repair(perf): preserve GrooveMap delta while removing stale branch drift

CHANGELOG.md

@@ -7,6 +7,10 @@
 - Display the analyzed song tempo (BPM) as a badge in the rehearsal workspace.
 - 각 합주 역할(Role)별 개인 연습 진행도를 0~100% 범위로 기록 및 시각화할 수 있는 연습 진척도(`practiceProgress`) 트래커 기능 추가. UI 컨트롤(슬라이더 및 +/- 버튼)과 한/영 다국어 지원 포함.
 
+### Changed
+
+- Preserve GrooveMap's ten-second timeline floor while computing larger transcription bounds with a single allocation-free loop.
+
 ## [0.1.3] - 2026-04-29
 
 ### Fixed

apps/desktop/src/features/workspace/GrooveMap.test.tsx

@@ -0,0 +1,35 @@
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+import { GrooveMap } from "./GrooveMap";
+
+describe("GrooveMap", () => {
+  it("uses the latest note offset as the timeline maximum when it exceeds the ten-second floor", () => {
+    render(
+      <GrooveMap
+        notes={[
+          { pitch: "E2", onset: 10, offset: 20, velocity: 0.8 },
+          { pitch: "G2", onset: 2, offset: 12, velocity: 0.7 }
+        ]}
+      />
+    );
+
+    const latestNote = screen.getByTitle("E2 (10.00s - 20.00s)");
+    const earlierNote = screen.getByTitle("G2 (2.00s - 12.00s)");
+
+    expect(latestNote.style.left).toBe("50%");
+    expect(latestNote.style.width).toBe("50%");
+    expect(earlierNote.style.left).toBe("10%");
+    expect(earlierNote.style.width).toBe("50%");
+  });
+
+  it("retains the ten-second timeline floor when every note ends earlier", () => {
+    render(
+      <GrooveMap notes={[{ pitch: "A2", onset: 2, offset: 5, velocity: 0.6 }]} />
+    );
+
+    const note = screen.getByTitle("A2 (2.00s - 5.00s)");
+
+    expect(note.style.left).toBe("20%");
+    expect(note.style.width).toBe("30%");
+  });
+});

apps/desktop/src/features/workspace/GrooveMap.tsx

@@ -17,7 +17,11 @@ function GrooveMapComponent({ notes, isLoading }: GrooveMapProps) {
 
   // Find max offset to determine timeline width
   const maxTime = useMemo(() => {
-    return renderedNotes.reduce((max, n) => Math.max(max, n.offset), 10);
+    let max = 10;
+    for (const n of renderedNotes) {
+      if (n.offset > max) max = n.offset;
+    }
+    return max;
   }, [renderedNotes]);
 
   // Unique pitches to determine vertical lanes (avoiding 88-key piano roll)