fix(studio): a timeline scrubs when its host omits sessionEpoch (#4742)

* fix(studio): a timeline scrubs when its host omits sessionEpoch

* fix(studio): drop the added comment for the comment ratchet

packages/studio/src/player/components/Timeline.rulerSeek.test.tsx

@@ -108,4 +108,11 @@ describe("Timeline ruler origin", () => {
     expect(origin).toBe("80px");
     expect(published).toBe("80");
   });
+
+  it("seeks on a press when the host omits sessionEpoch after a session began", async () => {
+    usePlayerStore.getState().beginTimelineSession("host-project");
+    expect(usePlayerStore.getState().timelineSessionEpoch).toBeGreaterThan(0);
+    const { time, tickTime } = await seekOnFirstTick({}, false);
+    expect(time).toBeCloseTo(tickTime, 1);
+  });
 });

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

@@ -66,7 +66,7 @@ export function useTimelineProviderState({
   showAudioEffects = true,
   showKeyframes = true,
   trackPadding,
-  sessionEpoch = 0,
+  sessionEpoch: sessionEpochProp,
   previewIframeRef,
   onZIndexReorder,
 }: TimelineProps = {}): TimelineContextValue {
@@ -108,6 +108,7 @@ export function useTimelineProviderState({
   const currentTime = usePlayerStore((s) => s.currentTime);
   const beatDragging = usePlayerStore((s) => s.beatDragging);
   const timelineSessionEpoch = usePlayerStore((s) => s.timelineSessionEpoch);
+  const sessionEpoch = sessionEpochProp ?? timelineSessionEpoch;
   const setFocusedEaseSegment = usePlayerStore((s) => s.setFocusedEaseSegment);
   const { zoomMode, manualZoomPercent, setZoomMode, setManualZoomPercent } = useTimelineZoom();
   const playheadRef = useRef<HTMLDivElement>(null);