fix(studio): hide the Slideshow tab and panel for non-slideshow compositions

The Slideshow tab rendered unconditionally, showing the branching editor
for any composition regardless of whether it was actually a slideshow —
a plain video comp offered a tab with nothing meaningful to edit.

Gate it on the composition carrying the slideshow JSON island
(<script type="application/hyperframes-slideshow+json">), the same
definitive marker the CLI's `present` command already requires (it
refuses to run without one). Presence-only, not full manifest
validation, so a malformed island still surfaces the tab rather than
disappearing entirely. Also bounce rightPanelTab off "slideshow" to
"renders" if the active composition stops being a slideshow while that
tab is open (e.g. switching files), since its button would otherwise
vanish with no way back to it.

Extracted the gating + scene-list derivation into useSlideshowTabState
to keep StudioRightPanel.tsx under the 600-LOC gate.

packages/studio/src/components/StudioRightPanel.tsx

@@ -1,17 +1,15 @@
-import { useCallback, useEffect, useMemo, useRef, type MutableRefObject } from "react";
+import { useCallback, useEffect, useRef, type MutableRefObject } from "react";
 import { PropertyPanel } from "./editor/PropertyPanel";
 import { LayersPanel } from "./editor/LayersPanel";
 import { CaptionPropertyPanel } from "../captions/components/CaptionPropertyPanel";
 import { BlockParamsPanel } from "./editor/BlockParamsPanel";
 import { RenderQueue } from "./renders/RenderQueue";
 import { SlideshowPanel } from "./panels/SlideshowPanel";
-import type { SceneInfo } from "./panels/SlideshowPanel";
 import { VariablesPanel } from "./panels/VariablesPanel";
 import { PanelTabButton } from "./PanelTabButton";
 import { usePreviewVariablesStore } from "../hooks/previewVariablesStore";
 import type { RenderJob } from "./renders/useRenderQueue";
 import type { BlockParam } from "@hyperframes/core/registry";
-import type { IframeWindow } from "../player/lib/playbackTypes";
 import {
   STUDIO_FLAT_INSPECTOR_ENABLED,
   STUDIO_INSPECTOR_PANELS_ENABLED,
@@ -19,6 +17,7 @@ import {
 import type { Composition } from "@hyperframes/sdk";
 import type { EditHistoryKind } from "../utils/editHistory";
 import { useSlideshowPersist, type UseSlideshowPersistParams } from "../hooks/useSlideshowPersist";
+import { useSlideshowTabState } from "../hooks/useSlideshowTabState";
 import { DesignPanelPromoteProvider } from "./DesignPanelPromoteProvider";
 
 import { useStudioPlaybackContext, useStudioShellContext } from "../contexts/StudioContext";
@@ -168,6 +167,7 @@ export function StudioRightPanel({
     readProjectFile,
     writeProjectFile,
     fileTree,
+    editingFile,
   } = useFileManagerContext();
 
   // Discrete ops (toggle, reorder, add/delete, hotspot): persist immediately,
@@ -216,22 +216,13 @@ export function StudioRightPanel({
   const renderJobs = renderQueue.jobs as RenderJob[];
   const inspectorTabActive = rightPanelTab === "design" || rightPanelTab === "layers";
 
-  // Derive scene list from the live clip manifest in the preview iframe.
-  // fallow-ignore-next-line complexity
-  const slideshowScenes = useMemo<SceneInfo[]>(() => {
-    try {
-      const win = previewIframeRef.current?.contentWindow as IframeWindow | null;
-      return (win?.__clipManifest?.scenes ?? []).map((s) => ({
-        id: s.id,
-        label: s.label,
-        start: s.start,
-        duration: s.duration,
-      }));
-    } catch {
-      return [];
-    }
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [previewIframeRef, rightPanelTab, refreshKey]);
+  const { isSlideshowComposition, slideshowScenes } = useSlideshowTabState({
+    editingFileContent: editingFile?.content,
+    previewIframeRef,
+    refreshKey,
+    rightPanelTab,
+    setRightPanelTab,
+  });
   const designPaneOpen = inspectorTabActive && rightInspectorPanes.design && designPanelActive;
   const layersPaneOpen =
     inspectorTabActive && rightInspectorPanes.layers && STUDIO_INSPECTOR_PANELS_ENABLED;
@@ -506,12 +497,14 @@ export function StudioRightPanel({
                 active={rightPanelTab === "renders"}
                 onClick={() => setRightPanelTab("renders")}
               />
-              <PanelTabButton
-                label="Slideshow"
-                tooltip="Slideshow branching editor"
-                active={rightPanelTab === "slideshow"}
-                onClick={() => setRightPanelTab("slideshow")}
-              />
+              {isSlideshowComposition && (
+                <PanelTabButton
+                  label="Slideshow"
+                  tooltip="Slideshow branching editor"
+                  active={rightPanelTab === "slideshow"}
+                  onClick={() => setRightPanelTab("slideshow")}
+                />
+              )}
               <PanelTabButton
                 label="Variables"
                 tooltip="Template variables — declare, preview with values"
@@ -528,7 +521,7 @@ export function StudioRightPanel({
                   compositionPath={activeBlockParams.compositionPath}
                   onClose={onCloseBlockParams ?? (() => {})}
                 />
-              ) : rightPanelTab === "slideshow" ? (
+              ) : rightPanelTab === "slideshow" && isSlideshowComposition ? (
                 <SlideshowPanel
                   scenes={slideshowScenes}
                   onPersist={onPersistSlideshow}

