diff --git a/A00_Common/design/design_save.ts b/A00_Common/design/design_save.ts
index 0bf05bfba..a9ed7fc15 100644
--- a/A00_Common/design/design_save.ts
+++ b/A00_Common/design/design_save.ts
@@ -101,17 +101,23 @@ export function noticeDroppedEdits(saved: { dropped_edit_chainages?: number[] })
   );
 }
 
+/** 노선 초안 동안의 계획고 초안 칸 — `design_pipeline_page` 의 `DRAFT_ROUTE_ID` 와 같은 값(sub7). */
+const DRAFT_ROUTE_ID = 0;
+
 /** 계획고 초안(가게 하나)을 종단 정본에 쓴다. 없으면 아무 일도 하지 않는다. 노선이 바뀌었으면
- *  옛 노선 칸(`from`)의 초안을 새 노선(`routeId`)에 — 측점이 없는 자리는 서버가 버리고 알림(213-2). */
+ *  노선 초안 칸(`DRAFT_ROUTE_ID`) · 없으면 옛 노선 칸(`from`)의 초안을 새 노선(`routeId`)에 · 두 칸 다
+ *  비움 — 측점이 없는 자리는 서버가 버리고 알림(213-2). */
 async function flushAlignmentDraft(
   projectId: string,
   routeId: number,
   from: number = routeId,
 ): Promise<void> {
-  const draft = pendingAlignment(from);
+  const moved = from !== routeId;
+  const draft = (moved ? pendingAlignment(DRAFT_ROUTE_ID) : null) ?? pendingAlignment(from);
   if (!draft) return;
   noticeDroppedEdits(await saveProfileAlignment(projectId, routeId, draft));
   markAlignmentSaved(from);
+  if (moved) markAlignmentSaved(DRAFT_ROUTE_ID);
 }
 
 /** 실패해도 다음 차례로 넘어가는 창구와 그 이름(보기가 준 일에도 같이 씌운다). */
diff --git a/resources/tester/helper_design_store_save.cjs b/resources/tester/helper_design_store_save.cjs
index 69c680c36..419c6aa70 100644
--- a/resources/tester/helper_design_store_save.cjs
+++ b/resources/tester/helper_design_store_save.cjs
@@ -225,6 +225,21 @@ async function run() {
     { confirm: true },
   );
   out.routeConfirmCalls = [...calls];
+  // ⑨ 노선 초안 동안 계획고 = 노선 0 칸(sub7 DRAFT_ROUTE_ID) — 그 칸이 새 노선에 나가고 두 칸 다 비움
+  b05.replace({ station_offsets: { "30.000": 0.2 }, curve_radii: {} }); // 옛 노선(7) 초안
+  useDesignStore(null, 0).set("alignmentDraft", {
+    station_offsets: { "35.000": 0.4 },
+    curve_radii: {},
+  });
+  calls.length = 0;
+  await saveDesign({
+    projectId: "p1",
+    routeId: () => 7,
+    cross: async (confirm) => calls.push(`cross:${confirm}`),
+    failed: () => calls.push("failed"),
+  });
+  out.draftRouteCalls = calls.filter((c) => c.startsWith("alignment:"));
+  out.draftRouteLeft = { draft: edit.pendingAlignment(0), old: edit.pendingAlignment(7) };
   routeBody = null;
 
   // ⑤ [초기화] — 초안 · 한 벌 모두 버림
diff --git a/resources/tester/test_design_store_save.py b/resources/tester/test_design_store_save.py
index b868f21e4..59295fe34 100644
--- a/resources/tester/test_design_store_save.py
+++ b/resources/tester/test_design_store_save.py
@@ -126,3 +126,17 @@ def test_확정_중_노선이_바뀌면_다시_세우고_확정은_다시(out):
     calls = out["routeConfirmCalls"]
     assert calls[1] == "route" and calls[-2:] == ["rebuild", "overlay:off"]
     assert "done:true" not in calls and "cross:true" not in calls
+
+
+def test_노선_초안_칸_계획고가_새_노선으로(out):
+    """346-3 덧 — 노선 초안 동안 계획고는 노선 0 칸(sub7) · 노선 저장 뒤 그 칸이 새 노선 9 로 · 0 · 7 칸 다 비움."""
+    assert out["draftRouteCalls"] == ['alignment:9:{"35.000":0.4}']
+    assert out["draftRouteLeft"] == {"draft": None, "old": None}
+    design = os.path.join(HERE, "..", "..", "A00_Common", "design")
+    with open(os.path.join(design, "design_pipeline_page.ts"), encoding="utf-8") as f:
+        pipeline = f.read()
+    with open(os.path.join(design, "design_save.ts"), encoding="utf-8") as f:
+        save = f.read()
+    assert "const DRAFT_ROUTE_ID = 0;" in save
+    if "export const DRAFT_ROUTE_ID" in pipeline:  # 합친 뒤 — 두 값이 같아야 함
+        assert "export const DRAFT_ROUTE_ID = 0;" in pipeline