diff --git a/packages/cli/src/utils/compositionServer.ts b/packages/cli/src/utils/compositionServer.ts
index 13b6ae4309..24c46a5036 100644
--- a/packages/cli/src/utils/compositionServer.ts
+++ b/packages/cli/src/utils/compositionServer.ts
@@ -3,6 +3,7 @@
 // composition asset files, and binding to a free port.
 import { existsSync } from "node:fs";
 import { resolve, dirname } from "node:path";
+import { fileURLToPath } from "node:url";
 
 /** Minimal surface of a listening server (satisfied by @hono/node-server's ServerType). */
 interface PortBindable {
@@ -15,7 +16,9 @@ interface PortBindable {
 }
 
 function helperDir(): string {
-  return dirname(new URL(import.meta.url).pathname);
+  // fileURLToPath (not URL.pathname) so the Windows "/D:/..." leading-slash form
+  // doesn't break the bundle-path resolution below.
+  return dirname(fileURLToPath(import.meta.url));
 }
 
 export function resolveRuntimePath(): string | null {
diff --git a/packages/core/src/lint/rules/slideshow.ts b/packages/core/src/lint/rules/slideshow.ts
index 2731a47512..80b5d8f449 100644
--- a/packages/core/src/lint/rules/slideshow.ts
+++ b/packages/core/src/lint/rules/slideshow.ts
@@ -1,20 +1,11 @@
-// fallow-ignore-file code-duplication
 import type { LintContext, HyperframeLintFinding } from "../context";
 import type { LintRule } from "../types";
 import { readAttr } from "../utils";
 import { parseSlideshowManifest, resolveSlideshow } from "../../slideshow/parseSlideshow";
+import { isSceneLikeCompositionId } from "../../slideshow/sceneId";
 
 type Scene = { id: string; start: number; duration: number };
 
-/** Mirrors isSceneLikeCompositionId in packages/core/src/runtime/timeline.ts */
-function isSceneLikeCompositionId(compositionId: string): boolean {
-  const normalized = compositionId.trim().toLowerCase();
-  if (!normalized || normalized === "main") return false;
-  if (normalized.includes("caption")) return false;
-  if (normalized.includes("ambient")) return false;
-  return true;
-}
-
 function parseTiming(raw: string): { start: number; duration: number } | null {
   const startStr = readAttr(raw, "data-start");
   if (startStr === null) return null;
diff --git a/packages/core/src/runtime/timeline.ts b/packages/core/src/runtime/timeline.ts
index e6328d73a8..6f8e583818 100644
--- a/packages/core/src/runtime/timeline.ts
+++ b/packages/core/src/runtime/timeline.ts
@@ -7,6 +7,7 @@ import type {
 import { swallow } from "./diagnostics";
 import { readElementPlaybackRate } from "./media";
 import { createRuntimeStartTimeResolver } from "./startResolver";
+import { isSceneLikeCompositionId } from "../slideshow/sceneId";
 
 const AUTHORED_DURATION_ATTR = "data-hf-authored-duration";
 const AUTHORED_END_ATTR = "data-hf-authored-end";
@@ -230,13 +231,6 @@ export function collectRuntimeTimelinePayload(params: {
     }
     return maxWindowEndSeconds > 0 ? maxWindowEndSeconds : null;
   };
-  const isSceneLikeCompositionId = (compositionId: string): boolean => {
-    const normalized = compositionId.trim().toLowerCase();
-    if (!normalized || normalized === "main") return false;
-    if (normalized.includes("caption")) return false;
-    if (normalized.includes("ambient")) return false;
-    return true;
-  };
   const resolveNearestCompositionContext = (
     node: Element,
     root: Element | null,
diff --git a/packages/core/src/slideshow/parseSlideshow.test.ts b/packages/core/src/slideshow/parseSlideshow.test.ts
index d9207243fb..1633d58818 100644
--- a/packages/core/src/slideshow/parseSlideshow.test.ts
+++ b/packages/core/src/slideshow/parseSlideshow.test.ts
@@ -37,6 +37,11 @@ describe("parseSlideshowManifest", () => {
     expect(() => parseSlideshowManifest(html)).toThrow();
   });
 
