Routes are matched as written, so such a prefix never equals the one a
client announces. The approval APIs answer 400 and autoApprovers refuses
it at load and write, with Tailscale's text.
One peer build per tag/user/IP/route write; callers detect policy moves
via NodesGeneration. Per-node caches only store results for the node
pm holds, so a mapper reading mid-build cannot pin a stale filter.