fix(studio): give the motion path and the fallbacks a one-element target

The narrowing this branch adds missed the motion-path overlay, and every
caller that could not narrow fell back to the exact bare class the narrowing
exists to replace.

- motionPathSelection.selectorFor now goes through writeTargetSelector. It
  feeds both the geometry read and the "set destination" write, so a class
  sibling measured its home off the FIRST sibling and then authored
  add-motion-path onto all of them. The toolbar toggle hides when no
  one-element form exists rather than arming a press that is dropped.
- The five new-tween writers that fell back to the selection's own selector
  now drop the commit instead. A gesture that does not persist reverts on the
  next reload; a tween silently aimed at five elements does not.
- tweenTargetsElement only follows the DOM to a target that matches exactly
  one element. A target the element merely shares with its siblings is a group
  tween, and these callers mutate what they find, so an individual nudge was
  rewriting the group's own tween and moving all five.

packages/studio/src/components/editor/MotionPathOverlay.tsx

@@ -132,7 +132,10 @@ export const MotionPathOverlay = memo(function MotionPathOverlay({
   const createMode = geometryResolved && !geometry && Boolean(selection?.element) && !isPlaying;
   const createSelector = createMode ? selectorFor(selection) : null;
   const compW = compositionSize?.width ?? null;
-  const canCreate = createMode && hasMotionPathPlugin(iframeRef.current);
+  // No one-element selector means the path could only be authored onto the
+  // element's class siblings, so the toolbar toggle stays hidden instead of
+  // arming a press that the effect below would silently drop.
+  const canCreate = createMode && !!createSelector && hasMotionPathPlugin(iframeRef.current);
 
   // Publish whether the selected element can take a path so the preview toolbar
   // shows its "set destination" toggle. Drops to false when this overlay unmounts

packages/studio/src/components/editor/motionPathSelection.test.ts

@@ -0,0 +1,65 @@
+// @vitest-environment jsdom
+import { afterEach, describe, expect, it } from "vitest";
+import type { DomEditSelection } from "./domEditingTypes";
+import { buildStableSelector, getSelectorIndex } from "./domEditingDom";
+import { selectorFor } from "./motionPathSelection";
+
+afterEach(() => {
+  document.body.innerHTML = "";
+});
+
+function selectionFor(el: HTMLElement): DomEditSelection {
+  const selector = buildStableSelector(el);
+  return {
+    element: el,
+    id: el.id || undefined,
+    hfId: el.getAttribute("data-hf-id") || undefined,
+    selector,
+    selectorIndex: getSelectorIndex(document, el, selector, "index.html", null),
+    sourceFile: "index.html",
+    dataAttributes: { start: "0", duration: "2" },
+  } as unknown as DomEditSelection;
+}
+
+function mountGroupSiblings(): HTMLElement[] {
+  document.body.innerHTML = `
+    <div id="scene" class="clip" data-start="0" data-duration="2">
+      <div class="group"></div>
+      <div class="group"></div>
+      <div class="group"></div>
+    </div>
+  `;
+  return Array.from(document.querySelectorAll<HTMLElement>(".group"));
+}
+
+describe("selectorFor", () => {
+  it("addresses one element for a class-only sibling", () => {
+    const groups = mountGroupSiblings();
+    const selector = selectorFor(selectionFor(groups[2]!));
+
+    // The bare ".group" both measured home off the FIRST sibling and wrote the
+    // new motion path onto all three.
+    expect(selector).not.toBe(".group");
+    expect(document.querySelectorAll(selector!)).toHaveLength(1);
+    expect(document.querySelector(selector!)).toBe(groups[2]);
+  });
+
+  it("keeps a unique id target", () => {
+    document.body.innerHTML = `<div id="hero"></div>`;
+    const el = document.querySelector<HTMLElement>("#hero")!;
+
+    expect(selectorFor(selectionFor(el))).toBe("#hero");
+  });
+
+  it("returns null with no selection", () => {
+    expect(selectorFor(null)).toBeNull();
+  });
+
+  it("returns null when no rung addresses one element", () => {
+    const groups = mountGroupSiblings();
+    const selection = selectionFor(groups[1]!);
+    groups[1]!.remove();
+
+    expect(selectorFor(selection)).toBeNull();
+  });
+});

packages/studio/src/components/editor/motionPathSelection.ts

@@ -5,11 +5,21 @@
  */
 import type { GsapAnimation } from "@hyperframes/parsers/gsap-parser";
 import type { DomEditSelection } from "./domEditing";
+import { writeTargetSelector } from "../../hooks/gsapShared";
 
