diff --git a/B08_Quantity/B08_Quantity_Engine_StructureLibrary.py b/B08_Quantity/B08_Quantity_Engine_StructureLibrary.py
index 2e730dae..ff5f1979 100644
--- a/B08_Quantity/B08_Quantity_Engine_StructureLibrary.py
+++ b/B08_Quantity/B08_Quantity_Engine_StructureLibrary.py
@@ -19,8 +19,9 @@ from typing import Any
 from B08_Quantity.B08_Quantity_Engine_StructureTemplate import TEMPLATE_DIR
 from config.config_system import STORAGE_BASE_DIR
 
-#: 단 이름 — 고르개에 이 차례로 보임(가까운 것부터).
-TIERS = ("personal", "company", "program")
+#: 단 이름 — 고르개에 이 차례로 보임(가까운 것부터). `received` = 동료가 보낸 것(공유 · 개인 단을 안 덮음).
+TIERS = ("personal", "received", "company", "program")
+RECEIVED_SUBDIR = "library_received"
 #: 항목 코드 — 파일 이름이 되므로 모양을 먼저 봄(경로 벗어남 막이).
 CODE_PATTERN = re.compile(r"^AX-ST-[0-9a-f]{8}$")
 LIBRARY_SUBDIR = "library"
@@ -55,6 +56,7 @@ def tier_dirs(company_id: Any, user_id: Any) -> dict[str, Path]:
         company = Path(STORAGE_BASE_DIR).resolve() / str(company_id)
         if user_id is not None:
             dirs["personal"] = company / str(user_id) / LIBRARY_SUBDIR
+            dirs["received"] = company / str(user_id) / RECEIVED_SUBDIR
         dirs["company"] = company / LIBRARY_SUBDIR
     dirs["program"] = program_library_dir()
     return dirs
@@ -230,3 +232,13 @@ def pin_program_templates(project_root: str | Path) -> int:
             import_item(project_root, item, "program")
             count += 1
     return count
+
+
+def share_item(item: dict[str, Any], to_folder: Path, sender: dict[str, Any]) -> str:
+    """[동료에게 보내기] — 내 개인 단 항목을 동료의 **받음 단**에 복사(개인 단을 안 덮음 · 브레인 판정 ①).
+
+    코드는 그대로(다시 보내면 같은 자리를 새로 씀) · 출처 공사명도 그대로(같은 회사 · 판정 ③).
+    """
+    body = {k: v for k, v in item.items() if k != "imported_from"}
+    _write(to_folder, {**body, "library_tier": "received", "received_from": sender})
+    return str(body["code"])
diff --git a/B08_Quantity/B08_Quantity_Router_StmateLibrary.py b/B08_Quantity/B08_Quantity_Router_StmateLibrary.py
index 604fba01..6162be00 100644
--- a/B08_Quantity/B08_Quantity_Router_StmateLibrary.py
+++ b/B08_Quantity/B08_Quantity_Router_StmateLibrary.py
@@ -121,7 +121,7 @@ class LibraryCloneRequest(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
     type_id: str = Field(min_length=1, max_length=100)
-    tier: Literal["company", "program"]
+    tier: Literal["received", "company", "program"]
     code: str = Field(pattern=r"^AX-ST-[0-9a-f]{8}$")
 
 
@@ -149,3 +149,71 @@ async def clone_library_item(
     body["cloned_from"] = {"tier": payload.tier, "code": payload.code, "name": item.get("name")}
     code = await asyncio.to_thread(save_item_personal, folder, body)
     return JSONResponse(content={"status": "success", "code": code, "name": item.get("name")})
+
+
+async def _company_members(company_id: int) -> list[dict[str, Any]]:
+    """같은 회사 구성원 — B01 구성원 저장소를 읽기만(시험이 갈아 끼움)."""
+    from B01_Dashboard.B01_Dashboard_Repository_Members import list_company_members
+
+    return await list_company_members(company_id)
+
+
+@router.get("/{project_id}/quantity/structure-sheets/library/colleagues")
+async def list_library_colleagues(
+    project_id: UUID, session: dict[str, Any] = Depends(verify_session)
+) -> JSONResponse:
+    """④ 보낼 동료 — 같은 회사에서 나를 뺀 사람(이름만)."""
+    company_id = session.get("company_id")
+    if company_id is None:
+        return _error(403, "회사에 속한 사용자만 보냅니다.")