+  it("rejects a non-object manifest (e.g. a JSON array)", () => {
+    const html = `<script type="application/hyperframes-slideshow+json">[42, null]</script>`;
+    expect(() => parseSlideshowManifest(html)).toThrow();
+  });
+
   it("throws when a slide entry is malformed (sceneId not a string)", () => {
     const html = `<script type="application/hyperframes-slideshow+json">
       { "slides": [{ "sceneId": 42 }] }
@@ -74,6 +79,18 @@ describe("resolveSlideshow", () => {
     expect(errors.some((e) => e.includes("missing"))).toBe(true);
   });
 
+  it("flags duplicate slideSequence ids instead of silently overwriting", () => {
+    const m: import("./slideshow.types").SlideshowManifest = {
+      slides: [{ sceneId: "a" }],
+      slideSequences: [
+        { id: "dup", label: "First", slides: [{ sceneId: "c" }] },
+        { id: "dup", label: "Second", slides: [{ sceneId: "c" }] },
+      ],
+    };
+    const { errors } = resolveSlideshow(m, SCENES);
+    expect(errors.some((e) => e.includes("duplicate slideSequence id"))).toBe(true);
+  });
+
   it("reports an error for a fragment outside the slide range", () => {
     const m: import("./slideshow.types").SlideshowManifest = {
       slides: [{ sceneId: "a", fragments: [99] }],
diff --git a/packages/core/src/slideshow/parseSlideshow.ts b/packages/core/src/slideshow/parseSlideshow.ts
index ba96fc9fb0..a7583f8406 100644
--- a/packages/core/src/slideshow/parseSlideshow.ts
+++ b/packages/core/src/slideshow/parseSlideshow.ts
@@ -69,7 +69,7 @@ function isSlideSequence(v: unknown): boolean {
 }
 
 function isManifest(v: unknown): v is SlideshowManifest {
-  if (typeof v !== "object" || v === null) return false;
+  if (typeof v !== "object" || v === null || Array.isArray(v)) return false;
   const o = v as Record<string, unknown>;
   if (!Array.isArray(o["slides"]) || !o["slides"].every(isSlideRef)) return false;
   if (o["slideSequences"] !== undefined) {
@@ -158,6 +158,10 @@ export function resolveSlideshow(
 
   const sequences: Record<string, ResolvedSlideSequence> = {};
   for (const seq of manifest.slideSequences ?? []) {
+    // Flag duplicate sequence ids rather than silently overwriting the earlier one.
+    if (Object.prototype.hasOwnProperty.call(sequences, seq.id)) {
+      errors.push(`duplicate slideSequence id "${seq.id}" — only the last definition is kept`);
+    }
     sequences[seq.id] = {
       id: seq.id,
       label: seq.label,
diff --git a/packages/core/src/slideshow/sceneId.ts b/packages/core/src/slideshow/sceneId.ts
new file mode 100644
index 0000000000..605a3cf478
--- /dev/null
+++ b/packages/core/src/slideshow/sceneId.ts
@@ -0,0 +1,15 @@
+// packages/core/src/slideshow/sceneId.ts
+
+/**
+ * Whether a composition id names a "scene-like" composition — i.e. a real slide
+ * scene, not the root timeline (`main`) or a non-scene overlay (captions, ambient
+ * layers). Shared by the runtime scene-window computation and the slideshow lint
+ * rule so the two can never drift.
+ */
+export function isSceneLikeCompositionId(compositionId: string): boolean {
+  const normalized = compositionId.trim().toLowerCase();
+  if (!normalized || normalized === "main") return false;
+  if (normalized.includes("caption")) return false;
+  if (normalized.includes("ambient")) return false;
+  return true;
+}
diff --git a/packages/player/src/slideshow/hyperframes-slideshow.test.ts b/packages/player/src/slideshow/hyperframes-slideshow.test.ts
index 2596235998..f76372153c 100644
--- a/packages/player/src/slideshow/hyperframes-slideshow.test.ts
+++ b/packages/player/src/slideshow/hyperframes-slideshow.test.ts
@@ -2,6 +2,7 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 import { handleRuntimeMessage } from "../runtime-message-handler.js";
 import { dropInvalidSlides } from "./hyperframes-slideshow.js";
+import { slideshowChannelName } from "./slideshowPresenter.js";
 
