diff --git a/frontend/src/lib/components/HandwriteCanvas.svelte b/frontend/src/lib/components/HandwriteCanvas.svelte
index a471798..0a64008 100644
--- a/frontend/src/lib/components/HandwriteCanvas.svelte
+++ b/frontend/src/lib/components/HandwriteCanvas.svelte
@@ -77,6 +77,10 @@
   let effectiveSize = $derived(baseSize * WIDTH_FACTOR[widthMode]);
   let eraserRadius = $derived(Math.max(16, effectiveSize * 4));
 
+  // 지우개 이동 경로의 직전 점. pointerdown 에서 set, pointermove 에서 segment
+  // 시작점, end 에서 null. $state 아님 — 입력 루프 내부 값 (UI 미참조).
+  let eraserLast: [number, number] | null = null;
+
   let isDirty = false;
   let saveTimer: number | null = null;
   let snapshotting = $state(false);
@@ -235,7 +239,33 @@
     target.points.push([x, y, p]);
   }
 
-  function eraseAt(x: number, y: number): boolean {
+  // 점 P 와 선분 [A, B] 사이 최단 거리의 제곱. 빠른 비교를 위해 sqrt 안 씀.
+  function distSqPointToSegment(
+    px: number, py: number,
+    ax: number, ay: number, bx: number, by: number,
+  ): number {
+    const dx = bx - ax;
+    const dy = by - ay;
+    const lenSq = dx * dx + dy * dy;
+    if (lenSq === 0) {
+      const ex = px - ax;
+      const ey = py - ay;
+      return ex * ex + ey * ey;
+    }
+    let t = ((px - ax) * dx + (py - ay) * dy) / lenSq;
+    if (t < 0) t = 0;
+    else if (t > 1) t = 1;
+    const ex = px - (ax + t * dx);
+    const ey = py - (ay + t * dy);
+    return ex * ex + ey * ey;
+  }
+
+  // 지우개 이동 경로 [A, B] 위에 stroke 점이 eraserRadius 이내로 들어오면 해당
+  // stroke 통째 삭제 (object eraser). 단일 점 검사가 아니라 segment 검사라 빠른
+  // 지우개 이동에서 점 사이 stroke 누락 방지. A == B 면 단일 점 검사로 환원.
+  function eraseSegment(
+    x0: number, y0: number, x1: number, y1: number,
+  ): boolean {
     if (strokes.length === 0) return false;
     const r2 = eraserRadius * eraserRadius;
     const removed: Stroke[] = [];
@@ -243,9 +273,10 @@
     for (const s of strokes) {
       let hit = false;
       for (const [px, py] of s.points) {
-        const dx = px - x;
-        const dy = py - y;
-        if (dx * dx + dy * dy <= r2) { hit = true; break; }
+        if (distSqPointToSegment(px, py, x0, y0, x1, y1) <= r2) {
+          hit = true;
+          break;
+        }
       }
       (hit ? removed : keep).push(s);
     }
@@ -279,7 +310,8 @@
     const [x, y] = getLocalXY(e);
 
     if (tool === 'eraser') {
-      if (eraseAt(x, y)) {
+      eraserLast = [x, y];
+      if (eraseSegment(x, y, x, y)) {
         isDirty = true;
         backup();
         scheduleSave();
@@ -310,12 +342,14 @@
     const [x, y] = getLocalXY(e);
 
     if (tool === 'eraser') {
-      if (eraseAt(x, y)) {
+      const prev = eraserLast ?? [x, y];
+      if (eraseSegment(prev[0], prev[1], x, y)) {
         isDirty = true;
         backup();
         scheduleSave();
         scheduleRedraw();
       }
+      eraserLast = [x, y];
       return;
     }
 
