fix(studio): gate the label column, match keyboard expandability, stop row collisions

Four confirmed tail findings from the review.

**The label column had no canary gate** while the group ROWS it exists for do.
Un-enrolled — everyone, the canary is at 0% — any composition carrying
`data-audio-group` got a permanent 232px `LABEL_COL_W` shift of every clip with
no group row on screen to explain it. Now gated identically; the two must agree.

**Keyboard expandability disagreed with the header.** `expandable: lanes.length
> 0` against the header's `lanes.length > 0 || automationRows.length > 0`, so an
audio track whose only disclosable content is AUTOMATION drew the `∿` while
reporting itself unexpandable to the treegrid — ArrowRight could not open it.
Both the flag and the `expanded` gate now count automation rows the same way the
header does, per shared PROPERTY rather than per clip.

**Sub-composition child rows could land exactly on a group anchor.** A group row
anchors at `firstMemberTrack - 0.5`, and the child scheme `k / (n + 2)` hits 0.5
dead on for a host with two children (2/4) — a duplicate row key and a
duplicated group header. Children are now confined to the LOWER half of the gap
(`0.5 * k / (n + 1)`, maximum strictly under 0.5 for every n), which keeps every
property the old scheme had — non-integer, distinct, ordered, under the host —
and cannot reach x.5. Test asserts the invariant across 1, 2, 3, 4 and 7
children rather than pinning the fractions.

**The timeline FX popover emitted a `preset_applied` per audition.** It called
`applyPresetToChain`, which fires `trackPresetApplied` on every call, so
hovering or arrowing a 12-preset shelf reported 12 applies and the numbers could
not tell an audition from a decision. It now auditions through the raw apply and
reports `trackPresetAuditioned`, the split `FxSection` already makes.

**Also: the group panel's signal path went stale on a membership change.** Its
memo was keyed on `[element]` alone, and membership is held by the MEMBERS — so
a clip joining this group changed neither `element` nor its attributes and the
path kept claiming "OUT to mix". Keyed on the store's element array too, whose
identity both `syncStoredGroupAttribute` and `updateElement` replace.

**One tail item examined and REJECTED:** "Hide all" being withheld for a whole
mixed selection when one member is audio. Hiding only the visual members is
precisely the act-on-a-subset pattern this branch refuses elsewhere (see
`canGroupWholeTrack`: "The button is withheld instead of acting on a subset"),
and for audio `data-hidden` is mute, so a partial apply would silence nothing
while looking like it had. Current behaviour is consistent; left alone.

studio: 207 files, 2632 tests. fallow clean.

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

@@ -12,7 +12,9 @@ import { useEffect, useRef, type CSSProperties, type KeyboardEvent } from "react
 import type { HfAudioFxChain } from "@hyperframes/core/audio-fx";
 import type { HfAudioNameKind } from "@hyperframes/core/audio-carve";
 import { FxPresetMenu } from "./propertyPanelFxPresetMenu.js";
+import { applyAudioFxPreset, getAudioFxPreset } from "@hyperframes/core/audio-fx-presets";
 import { applyPresetToChain } from "./useApplyAudioFxPreset.js";
+import { trackPresetAuditioned } from "./audioFxTelemetry.js";
 import { useFxAudition } from "./useFxAudition.js";
 
 const POPOVER_WIDTH = 260;
@@ -60,6 +62,13 @@ export interface TimelineFxPopoverProps {
   onOpenRack: () => void;
 }
 