 // Dynamic import defers custom-element registration until happy-dom is active.
 // (Static top-level imports execute before the test environment is set up, which
@@ -524,7 +525,7 @@ describe("<hyperframes-slideshow> presenter mode", () => {
   const tick = () => new Promise<void>((r) => setTimeout(r, 0));
 
   it("audience mode: mirrors full position (sequence + slide + fragment) via syncTo", async () => {
-    const presenterChannel = new BroadcastChannel("hf-slideshow");
+    const presenterChannel = new BroadcastChannel(slideshowChannelName());
     const { el, getLastSync } = makeAudienceEl();
 
     await tick();
@@ -542,7 +543,7 @@ describe("<hyperframes-slideshow> presenter mode", () => {
   });
 
   it("audience mode: mirrors a branch position too (full sequenceId forwarded to syncTo)", async () => {
-    const presenterChannel = new BroadcastChannel("hf-slideshow");
+    const presenterChannel = new BroadcastChannel(slideshowChannelName());
     const { el, getLastSync } = makeAudienceEl();
 
     await tick();
@@ -566,7 +567,7 @@ describe("<hyperframes-slideshow> presenter mode", () => {
 
   it("presenter mode: posts position to channel on controller onChange", async () => {
     const received: unknown[] = [];
-    const listenerChannel = new BroadcastChannel("hf-slideshow");
+    const listenerChannel = new BroadcastChannel(slideshowChannelName());
     listenerChannel.onmessage = (e: MessageEvent) => received.push(e.data);
 
     const { el, triggerChange } = makePresenterEl();
@@ -608,7 +609,7 @@ describe("<hyperframes-slideshow> presenter mode", () => {
     await tick();
 
     const received: unknown[] = [];
-    const spy = new BroadcastChannel("hf-slideshow");
+    const spy = new BroadcastChannel(slideshowChannelName());
     spy.onmessage = (e: MessageEvent) => received.push(e.data);
 
     el.remove(); // triggers disconnectedCallback
diff --git a/packages/player/src/slideshow/hyperframes-slideshow.ts b/packages/player/src/slideshow/hyperframes-slideshow.ts
index 317bd15bd0..840881141e 100644
--- a/packages/player/src/slideshow/hyperframes-slideshow.ts
+++ b/packages/player/src/slideshow/hyperframes-slideshow.ts
@@ -114,6 +114,17 @@ export class HyperframesSlideshow extends HTMLElement {
     }
   }
 
+  // Observe the attributes the component reads so runtime toggles take effect.
+  static get observedAttributes(): string[] {
+    return ["sound", "mode"];
+  }
+
+  attributeChangedCallback(): void {
+    // Re-render once bound so a flipped `sound`/`mode` is reflected (mute button,
+    // audience-vs-presenter chrome). No-op before the controller binds.
+    if (this.controller) this.render();
+  }
+
   connectedCallback(): void {
     this.disconnected = false;
     this.initInFlight = false;
@@ -178,7 +189,9 @@ export class HyperframesSlideshow extends HTMLElement {
    */
   present(): void {
     const sep = location.search ? "&" : "?";
-    window.open(location.href + sep + "mode=audience", "_blank");
+    // noopener,noreferrer: the audience window must not get a reference back to
+    // this window (it syncs over BroadcastChannel, not window.opener).
+    window.open(location.href + sep + "mode=audience", "_blank", "noopener,noreferrer");
     this.setAttribute("data-hf-presenting", "true");
     this.presenterStartMs = Date.now();
     if (this.presenterInterval === null) {
@@ -278,6 +291,19 @@ export class HyperframesSlideshow extends HTMLElement {
       };
 
