fix(studio): half-lit group solo compares bare DOM ids too

A fifth face of the id-space mismatch, not in the review's list.
TimelineGroupRow built its member list from `el.key ?? el.id` and handed
it to isGroupHalfLitUnderSolo, which compares against the soloed set —
bare DOM ids now that the header pushes them that way. Soloing a member
lit nothing on its group, the one signal that says "some of what is
under here still plays".

Found by auditing every consumer of `soloed` rather than trusting the
handoff's claim that this call site "happens to pass the bare id" — it
passes a bare id for the GROUP and store keys for its MEMBERS.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/studio/src/player/components/TimelineGroupRow.tsx

@@ -1,6 +1,7 @@
 import type { TimelineElement } from "../store/playerStore";
 import { usePlayerStore } from "../store/playerStore";
 import { isGroupHalfLitUnderSolo } from "../store/audioSoloSlice";
+import { runtimeAudioId } from "../lib/timelineElementHelpers";
 import {
   HF_AUDIO_FX_ATTR,
   serializeAudioFxChain,
@@ -65,7 +66,10 @@ export function TimelineGroupRow({
   const domEditActions = useDomEditActionsContextOptional();
   const soloed = usePlayerStore((s) => s.soloed);
   const toggleSolo = usePlayerStore((s) => s.toggleSolo);
-  const memberIds = memberElements.map((el) => el.key ?? el.id);
+  // Bare DOM ids: this list is compared against the `soloed` set, which the
+  // runtime matches on `el.id` (see `runtimeAudioId`). Store keys here made the
+  // half-lit state unreachable — soloing a member lit nothing on its group.
+  const memberIds = memberElements.map(runtimeAudioId).filter((id): id is string => id !== null);
   const writeGroupFxChain = (next: HfAudioFxChain, live: boolean) => {
     const value = next.nodes.length ? serializeAudioFxChain(next) : null;
     if (live) onSetAudioGroupAttributeLive?.(group.id, HF_AUDIO_FX_ATTR, value);

packages/studio/src/player/lib/runtimeAudioId.test.ts

@@ -15,6 +15,7 @@ import { describe, expect, it } from "vitest";
 import {
   audioGroupOf,
   isAudibleUnderSolo,
+  isGroupHalfLitUnderSolo,
   resolveAudioGroups,
 } from "@hyperframes/core/audio-groups";
 import { parseTimelineFromDOM } from "./timelineDOM";
@@ -95,6 +96,24 @@ describe("group membership ids cross into the runtime", () => {
     for (const id of memberIds) expect(clipIds).toContain(id);
   });
 
+  // TimelineGroupRow's half-lit state ("some of what's under here still
+  // plays") compares its member list against the same soloed set. Built from
+  // store keys it never matched, so soloing a member lit nothing on its group.
+  it("half-lights the group when one member is soloed", () => {
+    const doc = docWith(COMPOSITION);
+    const members = parseTimelineFromDOM(doc, 30).filter((el) => el.audioGroup === "voiceover");
+    const memberIds = members.map(runtimeAudioId).filter((id): id is string => id !== null);
+    expect(memberIds).toEqual(["voice-1", "voice-2"]);
+
+    const soloed = new Set(["voice-1"]);
+    expect(isGroupHalfLitUnderSolo(soloed, "voiceover", memberIds)).toBe(true);
+    // Store keys are the shape that silently failed.
+    const storeKeys = members.map((el) => el.key ?? el.id);
+    expect(isGroupHalfLitUnderSolo(soloed, "voiceover", storeKeys)).toBe(false);
+    // Soloing the group itself is lit, not half-lit.
+    expect(isGroupHalfLitUnderSolo(new Set(["voiceover"]), "voiceover", memberIds)).toBe(false);
+  });
+
   it("an element with no DOM id is not groupable or soloable", () => {
     const doc = docWith(`
       <div data-composition-id="root" data-duration="10"></div>