[eric] browser: one safe capture helper; a half-ready webview no longer crashes the app

frontend/src/shared/captureBrowserShot.ts

@@ -0,0 +1,23 @@
+import { getWebview } from './browserRegistry';
+
+// One place for "get me a picture of a browser card, best effort". Four callers were hand-rolling
+// it and three got it wrong in a different way, because capturePage fails in two shapes: it THROWS
+// synchronously on a webview that is attached but not yet dom-ready (unguarded, that one took the
+// whole dashboard down through AgentCard's ErrorBoundary), and it never settles at all on a guest
+// the compositor is not drawing, so the timeout is not optional either.
+const DEFAULT_SHOT_TIMEOUT_MS = 1200;
+
+/** A data URL of the card's live page, or null. Never throws, never hangs. */
+export async function captureBrowserShot(browserId: string, timeoutMs: number = DEFAULT_SHOT_TIMEOUT_MS): Promise<string | null> {
+  try {
+    const wv = getWebview(browserId);
+    if (!wv?.capturePage) return null;
+    const image = await Promise.race([
+      wv.capturePage(),
+      new Promise<null>((resolve) => { window.setTimeout(() => resolve(null), timeoutMs); }),
+    ]);
+    return image && !image.isEmpty() ? image.toDataURL() : null;
+  } catch {
+    return null;
+  }
+}