       this.bindController(new SlideshowController(port, cleaned));
+
+      // Slow-iframe recovery: if the scene timeline hadn't posted yet (empty
+      // scenes → sceneId-based slides were dropped), re-init once when it finally
+      // arrives so those slides resolve instead of being permanently lost.
+      if (scenes.length === 0 && manifest.slides.length > 0) {
+        playerEl.addEventListener(
+          "scenes",
+          () => {
+            if (gen === this.initGeneration) void this.init();
+          },
+          { once: true },
+        );
+      }
     } finally {
       this.initInFlight = false;
     }
@@ -318,7 +344,10 @@ export class HyperframesSlideshow extends HTMLElement {
     // Arrows act even when nothing is focused (active === body/null) so a freshly
     // loaded deck responds without a click; Space/Backspace have strong page-level
     // defaults (scroll / history) so they only act when the deck actually has focus.
-    const ambient = focused || active === document.body || active === null;
+    // When several decks share a page, drop the unfocused-convenience so a key
+    // doesn't drive every instance at once — only the focused deck responds.
+    const multiInstance = document.querySelectorAll("hyperframes-slideshow").length > 1;
+    const ambient = focused || (!multiInstance && (active === document.body || active === null));
     if (e.key === "ArrowRight") {
       if (!ambient) return;
       this.controller.next();
diff --git a/packages/player/src/slideshow/slideshowPresenter.ts b/packages/player/src/slideshow/slideshowPresenter.ts
index 5bee6fd3ec..6345ba0a64 100644
--- a/packages/player/src/slideshow/slideshowPresenter.ts
+++ b/packages/player/src/slideshow/slideshowPresenter.ts
@@ -27,6 +27,16 @@ function isGotoMessage(data: unknown): data is GotoMessage {
  * Presenter (default) mode: posts position updates to the channel.
  * Audience mode: listens for goto messages and calls the provided handler.
  */
+/**
+ * Per-deck channel name. The presenter and its audience window load the same URL
+ * (path), so keying on pathname keeps them paired while isolating other decks
+ * presenting on the same origin (which would otherwise cross-talk on a fixed name).
+ */
+export function slideshowChannelName(): string {
+  const path = typeof location !== "undefined" ? location.pathname : "";
+  return `hf-slideshow:${path}`;
+}
+
 export class SlideshowChannel {
   private channel: BroadcastChannel | null = null;
 
@@ -35,7 +45,7 @@ export class SlideshowChannel {
     private readonly onGoto: (msg: GotoMessage) => void,
   ) {
     try {
-      this.channel = new BroadcastChannel("hf-slideshow");
+      this.channel = new BroadcastChannel(slideshowChannelName());
     } catch {
       // BroadcastChannel unavailable (e.g. unsupported env); degrade silently.
       return;
diff --git a/packages/player/vitest.config.ts b/packages/player/vitest.config.ts
index 64effe32c5..5f8f7a426a 100644
--- a/packages/player/vitest.config.ts
+++ b/packages/player/vitest.config.ts
@@ -1,7 +1,10 @@
 import { defineConfig } from "vitest/config";
-import { resolve } from "path";
+import { resolve } from "node:path";
+import { fileURLToPath } from "node:url";
 
-const coreRoot = resolve(new URL("..", import.meta.url).pathname, "core/src");
+// fileURLToPath (not URL.pathname): on Windows .pathname yields "/D:/..." with a
+// leading slash, which breaks resolve() and the alias below.
+const coreRoot = resolve(fileURLToPath(new URL("../core/src", import.meta.url)));
 
 export default defineConfig({
   resolve: {
diff --git a/packages/producer/src/utils/paths.ts b/packages/producer/src/utils/paths.ts
index ebf8688ca0..7ff314517f 100644
--- a/packages/producer/src/utils/paths.ts
+++ b/packages/producer/src/utils/paths.ts
@@ -9,6 +9,7 @@ import {
   relative as nodeRelative,
   isAbsolute as nodeIsAbsolute,
 } from "node:path";
+import { fileURLToPath } from "node:url";
 
