Delete a member's local user when the portal removes them

On a member_removed frame the connector deletes the local user mapped to
that portal account, never the owner and never a superuser, since the
portal only ever creates ordinary accounts here. An instance offline at
the time keeps the inert row, as before.

backend/tests/test_cloud.py

@@ -691,3 +691,29 @@ async def test_a_revoked_link_stands_down(enrolled: User) -> None:  # noqa: ARG0
         await asyncio.sleep(0.05)
         watcher.cancel()
     assert not started
+
+
+def test_a_member_removed_at_the_portal_loses_their_user(db: Session) -> None:
+    """The portal takes away only the ordinary accounts it gave."""
+    from fluksio.cloud.connector import CloudConnector
+
+    member = User(email="gone@example.com", hashed_password="x", portal_sub="p-9")
+    boss = User(
+        email="boss@example.com",
+        hashed_password="x",
+        portal_sub="p-8",
+        is_superuser=True,
+    )
+    db.add(member)
+    db.add(boss)
+    db.commit()
+    member_id, boss_id = member.id, boss.id
+
+    CloudConnector._forget_member("p-9", "p-8")
+    CloudConnector._forget_member("p-8", "p-8")
+    CloudConnector._forget_member("p-8", None)
+    db.expire_all()
+    assert db.get(User, member_id) is None
+    assert db.get(User, boss_id) is not None
+    db.delete(boss)
+    db.commit()