A 30-LAN generate request already fits in 172.20.0.0/16, but trees
with depth/branching that multiply past 256 (e.g. depth=6,
branching=4 ≈ 5k LANs) hit AllocatorExhausted before the first
write.
SubnetAllocator now accepts a full CIDR base ("172.16.0.0/12" →
4096 /24s) in addition to the legacy two-octet shorthand ("172.20",
auto-lifted to /16). The parent must be ≤/24; a /24 base yields
exactly one slot. Iteration order is preserved for /16 bases so
existing topologies keep their third-octet sweep; /12 adds a
second-octet dimension underneath.
Defaults bumped to 172.16.0.0/12: TopologyConfig.subnet_base_prefix,
/next-subnet query param, and the mutator's add-LAN fallback. The
field pattern widens to accept CIDR. create-blank and manual LAN
CRUD still use "10.0" (lifts to /16) — one DMZ LAN per topology,
256 is plenty.
MazeNET phase 2 step 1. Pulls inline IP/subnet allocation out of the
generator into decnet/topology/allocator.py so the editor + reconciler
can reuse the same primitives without duplicating logic.
- IPAllocator: stateful host-IP handout with reserve/release/is_free.
- SubnetAllocator: /24 handout under a base prefix, skips reservations.
- reserved_subnets(repo): collects claimed subnets across every
non-torn_down topology so concurrent drafts cannot collide.
- generate() accepts reserved_subnets= to skip existing claims.
Generator output is byte-identical under seed (behavior preserved).
