fix: don't read Cloudflare's injected jsd script as a refusal

demonicscans.org turned JS detections on, so Cloudflare began injecting
/cdn-cgi/challenge-platform/scripts/jsd/main.js into ordinary 200 pages.
isInterstitial matched the bare /cdn-cgi/challenge-platform/ prefix, so
every real demonic series page became errChallengeHeld: two per pass
parked the Lane in the 15m refusal backoff while plain TLS was in fact
returning the full page (200, 133KB, 22 chapter anchors, verified live
2026-08-16).

Match the challenge orchestration path /cdn-cgi/challenge-platform/h/
instead — served only by the interstitial itself, stable across its
wording and locale.

backend/internal/latest/browser.go

@@ -250,11 +250,18 @@ func browserConnectionLost(ctx context.Context) bool {
 const challengePollInterval = 2 * time.Second
 
 // isInterstitial reports whether html is Cloudflare's challenge page rather
-// than the site's own. Matched on the challenge runtime's script path, which is
-// stable across the interstitial's wording and locale — the visible "Just a
+// than the site's own. Matched on the challenge orchestration path
+// (/cdn-cgi/challenge-platform/h/<b|g|x>/orchestrate/...), which is stable
+// across the interstitial's wording and locale — the visible "Just a
 // moment..." title is neither.
+//
+// The bare "/cdn-cgi/challenge-platform/" prefix is NOT enough: Cloudflare
+// injects /cdn-cgi/challenge-platform/scripts/jsd/main.js into ordinary 200
+// pages when JS detections are on, so matching the prefix declared every real
+// demonic page a refusal and parked that Lane in 15m backoff (observed
+// 2026-08-16, demonic turned detections on).
 func isInterstitial(html string) bool {
-	return strings.Contains(html, "/cdn-cgi/challenge-platform/")
+	return strings.Contains(html, "/cdn-cgi/challenge-platform/h/")
 }
 
 // run navigates to target and re-reads until done reports an answer, bounded by

backend/internal/latest/browser_test.go

@@ -117,6 +117,25 @@ func TestBrowserOnlyCoverURL(t *testing.T) {
 		})
 	}
 }
+
+// The jsd script is injected into ordinary 200 pages when a zone turns JS
+// detections on; only the orchestration path means the page itself is the
+// challenge. Conflating the two parked the demonic Lane in refusal backoff
+// while every fetch was in fact the real series page (observed 2026-08-16).
+func TestIsInterstitial(t *testing.T) {
+	if !isInterstitial(challengeFixture) {
+		t.Fatal("challenge page not detected as interstitial")
+	}
+	const jsdInjected = `<html><head><title>The Possessed Grappler</title>
+<script src="/cdn-cgi/challenge-platform/scripts/jsd/main.js"></script></head>
+<body><a  href="/chaptered.php?manga=13721&chapter=22">Chapter 22</a></body></html>`
+	if isInterstitial(jsdInjected) {
+		t.Fatal("real page carrying the injected jsd script misread as interstitial")
+	}
+	if got, ok := demonicLatestChapter("", jsdInjected); !ok || got.Label != "Chapter 22" {
+		t.Fatalf("demonicLatestChapter = %+v, ok = %v, want Chapter 22", got, ok)
+	}
+}
 func TestClassifyBrowserInterruption(t *testing.T) {
 	if err := classifyBrowserError(context.Background(), true, context.Canceled); !errors.Is(err, errBrowserInterrupted) {
 		t.Fatalf("classifyBrowserError(context.Canceled) = %v, want browser interruption", err)