diff --git a/packages/studio/src/hooks/useSlideshowTabState.test.ts b/packages/studio/src/hooks/useSlideshowTabState.test.ts
index 7aed27cc7..be45f448b 100644
--- a/packages/studio/src/hooks/useSlideshowTabState.test.ts
+++ b/packages/studio/src/hooks/useSlideshowTabState.test.ts
@@ -69,6 +69,13 @@ describe("useSlideshowTabState", () => {
harness.unmount();
});
+ it("still detects a malformed island — presence-only, not full manifest validation", () => {
+ const malformed = ``;
+ const harness = renderHook({ editingFileContent: malformed, rightPanelTab: "design" });
+ expect(harness.getState().isSlideshowComposition).toBe(true);
+ harness.unmount();
+ });
+
it("bounces rightPanelTab off 'slideshow' to 'renders' on a non-slideshow composition", () => {
const harness = renderHook({ editingFileContent: PLAIN_HTML, rightPanelTab: "slideshow" });
expect(harness.setRightPanelTabCalls).toEqual(["renders"]);
diff --git a/packages/studio/src/hooks/useSlideshowTabState.ts b/packages/studio/src/hooks/useSlideshowTabState.ts
index 5e38d6ba3..df7d49ea6 100644
--- a/packages/studio/src/hooks/useSlideshowTabState.ts
+++ b/packages/studio/src/hooks/useSlideshowTabState.ts
@@ -1,5 +1,5 @@
import { useEffect, useMemo, type MutableRefObject } from "react";
-import { slideshowIslandRegex } from "@hyperframes/core/slideshow";
+import { SLIDESHOW_ISLAND_TYPE, slideshowIslandRegex } from "@hyperframes/core/slideshow";
import type { SceneInfo } from "../components/panels/SlideshowPanel";
import type { IframeWindow } from "../player/lib/playbackTypes";
import type { RightPanelTab } from "../utils/studioHelpers";
@@ -27,11 +27,13 @@ export function useSlideshowTabState(params: {
// Presence-only (not full manifest validation): a malformed island should
// still surface the Slideshow tab so the user can see/fix it, rather than
- // making the whole panel disappear.
- const isSlideshowComposition = useMemo(
- () => Boolean(editingFileContent && slideshowIslandRegex("i").test(editingFileContent)),
- [editingFileContent],
- );
+ // making the whole panel disappear. The plain substring check short-circuits
+ // the regex scan on every non-slideshow file (the common case) without
+ // paying for a full-content RegExp pass.
+ const isSlideshowComposition = useMemo(() => {
+ if (!editingFileContent || !editingFileContent.includes(SLIDESHOW_ISLAND_TYPE)) return false;
+ return slideshowIslandRegex("i").test(editingFileContent);
+ }, [editingFileContent]);
// Derive scene list from the live clip manifest in the preview iframe.
const slideshowScenes = useMemo(() => {