 export interface RenderPaths {
   absoluteProjectDir: string;
@@ -17,7 +18,9 @@ export interface RenderPaths {
 
 const DEFAULT_RENDERS_DIR =
   process.env.PRODUCER_RENDERS_DIR ??
-  nodeResolve(new URL(import.meta.url).pathname, "../../..", "renders");
+  // fileURLToPath (not URL.pathname): on Windows .pathname is "/D:/..." which
+  // resolves to a bogus renders dir.
+  nodeResolve(fileURLToPath(import.meta.url), "../../..", "renders");
 
 type PathModuleLike = {
   resolve: (...segments: string[]) => string;
diff --git a/packages/studio/src/components/panels/SlideshowPanel.test.ts b/packages/studio/src/components/panels/SlideshowPanel.test.ts
index 6ea185c09c..42ca46fdea 100644
--- a/packages/studio/src/components/panels/SlideshowPanel.test.ts
+++ b/packages/studio/src/components/panels/SlideshowPanel.test.ts
@@ -2,6 +2,7 @@ import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import {
   toggleMainLineSlide,
   reorderMainLineSlide,
+  reorderBranchSlide,
   setSlideNotes,
   addFragment,
   removeFragment,
@@ -67,6 +68,29 @@ describe("reorderMainLineSlide", () => {
   });
 });
 
+// ── reorderBranchSlide ─────────────────────────────────────────────────────
+describe("reorderBranchSlide", () => {
+  const base: SlideshowManifest = {
+    slides: [{ sceneId: "x" }],
+    slideSequences: [
+      { id: "b1", label: "Branch", slides: [{ sceneId: "a" }, { sceneId: "b" }, { sceneId: "c" }] },
+    ],
+  };
+
+  it("moves a branch slide down within its sequence (main line untouched)", () => {
+    const m = reorderBranchSlide(base, "b1", "a", "down");
+    expect(m.slideSequences?.[0].slides.map((s) => s.sceneId)).toEqual(["b", "a", "c"]);
+    expect(m.slides).toEqual(base.slides);
+  });
+
+  it("is a no-op at the boundary and for an unknown branch/scene", () => {
+    expect(reorderBranchSlide(base, "b1", "a", "up").slideSequences?.[0].slides[0].sceneId).toBe(
+      "a",
+    );
+    expect(reorderBranchSlide(base, "nope", "a", "down")).toEqual(base);
+  });
+});
+
 // ── setSlideNotes ──────────────────────────────────────────────────────────
 
 describe("setSlideNotes", () => {
diff --git a/packages/studio/src/components/panels/SlideshowPanel.tsx b/packages/studio/src/components/panels/SlideshowPanel.tsx
index b04da2d40f..9d58cea9a5 100644
--- a/packages/studio/src/components/panels/SlideshowPanel.tsx
+++ b/packages/studio/src/components/panels/SlideshowPanel.tsx
@@ -32,6 +32,7 @@ import {
 export {
   toggleMainLineSlide,
   reorderMainLineSlide,
+  reorderBranchSlide,
   setSlideNotes,
   addFragment,
   removeFragment,
@@ -56,6 +57,7 @@ export function safeParseManifest(html: string): SlideshowManifest {
 import {
   toggleMainLineSlide,
   reorderMainLineSlide,
+  reorderBranchSlide,
   setSlideNotes,
   addFragment,
   removeFragment,
@@ -101,7 +103,9 @@ export function makeSlideshowNotesController(): NotesController {
         const p = pending;
         if (p !== null) {
           pending = null;
-          p.persist(p.manifest).catch(() => {});
+          p.persist(p.manifest).catch((err: unknown) => {
+            console.error("[slideshow] notes persist failed:", err);
+          });
         }
       }, delayMs);
       return timer;
@@ -115,7 +119,9 @@ export function makeSlideshowNotesController(): NotesController {
       const p = pending;
       if (p !== null) {
         pending = null;
-        p.persist(p.manifest).catch(() => {});
+        p.persist(p.manifest).catch((err: unknown) => {
+          console.error("[slideshow] notes persist failed:", err);
+        });
       }
     },
 