+/**
+ * The selector the overlay both MEASURES the element by and authors a new
+ * motion path against.
+ *
+ * Both halves need exactly one element. The selection's own selector is a bare
+ * class for an id-less element, so a `.group` sibling read its home position off
+ * the FIRST sibling (skewing the destination the click computes) and then wrote
+ * `add-motion-path` onto all five. `writeTargetSelector` is the same one-element
+ * narrowing every other new-tween writer goes through; null means no such form
+ * exists, and the overlay hides "set destination" rather than write a wrong one.
+ */
 export function selectorFor(sel: DomEditSelection | null): string | null {
-  if (!sel) return null;
-  if (sel.id) return `#${CSS.escape(sel.id)}`;
-  return sel.selector ?? null;
+  return sel ? writeTargetSelector(sel) : null;
 }
 
 /** The animation whose path is editable on-canvas: literal, statically resolved,

packages/studio/src/hooks/gsapDragCommit.ts

@@ -51,9 +51,14 @@ export interface GsapDragCommitCallbacks {
  * write over every sibling sharing the class. Retargets of an EXISTING tween
  * must NOT come through here (they keep `anim.targetSelector`, so a tween the
  * author aimed at a group stays aimed at it).
+ *
+ * Null means no one-element form exists, and every caller drops the commit
+ * rather than falling back to `selector` (see writeTargetSelector): the drag
+ * reverts on the next reload, which is recoverable, where a `.group` write is
+ * not.
  */
-function newTweenTarget(selection: DomEditSelection, selector: string): string {
-  return writeTargetSelector(selection) ?? selector;
+function newTweenTarget(selection: DomEditSelection): string | null {
+  return writeTargetSelector(selection);
 }
 
 // Re-export for backward compatibility with existing imports.
@@ -77,17 +82,18 @@ export function parkPlayheadOnKeyframe(anim: GsapAnimation, pct: number): void {
 
 async function replaceKeyframedPositionHold(
   selection: DomEditSelection,
-  selector: string,
   existingSet: GsapAnimation,
   properties: { x: number; y: number },
   commitMutation: GsapDragCommitCallbacks["commitMutation"],
 ): Promise<void> {
+  const target = newTweenTarget(selection);
+  if (!target) return;
   const persist = async (commit: GsapDragCommitCallbacks["commitMutation"]) => {
     await commit(
       selection,
       {
         type: "add",
-        targetSelector: newTweenTarget(selection, selector),
+        targetSelector: target,
         method: "set",
         position: 0,
         properties,
@@ -186,7 +192,6 @@ export async function commitStaticGsapPosition(
       // least one hold on disk, then delete the corrupt tween in one transaction.
       await replaceKeyframedPositionHold(
         selection,
-        selector,
         existingSet,
         { x: newX, y: newY },
         callbacks.commitMutation,
@@ -213,7 +218,8 @@ export async function commitStaticGsapPosition(
   // an instant patch so the first nudge shows immediately (no soft-reload flash).
   // The patch reuses the WRITTEN target so the runtime moves exactly the element
   // the source write names.
-  const target = newTweenTarget(selection, selector);
+  const target = newTweenTarget(selection);
+  if (!target) return;
   await callbacks.commitMutation(
     selection,
     {
@@ -270,7 +276,8 @@ export async function commitStaticGsapRotation(
     return;
   }
   // New static hold → off-timeline `gsap.set` (no 0% keyframe marker) + instant patch.
-  const target = newTweenTarget(selection, selector);
+  const target = newTweenTarget(selection);
+  if (!target) return;
   await callbacks.commitMutation(
     selection,
     {
@@ -323,11 +330,13 @@ export async function commitStaticGsapSize(
     );
     return;
   }
+  const target = newTweenTarget(selection);
+  if (!target) return;
   await callbacks.commitMutation(
     selection,
     {
       type: "add",
-      targetSelector: newTweenTarget(selection, selector),
+      targetSelector: target,
       method: "set",
       position: 0,
       properties: { width, height },
@@ -411,11 +420,13 @@ export async function commitKeyframedSizeFromResize(
   // transport applies both in one ordered batch; a plain commit fallback keeps the
   // same recoverable ordering. Only the transaction's result triggers the reload.
   const addLabel = `Resize (size keyframe ${pct.toFixed(0)}%)`;
+  const target = newTweenTarget(selection);
+  if (!target) return false;
   await callbacks.commitMutation(
     selection,
     {
       type: "add-with-keyframes",
-      targetSelector: newTweenTarget(selection, selector),
+      targetSelector: target,
       position: roundTo3(ts),
       duration: roundTo3(td),
       keyframes,