+    members = await _company_members(int(company_id))
+    colleagues = [
+        {"id": m["id"], "name": m.get("name") or m.get("email") or ""}
+        for m in members
+        if m["id"] != session.get("user_id")
+    ]
+    return JSONResponse(content={"status": "success", "colleagues": colleagues})
+
+
+class LibraryShareRequest(BaseModel):
+    """내 개인 단 항목 하나를 같은 회사 동료에게."""
+
+    model_config = ConfigDict(extra="forbid")
+
+    type_id: str = Field(min_length=1, max_length=100)
+    code: str = Field(pattern=r"^AX-ST-[0-9a-f]{8}$")
+    to_user_id: int
+
+
+@router.put("/{project_id}/quantity/structure-sheets/library/share")
+async def share_library_item(
+    project_id: UUID,
+    payload: LibraryShareRequest,
+    session: dict[str, Any] = Depends(verify_session),
+) -> JSONResponse:
+    """④ [동료에게 보내기] — 받는 쪽 「받음」 단에 복사(PLAN 4장 공유 · 브레인 판정 ①)."""
+    from B08_Quantity.B08_Quantity_Engine_StructureLibrary import (
+        RECEIVED_SUBDIR,
+        find_item,
+        share_item,
+        tier_dirs,
+    )
+
+    company_id = session.get("company_id")
+    dirs = tier_dirs(company_id, session.get("user_id"))
+    if "personal" not in dirs:
+        return _error(403, "회사에 속한 사용자만 보냅니다.")
+    if payload.to_user_id == session.get("user_id"):
+        return _error(400, "나에게는 보내지 않습니다.")
+    members = {m["id"]: m for m in await _company_members(int(company_id))}
+    target = members.get(payload.to_user_id)
+    if target is None:
+        return _error(404, "같은 회사에서 받는 사람을 찾지 못했습니다.")
+    item = await asyncio.to_thread(find_item, dirs, "personal", payload.code)
+    if item is None or item.get("type_id") != payload.type_id:
+        return _error(404, "보낼 내 항목을 찾지 못했습니다.")
+    me = members.get(session.get("user_id")) or {}
+    sender = {"user_id": session.get("user_id"), "name": me.get("name") or me.get("email") or ""}
+    to_folder = dirs["personal"].parents[1] / str(payload.to_user_id) / RECEIVED_SUBDIR
+    code = await asyncio.to_thread(share_item, item, to_folder, sender)
+    return JSONResponse(content={"status": "success", "code": code, "to": target.get("name") or ""})
diff --git a/B08_Quantity/B08_Quantity_Router_StructureSheet.py b/B08_Quantity/B08_Quantity_Router_StructureSheet.py
index f3128559..0a66b219 100644
--- a/B08_Quantity/B08_Quantity_Router_StructureSheet.py
+++ b/B08_Quantity/B08_Quantity_Router_StructureSheet.py
@@ -327,7 +327,7 @@ class LibraryImportRequest(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
     type_id: str = Field(min_length=1, max_length=100)
-    tier: Literal["personal", "company", "program"]
+    tier: Literal["personal", "received", "company", "program"]
     code: str = Field(pattern=r"^AX-ST-[0-9a-f]{8}$")
 
 
diff --git a/B08_Quantity/B08_Quantity_UI_StructureSheet_Library.ts b/B08_Quantity/B08_Quantity_UI_StructureSheet_Library.ts
index 8ef3da1e..470c86d5 100644
--- a/B08_Quantity/B08_Quantity_UI_StructureSheet_Library.ts
+++ b/B08_Quantity/B08_Quantity_UI_StructureSheet_Library.ts
@@ -10,7 +10,12 @@
 import { API_BASE_URL } from "@config/config_frontend";
 import { buildStmatePanel } from "./B08_Quantity_UI_StructureSheet_Stmate";
 
-const TIER_LABELS: Record<string, string> = { personal: "개인", company: "회사", program: "기본" };
+const TIER_LABELS: Record<string, string> = {
+  personal: "개인",
+  received: "받음",
+  company: "회사",
+  program: "기본",
+};
 /** 항목 종류 배지 — 양식형 = 제원을 바꾸면 수량이 다시 남 · 고정형 = 박힌 수량(명세 13장). */
 const KIND_LABELS: Record<string, string> = { form: "양식형", fixed: "고정형" };
 
@@ -90,10 +95,63 @@ export function buildLibraryPanel(options: LibraryPanelOptions): HTMLElement {
   clone.hidden = true;
   /** 목록을 다시 받은 뒤 보일 한 줄 — 받는 동안 상태 줄이 지워져 복제 결과가 사라지지 않게. */
   let afterLoad = "";
+  // 공유 — 내 개인 단 항목을 같은 회사 동료의 「받음」 단으로(브레인 판정 ①). 동료는 누를 때 받음.
