diff --git a/backend/app/api/endpoints/accounts.py b/backend/app/api/endpoints/accounts.py
index 0e0f457f..ea2e8624 100644
--- a/backend/app/api/endpoints/accounts.py
+++ b/backend/app/api/endpoints/accounts.py
@@ -21,7 +21,7 @@ from app.models.subscription import Subscription
 from app.models.user import User
 from app.schemas.account import AccountResponse, AccountUpdate, AccountInviteCreate, AccountInviteResponse, AccountInviteBulkCreate, AccountInviteBulkResponse, TransferOwnershipRequest
 from app.schemas.subscription import SubscriptionResponse, PlanLimitsResponse, UsageResponse, SubscriptionDetails
-from app.schemas.user import UserResponse, AccountRoleUpdate
+from app.schemas.user import UserResponse, AccountRoleUpdate, CoverageUpdate
 from app.core.security import verify_password
 from app.api.deps import get_current_active_user, require_account_owner, require_engineer_or_admin
 from app.services.seat_enforcement import check_seat_available, get_seat_usage
@@ -228,6 +228,43 @@ async def update_member_role(
     return user
 
 
+@router.patch("/me/members/{user_id}/coverage", response_model=UserResponse)
+async def update_member_coverage(
+    user_id: UUID,
+    data: CoverageUpdate,
+    db: Annotated[AsyncSession, Depends(get_db)],
+    current_user: Annotated[User, Depends(require_account_owner)],
+):
+    """Toggle the `can_cover_l1` flag on an engineer in your account.
+
+    Owner-only. Returns 404 if target user not in your account. Returns 422
+    if target user's role is not 'engineer' (coverage flag only applies to
+    engineers — owners/super_admins already see L1 surface; viewers/l1_techs
+    don't need this flag).
+    """
+    result = await db.execute(
+        select(User).where(
+            User.id == user_id,
+            User.account_id == current_user.account_id,
+        )
+    )
+    target = result.scalar_one_or_none()
+    if target is None:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="User not found in your account",
+        )
+    if target.account_role != "engineer":
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail="can_cover_l1 only applies to engineers",
+        )
+    target.can_cover_l1 = data.can_cover_l1
+    await db.commit()
+    await db.refresh(target)
+    return target
+
+
 @router.post("/me/transfer-ownership", response_model=AccountResponse)
 async def transfer_ownership(
     data: TransferOwnershipRequest,
diff --git a/backend/app/schemas/user.py b/backend/app/schemas/user.py
index 044e84e2..22c99928 100644
--- a/backend/app/schemas/user.py
+++ b/backend/app/schemas/user.py
@@ -60,6 +60,7 @@ class UserResponse(UserBase):
     email_verified_at: Optional[datetime] = None
     onboarding_step_completed: Optional[int] = None
     onboarding_dismissed: bool = False
+    can_cover_l1: bool = False
 
     class Config:
         from_attributes = True
@@ -73,3 +74,7 @@ class AccountRoleUpdate(BaseModel):
     # Ownership changes must go through the explicit transfer-ownership flow so
     # account.owner_id stays consistent with user.account_role.
     account_role: str = Field(..., pattern="^(admin|engineer|viewer|l1_tech)$")
+
+
+class CoverageUpdate(BaseModel):
+    can_cover_l1: bool
diff --git a/backend/tests/test_invite_seat_enforcement.py b/backend/tests/test_invite_seat_enforcement.py
index 5d002775..d0436474 100644
--- a/backend/tests/test_invite_seat_enforcement.py
+++ b/backend/tests/test_invite_seat_enforcement.py
@@ -455,3 +455,110 @@ async def test_get_seats_blocked_for_viewer(client: AsyncClient, test_db: AsyncS
 
