feat(l1): PATCH /accounts/me/members/{id}/coverage for engineer L1-coverage flag

Owner-only endpoint to toggle can_cover_l1 on an engineer user. 422 if target
role is not engineer (owners/super_admins already see L1 surface; viewers/
l1_techs don't need this flag). 404 for cross-account targets.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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