@@ -215,7 +221,12 @@ export function SlideshowPanel({ scenes, onPersist, onPersistNotes }: SlideshowP
       const merged = notesCtrlRef.current.mergeIntoDiscrete(next);
       setManifest(merged);
       manifestRef.current = merged;
-      await onPersist(merged);
+      // Surface persist failures instead of swallowing them at each call site.
+      try {
+        await onPersist(merged);
+      } catch (err) {
+        console.error("[slideshow] failed to persist manifest edit:", err);
+      }
     },
     [onPersist],
   );
@@ -282,6 +293,15 @@ export function SlideshowPanel({ scenes, onPersist, onPersistNotes }: SlideshowP
     [applyManifest],
   );
 
+  const handleReorderBranchSlide = useCallback(
+    (sequenceId: string, sceneId: string, dir: "up" | "down") => {
+      applyManifest(reorderBranchSlide(manifestRef.current, sequenceId, sceneId, dir)).catch(
+        () => {},
+      );
+    },
+    [applyManifest],
+  );
+
   const handleSetNotes = useCallback(
     (notes: string) => {
       if (!selectedSceneId) return;
@@ -331,6 +351,16 @@ export function SlideshowPanel({ scenes, onPersist, onPersistNotes }: SlideshowP
 
   const handleDeleteSequence = useCallback(
     (id: string) => {
+      // Deleting a branch removes its slides and orphans any hotspot targeting it —
+      // confirm first to prevent accidental data loss.
+      const seq = (manifestRef.current.slideSequences ?? []).find((s) => s.id === id);
+      const count = seq?.slides.length ?? 0;
+      const label = seq?.label ?? id;
+      const ok = window.confirm(
+        `Delete branch "${label}"${count ? ` and its ${count} slide${count === 1 ? "" : "s"}` : ""}? ` +
+          `Hotspots pointing to it will no longer resolve.`,
+      );
+      if (!ok) return;
       applyManifest(deleteSequence(manifestRef.current, id)).catch(() => {});
     },
     [applyManifest],
@@ -429,6 +459,7 @@ export function SlideshowPanel({ scenes, onPersist, onPersistNotes }: SlideshowP
           selectedSceneId={selectedSceneId}
           selectedSequenceId={selectedSequenceId}
           onSelectBranchSlide={handleSelectBranchSlide}
+          onReorderBranchSlide={handleReorderBranchSlide}
         />
       )}
 
diff --git a/packages/studio/src/components/panels/SlideshowSubPanels.tsx b/packages/studio/src/components/panels/SlideshowSubPanels.tsx
index 39aaa11fdc..a03c29262b 100644
--- a/packages/studio/src/components/panels/SlideshowSubPanels.tsx
+++ b/packages/studio/src/components/panels/SlideshowSubPanels.tsx
@@ -216,6 +216,7 @@ export interface BranchTreeProps {
   selectedSceneId: string | null;
   selectedSequenceId: string | null;
   onSelectBranchSlide: (sequenceId: string, sceneId: string) => void;
+  onReorderBranchSlide: (sequenceId: string, sceneId: string, dir: "up" | "down") => void;
 }
 
 export function BranchTree({
@@ -228,6 +229,7 @@ export function BranchTree({
   selectedSceneId,
   selectedSequenceId,
   onSelectBranchSlide,
+  onReorderBranchSlide,
 }: BranchTreeProps) {
   const [newLabel, setNewLabel] = useState("");
   const inputId = useId();
@@ -278,6 +280,7 @@ export function BranchTree({
               selectedSceneId={selectedSceneId}
               selectedSequenceId={selectedSequenceId}
               onSelectBranchSlide={onSelectBranchSlide}
+              onReorderBranchSlide={onReorderBranchSlide}
             />
           ))}
         </div>
@@ -295,6 +298,7 @@ interface BranchItemProps {
   selectedSceneId: string | null;
   selectedSequenceId: string | null;
   onSelectBranchSlide: (sequenceId: string, sceneId: string) => void;
+  onReorderBranchSlide: (sequenceId: string, sceneId: string, dir: "up" | "down") => void;
 }
 