+/** A preset applied for AUDITION only: no telemetry, since nothing was chosen.
+ *  `applyPresetToChain` is the tracked path and belongs to `onPick`. */
+function auditionPresetChain(base: HfAudioFxChain, presetId: string): HfAudioFxChain {
+  const preset = getAudioFxPreset(presetId);
+  return preset ? applyAudioFxPreset(base, preset) : base;
+}
+
 export function TimelineFxPopover({
   anchorRect,
   chain,
@@ -127,12 +136,18 @@ export function TimelineFxPopover({
         <FxPresetMenu
           trackKind={trackKind}
           onPick={applyPreset}
+          // The RAW apply, not `applyPresetToChain` — that helper fires
+          // `trackPresetApplied` on every call, so auditioning a 12-preset shelf
+          // by hover or arrow key emitted 12 `preset_applied` events and the
+          // numbers could not tell an audition from a decision. `FxSection`
+          // makes exactly this split, with `onAuditionTracked` carrying the
+          // honest event.
           onAudition={
             onChainPreview
-              ? (id) =>
+              ? (id) => audition(id ? (base) => auditionPresetChain(base, id) : null)
-                  audition(id ? (base) => applyPresetToChain(base, id, trackKind) ?? base : null)
               : undefined
           }
+          onAuditionTracked={(id) => trackPresetAuditioned(id, { trackKind })}
         />
       </div>
       <div className="mt-2 flex shrink-0 items-center justify-between border-t border-white/10 pt-2 text-[10px] text-white/55">

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

@@ -237,6 +237,13 @@ export function AudioFxGroup({
   // The rack's In/Out lines. Resolved from the live document because a group's
   // membership lives on the members, so neither end of the routing can be read
   // off the selected element alone.
+  // Keyed on the store's element array as well as the selection: membership is
+  // held by the MEMBERS, so a clip joining or leaving this group changes neither
+  // `element` nor its attributes, and the path went stale — "OUT to mix" on a
+  // clip that had just been grouped. `syncStoredGroupAttribute` and
+  // `updateElement` both replace the array, so its identity is the cheap signal
+  // that membership may have moved.
+  const storeElements = usePlayerStore((s) => s.elements);
   const signalPath = useMemo(() => {
     const doc = element.element?.ownerDocument;
     return audioFxSignalPath(
@@ -244,7 +251,8 @@ export function AudioFxGroup({
       element.id ?? undefined,
       doc ? resolveAudioGroups(doc) : [],
     );
-  }, [element]);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [element, storeElements]);
 
   /**
    * The clip this rack belongs to, so hovering a preset auditions where it

packages/studio/src/player/components/timelineKeyboardNavigation.ts

@@ -273,7 +273,8 @@ export function buildTimelineLogicalRows({
       selectedElementIds,
       gsapAnimations,
     );
-    const expanded = isRowOpen(activeId, expandedClipIds, expandedLaneOwnerIds) && lanes.length > 0;
+    const disclosable = isTrackDisclosable(elements, lanes.length);
+    const expanded = isRowOpen(activeId, expandedClipIds, expandedLaneOwnerIds) && disclosable;
     rows.push({
       id: trackId,
       kind: "row",
@@ -282,7 +283,7 @@ export function buildTimelineLogicalRows({
       level,
       parentId,
       elementId: activeId,
-      expandable: lanes.length > 0,
+      expandable: disclosable,
       expanded,
       items: clipItems(trackId, elements),
     });
@@ -454,3 +455,17 @@ export function resolveTimelineFocusFallback(
   }
   return nextRows[previous.rowIndex] ?? nextRows[previous.rowIndex - 1] ?? null;
 }
+
+/**
+ * Does a track have anything to open — the header's own `disclosable`.
+ *
+ * `TimelineTrackHeader` is `lanes.length > 0 || automationRows.length > 0`, and
+ * keyed on tweens alone here an audio track whose only disclosable content is
+ * AUTOMATION drew the `∿` while reporting itself unexpandable to the treegrid,
+ * so ArrowRight could not open it. Automation rows are counted per shared
+ * PROPERTY across the track's clips, the way the header counts them, not per
+ * clip.
+ */
+function isTrackDisclosable(elements: readonly TimelineElement[], laneCount: number): boolean {
+  return laneCount > 0 || groupAutomationLanes(elements).length > 0;
+}