packages/studio/src/hooks/useSlideshowTabState.test.ts

@@ -0,0 +1,89 @@
+// @vitest-environment happy-dom
+
+import React, { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, describe, expect, it } from "vitest";
+import { useSlideshowTabState } from "./useSlideshowTabState";
+import type { RightPanelTab } from "../utils/studioHelpers";
+
+(globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+const SLIDESHOW_HTML = `<html><body><script type="application/hyperframes-slideshow+json">{"slides":[]}</script></body></html>`;
+const PLAIN_HTML = `<html><body><div id="title">hi</div></body></html>`;
+
+afterEach(() => {
+  document.body.innerHTML = "";
+});
+
+function renderHook(params: {
+  editingFileContent: string | null | undefined;
+  rightPanelTab: RightPanelTab;
+}) {
+  const host = document.createElement("div");
+  document.body.append(host);
+  const root = createRoot(host);
+  const setRightPanelTabCalls: RightPanelTab[] = [];
+  let current: ReturnType<typeof useSlideshowTabState> | null = null;
+
+  function Harness() {
+    current = useSlideshowTabState({
+      editingFileContent: params.editingFileContent,
+      previewIframeRef: { current: null },
+      refreshKey: 0,
+      rightPanelTab: params.rightPanelTab,
+      setRightPanelTab: (tab) => setRightPanelTabCalls.push(tab),
+    });
+    return null;
+  }
+
+  act(() => {
+    root.render(React.createElement(Harness));
+  });
+
+  return {
+    getState: (): ReturnType<typeof useSlideshowTabState> => {
+      if (!current) throw new Error("useSlideshowTabState did not render");
+      return current;
+    },
+    setRightPanelTabCalls,
+    unmount: () => act(() => root.unmount()),
+  };
+}
+
+describe("useSlideshowTabState", () => {
+  it("detects a slideshow composition via the JSON island", () => {
+    const harness = renderHook({ editingFileContent: SLIDESHOW_HTML, rightPanelTab: "design" });
+    expect(harness.getState().isSlideshowComposition).toBe(true);
+    harness.unmount();
+  });
+
+  it("reports false for a plain (non-slideshow) composition", () => {
+    const harness = renderHook({ editingFileContent: PLAIN_HTML, rightPanelTab: "design" });
+    expect(harness.getState().isSlideshowComposition).toBe(false);
+    harness.unmount();
+  });
+
+  it("reports false when there is no editing file yet", () => {
+    const harness = renderHook({ editingFileContent: undefined, rightPanelTab: "design" });
+    expect(harness.getState().isSlideshowComposition).toBe(false);
+    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"]);
+    harness.unmount();
+  });
+
+  it("does not bounce when the composition is a slideshow", () => {
+    const harness = renderHook({ editingFileContent: SLIDESHOW_HTML, rightPanelTab: "slideshow" });
+    expect(harness.setRightPanelTabCalls).toEqual([]);
+    harness.unmount();
+  });
+
+  it("does not bounce a tab other than 'slideshow'", () => {
+    const harness = renderHook({ editingFileContent: PLAIN_HTML, rightPanelTab: "renders" });
+    expect(harness.setRightPanelTabCalls).toEqual([]);
+    harness.unmount();
+  });
+});

packages/studio/src/hooks/useSlideshowTabState.ts

@@ -0,0 +1,59 @@
+import { useEffect, useMemo, type MutableRefObject } from "react";
+import { 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";
+
+/**
+ * Derives whether the currently-edited composition is a slideshow (carries
+ * the slideshow JSON island — the same definitive marker the CLI's `present`
+ * command requires; it refuses to run without one) and the live scene list
+ * for the Slideshow panel, and bounces `rightPanelTab` off "slideshow" the
+ * moment it stops applying (e.g. the user switches to a non-slideshow file
+ * while that tab was open) so the panel never shows a dangling active tab
+ * whose button is no longer even rendered.
+ *
+ * Extracted from StudioRightPanel to keep that file under the 600-LOC gate.
+ */
+export function useSlideshowTabState(params: {
+  editingFileContent: string | null | undefined;
+  previewIframeRef: MutableRefObject<HTMLIFrameElement | null>;
+  refreshKey: number;
+  rightPanelTab: RightPanelTab;
+  setRightPanelTab: (tab: RightPanelTab) => void;
+}): { isSlideshowComposition: boolean; slideshowScenes: SceneInfo[] } {
+  const { editingFileContent, previewIframeRef, refreshKey, rightPanelTab, setRightPanelTab } =
+    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],
+  );
+
+  // Derive scene list from the live clip manifest in the preview iframe.
+  const slideshowScenes = useMemo<SceneInfo[]>(() => {
+    try {
+      const win = previewIframeRef.current?.contentWindow as IframeWindow | null;
+      return (win?.__clipManifest?.scenes ?? []).map((s) => ({
+        id: s.id,
+        label: s.label,
+        start: s.start,
+        duration: s.duration,
+      }));
+    } catch {
+      return [];
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [previewIframeRef, rightPanelTab, refreshKey]);
+
+  useEffect(() => {
+    if (rightPanelTab === "slideshow" && !isSlideshowComposition) {
+      setRightPanelTab("renders");
+    }
+  }, [rightPanelTab, isSlideshowComposition, setRightPanelTab]);
+
+  return { isSlideshowComposition, slideshowScenes };
+}