feat(news): interaction seam for What's New (impression/open/link_click/video_play)

New lib/newsEvents.ts registry (same pattern as newsSource.ts): OSS
default is a no-op sink; an extension overlay can register one to
forward the signals to its own analytics. NewsAnnouncer reports the
toast impression and modal opens (toast vs Help menu); NewsMarkdown
grows an optional onInteract callback fired on body link clicks and
YouTube preview plays — the admin authoring preview passes nothing, so
authoring never counts as engagement.

frontend/src/components/layout/NewsAnnouncer.tsx

@@ -25,6 +25,7 @@ import { useEffect, useState } from 'react';
 import { createPortal } from 'react-dom';
 import { useTranslation } from 'react-i18next';
 import { getNextNews, type NewsPost } from '../../lib/newsSource';
+import { reportNewsEvent } from '../../lib/newsEvents';
 import { NewsMarkdown } from './NewsMarkdown';
 import { registerEditorCommand } from '../../lib/editorCommands';
 import './NewsAnnouncer.css';
@@ -46,6 +47,7 @@ export function NewsAnnouncer() {
         if (cancelled || !p) return;
         setPost(p);
         setToastVisible(true);
+        reportNewsEvent('impression', p.id);
       });
     }, FETCH_DELAY_MS);
     return () => {
@@ -62,6 +64,7 @@ export function NewsAnnouncer() {
     return registerEditorCommand('help.whatsNew', () => {
       setToastVisible(false);
       setExpanded(true);
+      reportNewsEvent('open', post.id, { via: 'menu' });
     });
   }, [post]);
 
@@ -101,7 +104,17 @@ export function NewsAnnouncer() {
             </button>
           </div>
           <div className="velxio-news-body">
-            <NewsMarkdown>{post.body_md}</NewsMarkdown>
+            <NewsMarkdown
+              onInteract={(kind, href) =>
+                reportNewsEvent(
+                  kind === 'video' ? 'video_play' : 'link_click',
+                  post.id,
+                  { href },
+                )
+              }
+            >
+              {post.body_md}
+            </NewsMarkdown>
           </div>
           <div className="velxio-news-footer">
             <button className="velxio-news-ok" onClick={() => setExpanded(false)}>
@@ -136,6 +149,7 @@ export function NewsAnnouncer() {
         className="velxio-news-toast-more"
         onClick={() => {
           setExpanded(true);
+          reportNewsEvent('open', post.id, { via: 'toast' });
         }}
       >
         {t('news.readMore', 'Read more')} →

frontend/src/components/layout/NewsMarkdown.tsx

@@ -17,6 +17,11 @@
  *     knowing the ![](…) syntax. An explicit [label](…png) stays a link.
  *   - All links open in a new tab (the modal sits on top of the editor;
  *     navigating away would lose workspace state).
+ *
+ * The optional `onInteract` callback fires when the reader clicks a link
+ * ('link') or starts a video preview ('video'). The announcement passes
+ * a handler wired to lib/newsEvents.ts; the admin preview passes nothing,
+ * so authoring never counts as engagement.
  */
 
 import { useState } from 'react';
@@ -37,7 +42,9 @@ function youTubeId(href: string): string | null {
   return m ? m[1] : null;
 }
 
-function YouTubePreview({ id }: { id: string }) {
+export type NewsInteractKind = 'link' | 'video';
+
+function YouTubePreview({ id, onPlay }: { id: string; onPlay?: () => void }) {
   const [playing, setPlaying] = useState(false);
   if (playing) {
     return (
@@ -55,7 +62,10 @@ function YouTubePreview({ id }: { id: string }) {
     <button
       type="button"
       className="velxio-news-video velxio-news-video-thumb"
-      onClick={() => setPlaying(true)}
+      onClick={() => {
+        setPlaying(true);
+        onPlay?.();
+      }}
       aria-label="Play video"
     >
       <img src={`https://i.ytimg.com/vi/${id}/hqdefault.jpg`} alt="Video preview" loading="lazy" />
@@ -64,7 +74,13 @@ function YouTubePreview({ id }: { id: string }) {
   );
 }
 
-export function NewsMarkdown({ children }: { children: string }) {
+export function NewsMarkdown({
+  children,
+  onInteract,
+}: {
+  children: string;
+  onInteract?: (kind: NewsInteractKind, href: string) => void;
+}) {
   return (
     <ReactMarkdown
       remarkPlugins={[remarkGfm]}
@@ -75,9 +91,19 @@ export function NewsMarkdown({ children }: { children: string }) {
           if (id) {
             return (
               <>
-                <YouTubePreview id={id} />
+                <YouTubePreview
+                  id={id}
+                  onPlay={href ? () => onInteract?.('video', href) : undefined}
+                />
                 {text && text !== href && (
-                  <a href={href} target="_blank" rel="noreferrer">{kids}</a>
+                  <a
+                    href={href}
+                    target="_blank"
+                    rel="noreferrer"
+                    onClick={() => href && onInteract?.('link', href)}
+                  >
+                    {kids}
+                  </a>
                 )}
               </>
             );
@@ -86,7 +112,14 @@ export function NewsMarkdown({ children }: { children: string }) {
             return <img src={href} alt="" loading="lazy" />;
           }
           return (
-            <a href={href} target="_blank" rel="noreferrer">{kids}</a>
+            <a
+              href={href}
+              target="_blank"
+              rel="noreferrer"
+              onClick={() => href && onInteract?.('link', href)}
+            >
+              {kids}
+            </a>
           );
         },
         img: ({ src, alt }) => (

frontend/src/lib/newsEvents.ts

@@ -0,0 +1,56 @@
+/**
+ * Product-news interaction sink ("What's New" telemetry seam).
+ *
+ * Same seam pattern as newsSource.ts / proSession.ts: OSS ships a no-op
+ * default and an extension overlay may register a sink that forwards the
+ * signals wherever it wants (velxio.dev sends them to its analytics
+ * pipeline). A pure OSS build never reports anything anywhere — the
+ * events below simply vanish.
+ *
+ * Event vocabulary (postId is always the news post's id):
+ *   - impression  → the corner toast rendered for the user
+ *   - open        → the full post modal was opened (detail.via:
+ *                   'toast' | 'menu')
+ *   - link_click  → a link inside the post body was clicked
+ *                   (detail.href)
+ *   - video_play  → a YouTube preview inside the body was started
+ *                   (detail.href)
+ */
+
+export type NewsEventKind = 'impression' | 'open' | 'link_click' | 'video_play';
+
+export interface NewsEventDetail {
+  /** Target URL for link_click / video_play. */
+  href?: string;
+  /** How the modal was opened for 'open'. */
+  via?: 'toast' | 'menu';
+}
+
+type NewsEventSink = (
+  kind: NewsEventKind,
+  postId: string,
+  detail?: NewsEventDetail,
+) => void;
+
+let _sink: NewsEventSink | null = null;
+
+export function registerNewsEventSink(sink: NewsEventSink): void {
+  _sink = sink;
+}
+
+/**
+ * Report a news interaction. Never throws — telemetry must not be able
+ * to break the announcement UI.
+ */
+export function reportNewsEvent(
+  kind: NewsEventKind,
+  postId: string,
+  detail?: NewsEventDetail,
+): void {
+  try {
+    _sink?.(kind, postId, detail);
+  } catch (err) {
+    // eslint-disable-next-line no-console
+    console.debug('[oss] news event sink failed:', err);
+  }
+}