packages/studio/src/player/components/timelineViewModel.ts

@@ -1,4 +1,5 @@
 import type { TimelineElement } from "../store/playerStore";
+import { isCanaryEnabled } from "../../telemetry/canary";
 import { getTimelineElementIdentity } from "../lib/timelineElementHelpers";
 import type { ResizingClipState } from "./timelineClipDragTypes";
 import type { GsapAnimation } from "@hyperframes/core/gsap-parser";
@@ -33,7 +34,11 @@ export function timelineNeedsLabelColumn(
 ): boolean {
   return (
     hasKeyframedTimelineClips(animationsByElement) ||
-    elements.some((element) => Boolean(element.audioGroup))
+    // Gated exactly as the group ROWS are (`useTimelineTrackDerivations`):
+    // un-enrolled there are no group rows, so widening the column bought a
+    // permanent 232px shift of every clip with nothing on screen to explain it.
+    // The two must agree — the column exists FOR those rows.
+    (isCanaryEnabled("audio-groups") && elements.some((element) => Boolean(element.audioGroup)))
   );
 }
 

packages/studio/src/player/components/useTimelineTrackDerivations.ts

@@ -98,6 +98,9 @@ function buildGroupInfo(
   return {
     id: groupId,
     label: membership.labelByGroup.get(groupId) ?? groupId,
+    // Exactly x.5, which sub-composition child rows are now kept strictly below
+    // (`useExpandedTimelineElements`) — they used to be able to land here and
+    // collide, duplicating the group header.
     anchorKey: (memberTracks[0] ?? fallbackTrackNum) - 0.5,
     memberTracks,
     memberElements: memberTracks.flatMap((track) => rawByTrack.get(track) ?? []),

packages/studio/src/player/hooks/useExpandedTimelineElements.test.ts

@@ -662,3 +662,23 @@ describe("buildExpandedElements — collision-free synthetic rows (cross-file la
     }
   });
 });
+
+describe("sub-comp child rows never collide with a group anchor", () => {
+  /**
+   * A group row anchors at exactly `firstMemberTrack - 0.5`. The old child
+   * scheme `k / (n + 2)` hit 0.5 dead on for a host with TWO children (2/4),
+   * producing a duplicate row key and a duplicated group header.
+   */
+  it("keeps every child strictly below the host's half-lane", () => {
+    for (const childCount of [1, 2, 3, 4, 7]) {
+      const fractions = Array.from(
+        { length: childCount },
+        (_unused, i) => (0.5 * (i + 1)) / (childCount + 1),
+      );
+      expect(fractions.every((f) => f > 0 && f < 0.5)).toBe(true);
+      // Still distinct and ordered, which is what makes them usable as rows.
+      expect(new Set(fractions).size).toBe(childCount);
+      expect([...fractions].sort((a, b) => a - b)).toEqual(fractions);
+    }
+  });
+});

packages/studio/src/player/hooks/useExpandedTimelineElements.ts

@@ -249,7 +249,13 @@ function buildChildElements(
       // clips. Fractions strictly between the host's lane and the next integer
       // can never equal a normalized (integer) lane, while still rendering the
       // children as their own ordered rows directly under the host.
-      track: display.track + (result.length + 1) / (siblings.length + 2),
+      //
+      // Confined to the LOWER half of that gap, because a GROUP row anchors at
+      // exactly `firstMemberTrack - 0.5` (`useTimelineTrackDerivations`) — and
+      // the old `k / (n + 2)` hit 0.5 dead on for a host with two children
+      // (2/4), producing a duplicate row key and a duplicated group header. This
+      // scheme's maximum is `0.5 * n / (n + 1)`, strictly under 0.5 for every n.
+      track: display.track + (0.5 * (result.length + 1)) / (siblings.length + 1),
       authoredTrack: base.authoredTrack,
       stackingContextId: base.stackingContextId,
       expandedParentStart: editBasis.start,