     resp = await client.get("/api/v1/accounts/me/seats", headers=viewer_headers)
     assert resp.status_code == 403, resp.text
+
+
+# ---------------------------------------------------------------------------
+# PATCH /me/members/{user_id}/coverage — engineer L1-coverage flag
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_coverage_owner_can_toggle_engineer(client: AsyncClient, test_db: AsyncSession):
+    """Owner can set can_cover_l1=True on an engineer; response reflects new value."""
+    owner = await _register(client, email="owner_cov1@example.com")
+    account_id = uuid.UUID(owner["account_id"])
+    headers = await _login(client, email="owner_cov1@example.com")
+
+    engineer = await _add_member(test_db, account_id, role="engineer", suffix="cov1")
+
+    resp = await client.patch(
+        f"/api/v1/accounts/me/members/{engineer.id}/coverage",
+        json={"can_cover_l1": True},
+        headers=headers,
+    )
+    assert resp.status_code == 200, resp.text
+    body = resp.json()
+    assert body["can_cover_l1"] is True
+
+    # Toggle back to False
+    resp2 = await client.patch(
+        f"/api/v1/accounts/me/members/{engineer.id}/coverage",
+        json={"can_cover_l1": False},
+        headers=headers,
+    )
+    assert resp2.status_code == 200, resp2.text
+    assert resp2.json()["can_cover_l1"] is False
+
+
+@pytest.mark.asyncio
+async def test_coverage_non_owner_is_forbidden(client: AsyncClient, test_db: AsyncSession):
+    """A non-owner engineer cannot toggle coverage on themselves or others."""
+    from app.core.security import get_password_hash
+
+    owner = await _register(client, email="owner_cov2@example.com")
+    account_id = uuid.UUID(owner["account_id"])
+
+    # Create an engineer with a known password
+    eng_password = "EngPass123!"
+    engineer = User(
+        id=uuid.uuid4(),
+        email="eng_cov2@example.com",
+        name="Eng Cov2",
+        account_id=account_id,
+        account_role="engineer",
+        role="engineer",
+        is_active=True,
+        password_hash=get_password_hash(eng_password),
+    )
+    test_db.add(engineer)
+    await test_db.commit()
+
+    eng_headers = await _login(client, email="eng_cov2@example.com", password=eng_password)
+
+    resp = await client.patch(
+        f"/api/v1/accounts/me/members/{engineer.id}/coverage",
+        json={"can_cover_l1": True},
+        headers=eng_headers,
+    )
+    assert resp.status_code == 403, resp.text
+
+
+@pytest.mark.asyncio
+async def test_coverage_viewer_role_returns_422(client: AsyncClient, test_db: AsyncSession):
+    """PATCH coverage on a viewer → 422 (coverage flag only applies to engineers)."""
+    owner = await _register(client, email="owner_cov3@example.com")
+    account_id = uuid.UUID(owner["account_id"])
+    headers = await _login(client, email="owner_cov3@example.com")
+
+    viewer = await _add_member(test_db, account_id, role="viewer", suffix="cov3")
+
+    resp = await client.patch(
+        f"/api/v1/accounts/me/members/{viewer.id}/coverage",
+        json={"can_cover_l1": True},
+        headers=headers,
+    )
+    assert resp.status_code == 422, resp.text
+    assert "engineer" in resp.json()["detail"].lower()
+
+
+@pytest.mark.asyncio
+async def test_coverage_cross_account_returns_404(client: AsyncClient, test_db: AsyncSession):
+    """PATCH coverage on a user from a different account → 404 (tenancy isolation)."""
+    # Account A
+    owner_a = await _register(client, email="owner_cov_a@example.com")
+    account_a_id = uuid.UUID(owner_a["account_id"])
+    headers_a = await _login(client, email="owner_cov_a@example.com")
+
+    # Account B — a separate registration creates a new account
+    owner_b = await _register(client, email="owner_cov_b@example.com")
+    account_b_id = uuid.UUID(owner_b["account_id"])
+
+    # Add an engineer to account B
+    engineer_b = await _add_member(test_db, account_b_id, role="engineer", suffix="covb")
+
+    # Owner of account A tries to patch account B's engineer — must 404
+    resp = await client.patch(
+        f"/api/v1/accounts/me/members/{engineer_b.id}/coverage",
+        json={"can_cover_l1": True},
+        headers=headers_a,
+    )
+    assert resp.status_code == 404, resp.text