packages/studio/src/hooks/gsapKeyframeCommit.ts

@@ -63,16 +63,18 @@ export async function commitKeyframeAtTimeImpl(
       },
     );
   } else {
+    // Null means the live DOM could not prove any one-element form. Falling
+    // back to the author's own selector would write the group-collapsing
+    // target this narrowing exists to prevent, so the keyframe is dropped
+    // instead (see writeTargetSelector).
+    const target = writeTargetSelector(selection);
+    if (!target) return;
     const defaultDuration = 0.5;
     await commitMutation(
       selection,
       {
         type: "add-with-keyframes" as const,
-        // Null here means the live DOM could not prove any one-element form.
-        // This branch has no graceful no-op to fall to, so it takes the
-        // author's own selector, group collapse and all, over dropping the
-        // keyframe the user just asked for.
-        targetSelector: writeTargetSelector(selection) ?? selector,
+        targetSelector: target,
         position: absoluteTime,
         duration: defaultDuration,
         keyframes: [

packages/studio/src/hooks/gsapShared.ts

@@ -251,11 +251,12 @@ function structuralSelector(element: Element): string | null {
  * against, a failed structural walk (detached between select and commit, a
  * shadow-root boundary, a chain that no longer re-resolves) IS that evidence,
  * so returning the bare selector anyway would hand back the exact input this
- * function exists to replace. Callers decide what to do with the null: the
- * add-keyframe path has a graceful no-animation fallback, and the paths that
- * cannot afford to drop a user edit opt back in with `?? selectorFromSelection`
- * where the trade is visible. The bare selector comes back only with no DOM to
- * disambiguate against, where refusing would be guessing rather than knowing.
+ * function exists to replace. Every caller treats the null as "do not author
+ * this tween": falling back to the selection's own selector would write the
+ * group-collapsing target this function exists to prevent, and a gesture that
+ * does not persist reverts visibly on the next reload, where a tween silently
+ * aimed at five elements does not. The bare selector comes back only with no DOM
+ * to disambiguate against, where refusing would be guessing rather than knowing.
  */
 export function writeTargetSelector(selection: DomEditSelection): string | null {
   if (selection.id) return idSelector(selection.id);
@@ -298,8 +299,14 @@ export function existingTweenTargetSelector(
  * String equality against `selectorFromSelection` alone is not enough once new
  * tweens are authored with a narrowed one-element selector: the next edit would
  * miss the write it just made and append a second, conflicting one. Falling back
- * to the live DOM keeps the pair consistent, and still matches a deliberate group
- * tween (`.group` matches each of its siblings) so merges into it keep working.
+ * to the live DOM keeps the pair consistent.
+ *
+ * That fallback is `matchesExactlyOne`, not a bare `element.matches`. A target
+ * the element merely shares with its siblings is a GROUP tween, and the callers
+ * here MUTATE what they find: an individual nudge on one of five `.group`
+ * siblings would rewrite the group's own tween and move all five. Only the
+ * selection that IS the group (string equality above, where the author selected
+ * `.group` itself) may edit it; every other element authors its own write.
  */
 export function tweenTargetsElement(
   targetSelector: string,
@@ -307,13 +314,9 @@ export function tweenTargetsElement(
   element: Element | null | undefined,
 ): boolean {
   if (targetSelector === selector) return true;
-  if (!element) return false;
-  try {
-    return element.matches(targetSelector);
-  } catch {
-    // Not a selector `matches()` understands, so it never addressed this element.
-    return false;
-  }
+  const doc = element?.ownerDocument;
+  if (!element || !doc) return false;
+  return matchesExactlyOne(doc, targetSelector, element);
 }
 
 // ── Percentage computation ────────────────────────────────────────────────────

packages/studio/src/hooks/gsapShared.writeTarget.test.ts

@@ -4,7 +4,7 @@ import { parseGsapScript } from "@hyperframes/core/gsap-parser";
 import { addAnimationWithKeyframesToScript } from "@hyperframes/parsers/gsap-writer-acorn";
 import type { DomEditSelection } from "../components/editor/domEditingTypes";
 import { buildStableSelector, getSelectorIndex } from "../components/editor/domEditingDom";
-import { resolveSelectorElementIds, writeTargetSelector } from "./gsapShared";
+import { resolveSelectorElementIds, tweenTargetsElement, writeTargetSelector } from "./gsapShared";
 import { commitKeyframeAtTimeImpl } from "./gsapKeyframeCommit";
 import { promoteSetToKeyframes } from "./useEnableKeyframes";
 