 function BranchItem({
@@ -306,6 +310,7 @@ function BranchItem({
   selectedSceneId,
   selectedSequenceId,
   onSelectBranchSlide,
+  onReorderBranchSlide,
 }: BranchItemProps) {
   const [editing, setEditing] = useState(false);
   const [draft, setDraft] = useState(seq.label);
@@ -357,7 +362,8 @@ function BranchItem({
       </div>
       <div className="flex flex-col gap-px pl-2">
         {scenes.map((scene) => {
-          const assigned = seq.slides.some((s) => s.sceneId === scene.id);
+          const branchPos = seq.slides.findIndex((s) => s.sceneId === scene.id);
+          const assigned = branchPos !== -1;
           const isSelected = selectedSequenceId === seq.id && selectedSceneId === scene.id;
           return (
             <div
@@ -372,16 +378,39 @@ function BranchItem({
                 className="accent-studio-accent flex-shrink-0"
               />
               {assigned ? (
-                <button
-                  type="button"
-                  aria-pressed={isSelected}
-                  className={`flex-1 text-left truncate transition-colors hover:text-neutral-200 ${
-                    isSelected ? "text-white" : "text-neutral-400"
-                  }`}
-                  onClick={() => onSelectBranchSlide(seq.id, scene.id)}
-                >
-                  {scene.label || scene.id}
-                </button>
+                <>
+                  <button
+                    type="button"
+                    aria-pressed={isSelected}
+                    className={`flex-1 text-left truncate transition-colors hover:text-neutral-200 ${
+                      isSelected ? "text-white" : "text-neutral-400"
+                    }`}
+                    onClick={() => onSelectBranchSlide(seq.id, scene.id)}
+                  >
+                    {scene.label || scene.id}
+                  </button>
+                  <span className="text-[9px] text-neutral-600 tabular-nums flex-shrink-0">
+                    {branchPos + 1}/{seq.slides.length}
+                  </span>
+                  <button
+                    type="button"
+                    aria-label={`Move ${scene.label || scene.id} earlier in branch ${seq.label}`}
+                    disabled={branchPos <= 0}
+                    className="text-[10px] text-neutral-500 hover:text-neutral-200 disabled:opacity-30 disabled:cursor-default px-0.5"
+                    onClick={() => onReorderBranchSlide(seq.id, scene.id, "up")}
+                  >
+                    ▲
+                  </button>
+                  <button
+                    type="button"
+                    aria-label={`Move ${scene.label || scene.id} later in branch ${seq.label}`}
+                    disabled={branchPos >= seq.slides.length - 1}
+                    className="text-[10px] text-neutral-500 hover:text-neutral-200 disabled:opacity-30 disabled:cursor-default px-0.5"
+                    onClick={() => onReorderBranchSlide(seq.id, scene.id, "down")}
+                  >
+                    ▼
+                  </button>
+                </>
               ) : (
                 <span className="flex-1 truncate">{scene.label || scene.id}</span>
               )}
diff --git a/packages/studio/src/components/panels/slideshowPanelHelpers.ts b/packages/studio/src/components/panels/slideshowPanelHelpers.ts
index 77b574fa21..9c64eb64df 100644
--- a/packages/studio/src/components/panels/slideshowPanelHelpers.ts
+++ b/packages/studio/src/components/panels/slideshowPanelHelpers.ts
@@ -30,22 +30,37 @@ export function toggleMainLineSlide(
 
