fix(cli): reject blocked website captures

packages/cli/src/capture/pageBlockDetection.ts

@@ -0,0 +1,34 @@
+export interface PageLoadEvidence {
+  httpStatus: number | null;
+  title: string;
+  textLength: number;
+  bodyChildCount: number;
+  hasChallengeElement: boolean;
+}
+
+/**
+ * Returns an actionable failure only for strong protection-page signals.
+ * Low text by itself is intentionally not fatal because image-led sites and
+ * client-rendered applications can legitimately have very little body copy.
+ */
+export function detectBlockedPage(evidence: PageLoadEvidence): string | undefined {
+  const isMinimalDom = evidence.bodyChildCount <= 5 && evidence.textLength < 500;
+  const hasBlockedStatus =
+    evidence.httpStatus === 401 || evidence.httpStatus === 403 || evidence.httpStatus === 429;
+  const hasBlockedTitle =
+    /^(?:error\s*)?(?:401|403|429)(?:\s*[-:—]\s*|\s+)|forbidden|access denied|attention required|just a moment/i.test(
+      evidence.title,
+    );
+
+  if (!isMinimalDom || (!evidence.hasChallengeElement && !hasBlockedStatus && !hasBlockedTitle)) {
+    return undefined;
+  }
+
+  const statusDetail =
+    evidence.httpStatus === null ? "no HTTP status" : `HTTP ${evidence.httpStatus}`;
+  return (
+    `Website capture blocked: the loaded page matched an access-protection response ` +
+    `(${statusDetail}, title ${JSON.stringify(evidence.title)}, ${evidence.textLength} text chars). ` +
+    "The site may reject automated or data-center traffic; retry from an allowed network or provide source assets directly."
+  );
+}