@@ -339,7 +373,8 @@
   // pointerup → 정상 finalize. pointercancel → inflight 폐기 (사용자 의도가 아닌
   // OS 강제 취소 — multi-touch / 시스템 gesture 인식 시 발생. cancel 된 stroke 가
   // strokes 에 들어가면 의도치 않은 짧은 노이즈 stroke 누적, 사용자 글자 망가짐).
-  // pointerleave 는 무시 — stale leave 가 진행 중 stroke 끊는 케이스 방어.
+  // pointerleave 는 핸들러 미바인딩 — setPointerCapture 가 잡히면 leave 자체가 안
+  // 오고, 캡처 실패 케이스는 OS 가 pointercancel 로 흘려보냄.
   function endStroke(e: PointerEvent) {
     if (e.type === 'pointerup') dbg = { ...dbg, up: dbg.up + 1 };
     else if (e.type === 'pointercancel') dbg = { ...dbg, cancel: dbg.cancel + 1 };
@@ -357,6 +392,7 @@
 
     if (tool === 'eraser') {
       inflight = null;
+      eraserLast = null;
       return;
     }
 
@@ -584,20 +620,21 @@
       onpointermove={onPointerMove}
       onpointerup={endStroke}
       onpointercancel={endStroke}
-      onpointerleave={endStroke}
       oncontextmenu={(e) => e.preventDefault()}
       onselectstart={(e) => e.preventDefault()}
       class="block"
       style="touch-action: none; user-select: none; -webkit-user-select: none; -webkit-touch-callout: none; -webkit-tap-highlight-color: transparent; cursor: {tool === 'eraser' ? 'cell' : 'crosshair'};"
     ></canvas>
 
-    <!-- 라이브 디버그 패널 — 사용자가 어떤 이벤트가 들어오고 어디서 거부되는지 직접 확인 -->
-    <div class="absolute top-1 left-1 px-2 py-1 rounded bg-bg/90 text-[10px] text-dim font-mono pointer-events-none leading-tight">
-      type:{dbg.lastType} p:{dbg.lastPressure.toFixed(2)}<br/>
-      down:{dbg.down} move:{dbg.move} up:{dbg.up} cancel:{dbg.cancel}<br/>
-      rejType:{dbg.rejectedByType} rejId:{dbg.rejectedByPointerId} coal:{dbg.coalesced}<br/>
-      drawing:{isDrawing ? 'Y' : 'N'} actId:{activePointerId ?? '-'} infPts:{dbgInflightPts}<br/>
-      strokes:{strokes.length}
-    </div>
+    {#if import.meta.env.DEV}
+      <!-- 라이브 디버그 패널 — DEV 빌드 한정. prod 에선 Vite 가 dead-code-eliminate. -->
+      <div class="absolute top-1 left-1 px-2 py-1 rounded bg-bg/90 text-[10px] text-dim font-mono pointer-events-none leading-tight">
+        type:{dbg.lastType} p:{dbg.lastPressure.toFixed(2)}<br/>
+        down:{dbg.down} move:{dbg.move} up:{dbg.up} cancel:{dbg.cancel}<br/>
+        rejType:{dbg.rejectedByType} rejId:{dbg.rejectedByPointerId} coal:{dbg.coalesced}<br/>
+        drawing:{isDrawing ? 'Y' : 'N'} actId:{activePointerId ?? '-'} infPts:{dbgInflightPts}<br/>
+        strokes:{strokes.length}
+      </div>
+    {/if}
   </div>
 </div>
diff --git a/frontend/src/routes/study/write/[id]/+page.svelte b/frontend/src/routes/study/write/[id]/+page.svelte
index f64552b..90206b7 100644
--- a/frontend/src/routes/study/write/[id]/+page.svelte
+++ b/frontend/src/routes/study/write/[id]/+page.svelte
@@ -189,7 +189,9 @@
         {sess.study_type === 'language' ? `${sess.language_code || '?'} · ${sess.learning_level || ''}` : (sess.certification || '자격증')}
         · {sess.subject || ''} · {sess.topic || ''}
       {/if}
-      <span class="ml-2 text-[10px] text-dim/60">build {__BUILD_TIME__}</span>
+      {#if import.meta.env.DEV}
+        <span class="ml-2 text-[10px] text-dim/60">build {__BUILD_TIME__}</span>
+      {/if}
     </div>
 
     <button