Add a DHCP pool to the gateway's dnsmasq so bridge-attached service
containers (hive-ci and future equivalents) get their addresses from
a proper DHCP server instead of a brittle static derivation.
gateway (hive-gateway.nix):
- Add IPv4 arithmetic helpers (ipToInt, intToIp, pow2) to compute the
DHCP pool range at nix eval time from bridgeIp + bridgePrefixLength.
- Reserve the last dhcpPoolSize (14) usable host addresses as the DHCP
pool (e.g. .241-.254 on a /24 with 10.42.0.0 network).
- Add dhcp-range and dhcp-leasefile to the dnsmasq settings block.
The pool is active whenever services.hyperhive.network.enable is true.
hive-ci (hive-ci.nix):
- Remove the ciBridgeIp / ciBridgeOctets static derivation and the
brittle top-of-/24 comment block.
- Switch networking.interfaces.eth0 to useDHCP = true so hive-ci gets
its address from the gateway DHCP pool.
lifecycle (mod.rs, tests.rs):
- Add DHCP_POOL_SIZE = 14 constant (must stay in sync with
dhcpPoolSize in hive-gateway.nix).
- Remap agents whose FNV-1a hash falls in the DHCP pool into the
agent-only window [2, dhcp_start - 1]. Only the rare agent whose
name hashes into the pool is affected; all others keep their IPs.
- Update and extend tests: agent range is now .2-.240 on /24;
add agent_network_ip_never_in_dhcp_pool covering 18 agent names.
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