+  const send = document.createElement("button");
+  send.type = "button";
+  send.className = "b08-quantity__tab";
+  send.textContent = "동료에게 보내기";
+  send.hidden = true;
+  const who = document.createElement("select");
+  who.className = "b08-spec__input";
+  who.hidden = true;
   const syncClone = (): void => {
     const [tier] = list.value.split("|");
     clone.disabled = tier === "personal";
+    send.disabled = tier !== "personal";
   };
+  send.addEventListener("click", () => {
+    const [tier, code] = list.value.split("|");
+    if (tier !== "personal" || !code) return;
+    void (async () => {
+      send.disabled = true;
+      try {
+        if (who.hidden) {
+          const { colleagues } = await readJson<{ colleagues: { id: number; name: string }[] }>(
+            await fetch(libraryUrl(projectId, "/colleagues"), { credentials: "include" }),
+          );
+          who.replaceChildren(...colleagues.map((c) => new Option(c.name, String(c.id))));
+          who.hidden = colleagues.length === 0;
+          status.textContent = colleagues.length
+            ? "받을 동료를 고르고 한 번 더 누를 것"
+            : "보낼 동료가 없음";
+          return;
+        }
+        const label = list.selectedOptions[0]?.textContent ?? "";
+        const name = who.selectedOptions[0]?.textContent ?? "";
+        if (
+          !window.confirm(
+            `「${label}」을 ${name}에게 보냄 — 받는 쪽 목록에 「받음」으로 뜸 · 그 사람 것은 안 덮음`,
+          )
+        ) {
+          return;
+        }
+        await readJson(
+          await fetch(libraryUrl(projectId, "/share"), {
+            method: "PUT",
+            credentials: "include",
+            headers: { "Content-Type": "application/json" },
+            body: JSON.stringify({ type_id: typeId, code, to_user_id: Number(who.value) }),
+          }),
+        );
+        who.hidden = true;
+        status.textContent = `${name}에게 보냄`;
+      } catch (error) {
+        status.textContent = error instanceof Error ? error.message : "보내지 못함";
+      } finally {
+        syncClone();
+      }
+    })();
+  });
   list.addEventListener("change", syncClone);
   clone.addEventListener("click", () => {
     const [tier, code] = list.value.split("|");
@@ -149,7 +207,7 @@ export function buildLibraryPanel(options: LibraryPanelOptions): HTMLElement {
             return option;
           }),
         );
-        list.hidden = take.hidden = clone.hidden = items.length === 0;
+        list.hidden = take.hidden = clone.hidden = send.hidden = items.length === 0;
         syncClone();
         // 발행 단추 — 서버가 준 권한대로만 보임(회사 = 마스터 · 기본 = 시스템 관리자).
         toCompany.hidden = !canPublish?.company;
@@ -275,7 +333,7 @@ export function buildLibraryPanel(options: LibraryPanelOptions): HTMLElement {
   mine.className = "b08-sheet__actions";
   mine.append(save, remove, toCompany, toProgram);
 
-  panel.append(title, scope, load, list, take, clone, mine, status);
+  panel.append(title, scope, load, list, take, clone, send, who, mine, status);
   // 고정형 항목을 만드는 둘째 길 — STmate 출력 엑셀에서 호표 하나를 뽑아 개인 단에(PLAN 4장).
   panel.append(
     buildStmatePanel({
diff --git a/resources/tester/test_b08_library_share.py b/resources/tester/test_b08_library_share.py
new file mode 100644
index 00000000..47feb08c
--- /dev/null
+++ b/resources/tester/test_b08_library_share.py
@@ -0,0 +1,108 @@
+"""라이브러리 공유 — 같은 회사 동료에게 내 항목을 복사해 보냄 (PLAN 4장 · 2026-09-14 브레인 판정 ①).
+
+⚠ 받는 쪽이 모르게 들어가지 않음 — 받은 항목은 그 사람 개인 단을 덮지 않고 **「받음」 단**에 따로 섬
+  (개인 단은 종류당 하나라 그대로 넣으면 동료가 고친 내 것이 조용히 덮임). 받은 뒤 가져오기·복제는 받는 사람 몫.
+⚠ 같은 회사 안만 · 출처 공사명은 그대로(같은 회사라 그 공사를 앎 · 판정 ③).
