dc-region-topology.sh: the plane-topology builder the repo never had ...

A read-only survey found THREE dc0 carve components with no repo tool at
all -- the named plane fabrics, the six v4 plane subnets, and the site
placement tag were created ad-hoc in the Stage-4 window, with the mutations
landing only in ~/as-executed/2026-07-23-stage4-carve.log, which is not in
the repo. When D-132 q1 required rebuilding that carve on a new region
there was nothing to re-run. This closes the gap so dc1 and every Roosevelt
DC standup rebuild from a tool rather than a transcript.

check/apply over: five named plane fabrics, six spaces, six v4 plane
subnets on the right VLANs with the ruled gateways, VLAN->space bindings,
and the openstack-<site> tag. Expected values derive from lib-net.sh;
fabric names derive from the site token. Numeric MAAS ids are resolved
per-run by name or CIDR and never persisted -- the pre-migration capture's
id= values are database row ids, not 802.1Q tags, and nothing reads them.

metal-admin deliberately keeps MAAS's own auto-created fabric: it is a
discovery artifact created when the rack registers, Juju binds spaces
rather than fabrics, and renaming it would fight MAAS for ownership of its
own object for no functional gain. The check asserts only that it does not
share a fabric with a named plane.

Every mutating path is gated by maas-profile-assert.sh first -- against
the wrong profile this apply is an idempotent no-op that prints PASS.
--profile has NO default, because the repo-wide default 'admin' resolves
to the Office1 region.

Harness 35/35; 4 mutations each killed tests (region gate removed, profile
defaulted to admin, space-binding assertion, fabric-placement assertion).
Fixtures corrected against a live read: MAAS reports an unbound VLAN as
the string "undefined", not null, so the first fixtures graded a payload
MAAS never emits.

Live read-only check against the new dc0 region: 5 passed, 22 failed,
exit 1 -- the expected shape of a region that has only auto-discovered its
own two NICs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HvCyrwvYTTcDYnRErfMsNf