[A-PachecoT]

Summary

• Fixes end-of-stream heading shrink regression: h2 "Estimación rápida" (and any other heading) collapsed from 1.35em to browser default ~21px the moment the stream finished.
• Root cause: Message.tsx swapped from <StreamingMarkdown> (inline BLOCK_STYLES with fontSize: 1.35em on h2) to <MessageContent> (which relies on Tailwind prose class). @tailwindcss/typography is not installed in consuming apps (TimelyAI / Landing / InboxAI) — so prose is a no-op and headings fall back to the browser default.
• Fix: render <StreamingMarkdown> for all assistant messages and toggle the isStreaming prop based on isStreamingThis. User messages still use <MessageContent> (user input rarely has markdown).

Before / after

Before: during stream → <StreamingMarkdown> with cf-stream-root cf-stream-active, h2 inline-styled 1.35em. Stream finishes → component swaps to <MessageContent> which renders <h2>Estimación rápida</h2> with only the prose class. prose resolves to nothing (plugin not installed) → h2 reverts to UA default (~21px / 1.5em bold) → visible shrink.

After: during stream → same. Stream finishes → same component stays mounted; only .cf-stream-active class drops. h2 keeps its inline fontSize: 1.35em, char spans freeze in place. Zero layout shift, zero size change.

- {isStreamingThis ? (
-   <StreamingMarkdown content={message.content} isStreaming isUser={isUser} />
- ) : (
-   <MessageContent content={message.content} format=\"markdown\" isUser={isUser} />
- )}
+ {message.role === \"assistant\" ? (
+   <StreamingMarkdown content={message.content} isStreaming={isStreamingThis} isUser={isUser} />
+ ) : (
+   <MessageContent content={message.content} format=\"markdown\" isUser={isUser} />
+ )}

Why not install @tailwindcss/typography?

That's a bigger change touching every consumer's tailwind config and potentially clashing with brand styles. The StreamingMarkdown inline BLOCK_STYLES are already the canonical rendering for streamed assistant output — we just keep using them post-stream too. Cheap, surgical, behavior-preserving.

Files

• src/components/chat-widget/Message.tsx — single-branch swap
• src/__tests__/components/Message.streaming.test.tsx — 4 tests rewritten around the new contract (StreamingMarkdown stays mounted; only cf-stream-active toggles)
• package.json — 0.5.2 → 0.5.3
• CHANGELOG.md — [0.5.3] entry

Test plan

• npx tsc --noEmit — clean (no new TS errors)
• npx vitest run src/__tests__/components/Message.streaming.test.tsx src/__tests__/components/StreamingMarkdown.debug.test.tsx — 8/8 pass
• After Cloudflare auto-deploy of Storybook (ui.cofoundy.dev), curl https://ui.cofoundy.dev/iframe.html?id=chat-message--streaming-finished&viewMode=story and grep for font-size:1.35em in the h2 attribute — should be present (was absent before this fix)
• Visual check in Chromatic: Chat/Message → Streaming Finished should look identical to Streaming Chunky mid-stream w.r.t. heading size

Out of scope

• StreamingMarkdown.tsx, useStreamingDrip.ts, streaming CSS — unchanged (already correct)
• @tailwindcss/typography install — deliberately deferred