@@ -244,3 +244,46 @@ describe("commitKeyframeAtTimeImpl — new-tween target", () => {
     expect(document.querySelector(mutation.targetSelector)).toBe(groups[3]);
   });
 });
+
+describe("tweenTargetsElement", () => {
+  it("matches a tween narrowed to this element by a selector the selection does not use", () => {
+    const groups = mountGroupSiblings();
+    groups[2]!.id = "narrowed";
+
+    // The write half authored "#narrowed"; the read half still has ".group".
+    expect(tweenTargetsElement("#narrowed", ".group", groups[2])).toBe(true);
+  });
+
+  it("does not hand an individual element the group tween it merely inherits", () => {
+    const groups = mountGroupSiblings();
+
+    // Selecting one sibling by its own address must not let an edit mutate the
+    // ".group" tween: that write moves all five, not the one being nudged.
+    expect(tweenTargetsElement(".group", "#scene > div:nth-child(3)", groups[2])).toBe(false);
+  });
+
+  it("still edits a group tween when the group itself is the selection", () => {
+    const groups = mountGroupSiblings();
+
+    expect(tweenTargetsElement(".group", ".group", groups[0])).toBe(true);
+  });
+
+  it("does not match a target that is not a selector matches() understands", () => {
+    const groups = mountGroupSiblings();
+
+    expect(tweenTargetsElement("div[unclosed", ".group", groups[0])).toBe(false);
+  });
+});
+
+describe("commitKeyframeAtTimeImpl — no one-element target", () => {
+  it("drops the keyframe rather than authoring the bare class", async () => {
+    const groups = mountGroupSiblings();
+    const selection = selectionFor(groups[3]!);
+    groups[3]!.remove();
+    const commitMutation = vi.fn(async () => undefined);
+
+    await commitKeyframeAtTimeImpl(selection, 1, [], { x: 12 }, commitMutation);
+
+    expect(commitMutation).not.toHaveBeenCalled();
+  });
+});

packages/studio/src/hooks/useAnimatedPropertyCommit.ts

@@ -214,7 +214,7 @@ async function commitStaticSet(
   }
   // Fresh adds don't reshape existing sets, so their ids can't go stale.
   for (const batch of newSetBatches) {
-    await addGlobalStaticSet(selection, batch, selector, commit);
+    await addGlobalStaticSet(selection, batch, commit);
   }
 }
 
@@ -244,16 +244,17 @@ function findGroupOwningStaticWrite(
 async function addGlobalStaticSet(
   selection: DomEditSelection,
   batch: [string, number | string][],
-  selector: string,
   commit: Commit,
 ): Promise<void> {
   const numericProps: SetPatchProps = {};
   for (const [k, v] of batch) {
     if (typeof v === "number") numericProps[k as keyof SetPatchProps] = v;
   }
-  // A brand-new write, so it must address ONE element: `selector` is the bare
-  // class an id-less selection yields, which would hold every sibling.
-  const target = writeTargetSelector(selection) ?? selector;
+  // A brand-new write, so it must address ONE element: the selection's own
+  // selector is the bare class an id-less element yields, which would hold every
+  // sibling. No one-element form means no write at all (see writeTargetSelector).
+  const target = writeTargetSelector(selection);
+  if (!target) return;
   await commit(
     selection,
     {
@@ -493,7 +494,11 @@ export function useAnimatedPropertyCommit(deps: CommitAnimatedPropertyDeps) {
         // contaminating a foreign-group tween. Mirror an existing keyframed tween's
         // time range so the new group animates over the same span. The 0% baseline is
         // an `_auto` endpoint so it tracks the nearest keyframe as you add more.
-        if (selector) {
+        // A fresh tween, so its target must address ONE element; with no
+        // one-element form the edit is dropped rather than written onto every
+        // class sibling (see writeTargetSelector).
+        const newTweenTarget = writeTargetSelector(selection);
+        if (selector && newTweenTarget) {
           const template = selectedGsapAnimations.find((a) => !!a.keyframes);
           const tStart = template ? (resolveTweenStart(template) ?? 0) : 0;
           const tDur = template ? resolveTweenDuration(template) || 1 : 1;
@@ -514,7 +519,7 @@ export function useAnimatedPropertyCommit(deps: CommitAnimatedPropertyDeps) {
             selection,
             {
               type: "add-with-keyframes",
-              targetSelector: writeTargetSelector(selection) ?? selector,
+              targetSelector: newTweenTarget,
               position: roundTo3(tStart),
               duration: roundTo3(tDur),
               keyframes,

packages/studio/src/hooks/useGestureCommit.ts

@@ -178,7 +178,14 @@ export function useGestureCommit({
         showToast("Cannot save — element has no selector", "error");
         return;
       }
-      const writeSelector = writeTargetSelector(sel) ?? selector;
+      // A recorded gesture becomes a NEW tween, so its target must address one
+      // element; the selection's own selector would record the motion onto
+      // every sibling sharing its class (see writeTargetSelector).
+      const writeSelector = writeTargetSelector(sel);
+      if (!writeSelector) {
+        showToast("Cannot save: element has no unique selector", "error");
+        return;
+      }
       if (liveSession.commitMutation) {
         const recStart = recordingStartTimeRef.current;
         const rawKeyframes = sortedPcts.map((pct) => ({