d], so this is a live case, not hypothetical.
• Sanitization. react-native-render-html will not execute scripts, but the allowed tag and attribute set should still be constrained rather than left at the default.
• List performance. Chat threads are long and virtualized; per-message HTML parsing is heavier than a <Text>. Worth measuring on a long channel before and after, and memoizing per message id.

Related: the moderation commands in ecency/vision-web#1380 currently reply in plain text specifically because this renderer does not exist yet.