 // fallow-ignore-next-line complexity
 /** Move a main-line slide up or down by one position. */
+/** Swap the slide with `sceneId` one step up/down within a slide list. */
+function swapSlide(slides: SlideRef[], sceneId: string, direction: "up" | "down"): SlideRef[] {
+  const idx = slides.findIndex((s) => s.sceneId === sceneId);
+  if (idx === -1) return slides;
+  const next = direction === "up" ? idx - 1 : idx + 1;
+  if (next < 0 || next >= slides.length) return slides;
+  const out = [...slides];
+  const a = out[idx];
+  const b = out[next];
+  if (!a || !b) return slides;
+  out[idx] = b;
+  out[next] = a;
+  return out;
+}
+
 export function reorderMainLineSlide(
   manifest: SlideshowManifest,
   sceneId: string,
   direction: "up" | "down",
 ): SlideshowManifest {
-  const idx = manifest.slides.findIndex((s) => s.sceneId === sceneId);
-  if (idx === -1) return manifest;
-  const next = direction === "up" ? idx - 1 : idx + 1;
-  if (next < 0 || next >= manifest.slides.length) return manifest;
-  const slides = [...manifest.slides];
-  const a = slides[idx];
-  const b = slides[next];
-  if (!a || !b) return manifest;
-  slides[idx] = b;
-  slides[next] = a;
-  return { ...manifest, slides };
+  return mapSlidesIn(manifest, undefined, (slides) => swapSlide(slides, sceneId, direction));
+}
+
+/** Reorder a slide within a branch sequence (parallel to reorderMainLineSlide). */
+export function reorderBranchSlide(
+  manifest: SlideshowManifest,
+  sequenceId: string,
+  sceneId: string,
+  direction: "up" | "down",
+): SlideshowManifest {
+  return mapSlidesIn(manifest, sequenceId, (slides) => swapSlide(slides, sceneId, direction));
 }
 
 /** Apply fn to a branch's slide list (sequenceId) or the main line (undefined). */
diff --git a/packages/studio/src/utils/setSlideshowManifest.ts b/packages/studio/src/utils/setSlideshowManifest.ts
index 78fd11c17c..7a00593411 100644
--- a/packages/studio/src/utils/setSlideshowManifest.ts
+++ b/packages/studio/src/utils/setSlideshowManifest.ts
@@ -20,6 +20,7 @@ import type { SlideshowManifest } from "@hyperframes/core/slideshow";
 import {
   SLIDESHOW_ISLAND_TYPE,
   SLIDESHOW_MANIFEST_VERSION,
+  parseSlideshowManifest,
   slideshowIslandRegex,
 } from "@hyperframes/core/slideshow";
 import type { Composition } from "@hyperframes/sdk";
@@ -64,6 +65,18 @@ export async function persistSlideshowManifest(args: PersistSlideshowArgs): Prom
   const { manifest, sdkSession, originalContent, targetPath, deps, label, coalesceKey } = args;
 
   const islandHtml = buildSlideshowIslandHtml(manifest);
+
+  // Write-time validation: confirm the island we just built round-trips to a
+  // valid manifest before touching disk, so a malformed edit can't corrupt the
+  // composition. parseSlideshowManifest throws on a structurally-invalid island.
+  try {
+    if (!parseSlideshowManifest(islandHtml)) {
+      throw new Error("built island did not parse back to a manifest");
+    }
+  } catch (err) {
+    throw new Error(`refusing to persist invalid slideshow manifest: ${(err as Error).message}`);
+  }
+
   const current = sdkSession.serialize();
 
   // Strip ALL existing islands (handles the case where two stale islands
@@ -78,6 +91,10 @@ export async function persistSlideshowManifest(args: PersistSlideshowArgs): Prom
     after = stripped + "\n" + islandHtml;
   }
 
+  // No-op gate: if the rewritten HTML is byte-identical to the current serialized
+  // HTML, skip the write — avoids a spurious disk write and a no-op undo entry.
+  if (after === current) return;
+
   await persistSdkSerialize(after, targetPath, originalContent, deps, {
     label: label ?? "Edit slideshow",
     ...(coalesceKey ? { coalesceKey } : {}),