+"""
+
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+ROOT = Path(__file__).resolve().parents[2]
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+import B08_Quantity.B08_Quantity_Engine_StructureLibrary as library_module  # noqa: E402
+import B08_Quantity.B08_Quantity_Router_StmateLibrary as router_module  # noqa: E402
+from B08_Quantity.B08_Quantity_Engine_StructureTemplate import load_template  # noqa: E402
+from common_util.common_util_auth import verify_session  # noqa: E402
+
+LIB = "/api/projects/33333333-3333-3333-3333-333333333333/quantity/structure-sheets/library"
+MINE = "AX-ST-0000aaaa"
+
+
+@pytest.fixture()
+def client(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> TestClient:
+    monkeypatch.setattr(library_module, "STORAGE_BASE_DIR", str(tmp_path / "storage"))
+    item = {
+        **load_template("masonry_wet"),
+        "code": MINE,
+        "library_tier": "personal",
+        "name": "내 돌쌓기",
+        "origin": {"project": "봉화 임도"},
+    }
+    folder = tmp_path / "storage" / "7" / "42" / "library"
+    folder.mkdir(parents=True)
+    (folder / f"{MINE}.json").write_text(json.dumps(item), encoding="utf-8")
+    # 받는 사람(43)도 같은 종류 내 것이 있음 — 덮이면 안 됨
+    theirs = tmp_path / "storage" / "7" / "43" / "library"
+    theirs.mkdir(parents=True)
+    (theirs / "AX-ST-0000bbbb.json").write_text(
+        json.dumps({**item, "code": "AX-ST-0000bbbb", "name": "동료 것"}), encoding="utf-8"
+    )
+
+    async def members(company_id: int) -> list[dict]:
+        assert company_id == 7
+        return [
+            {"id": 42, "name": "나", "email": "me@x"},
+            {"id": 43, "name": "동료", "email": "you@x"},
+        ]
+
+    monkeypatch.setattr(router_module, "_company_members", members)
+    app = FastAPI()
+    app.include_router(router_module.router)
+    app.dependency_overrides[verify_session] = lambda: {"company_id": 7, "user_id": 42}
+    return TestClient(app)
+
+
+def test_동료_목록은_같은_회사에서_나를_뺀다(client: TestClient) -> None:
+    body = client.get(f"{LIB}/colleagues").json()
+    assert body["colleagues"] == [{"id": 43, "name": "동료"}]
+
+
+def test_보내면_받는_쪽_받음_단에_서고_그_사람_개인_단은_안_덮인다(
+    client: TestClient, tmp_path: Path
+) -> None:
+    sent = client.put(
+        f"{LIB}/share", json={"type_id": "masonry_wet", "code": MINE, "to_user_id": 43}
+    )
+    assert sent.status_code == 200, sent.text
+    received = tmp_path / "storage" / "7" / "43" / "library_received" / f"{MINE}.json"
+    saved = json.loads(received.read_text(encoding="utf-8"))
+    assert saved["library_tier"] == "received"
+    assert saved["received_from"]["name"] == "나" and saved["origin"]["project"] == "봉화 임도"
+    theirs = tmp_path / "storage" / "7" / "43" / "library" / "AX-ST-0000bbbb.json"
+    assert json.loads(theirs.read_text(encoding="utf-8"))["name"] == "동료 것"
+    dirs = library_module.tier_dirs(7, 43)
+    listed = library_module.list_items(dirs, "masonry_wet")
+    assert [i["tier"] for i in listed][:2] == ["personal", "received"]
+
+
+def test_회사_밖이나_내_것_아닌_항목은_못_보낸다(client: TestClient) -> None:
+    stranger = client.put(
+        f"{LIB}/share", json={"type_id": "masonry_wet", "code": MINE, "to_user_id": 99}
+    )
+    assert stranger.status_code == 404
+    missing = client.put(
+        f"{LIB}/share", json={"type_id": "masonry_wet", "code": "AX-ST-0000cccc", "to_user_id": 43}
+    )
+    assert missing.status_code == 404
+    myself = client.put(
+        f"{LIB}/share", json={"type_id": "masonry_wet", "code": MINE, "to_user_id": 42}
+    )
+    assert myself.status_code == 400
+
+
+def test_화면에_보내기_단추와_받음_표시() -> None:
+    ui = (ROOT / "B08_Quantity" / "B08_Quantity_UI_StructureSheet_Library.ts").read_text(
+        encoding="utf-8"
+    )
+    assert "/share" in ui and "/colleagues" in ui and "동료에게 보내기" in ui
+    assert 'received: "받음"' in ui