D-111: align VR1 v6 subcarve to deployed NN mnemonic; fix ULA-gen doc bug ...

Basing VR1 NetBox on the real netbox.baldurkeep.com modeling (operator
directive). A read-only live export confirmed VR0-DC0/Willamette use an NN
net-byte mnemonic with /60-per-plane + /64-active; dc-dc-prefixes-import.py
did not match it (arbitrary contiguous indices, /64-only).

DOCFIX-182 / D-111: carve_v6 replaces carve_ula/carve_gua -- provider :10
(+API-VIP :11) GUA, metal /60 shared by admin :20 / internal :21, data :30,
storage :40, repl :50, all /60+/64 ULA; the ULA /56 is indexed to the GUA site
nibble so the 4th hextet reads DC.NN in both families. Direct-math _sub_at (no
subnet enumeration -- preserves the DOCFIX-181 no-hang property). Harness
40 -> 53 PASS. D-111 ADOPTED in design-decisions.md; scope-doc sub-decision #1
ratified.

DOCFIX-183: fix the invalid-IPv6 ULA-generation sed in the netem/ULA proposal
doc (4+6 -> 2+4+4 hextets, caught by actually running it); ratified VR1 ULA is
fd50:840e:74e2::/48.

repo-lint 0 fail; tests/dc-dc-prefixes-import 53/53.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

DOCFIX-181: fix carve_gua subnet-enumeration hang (gauntlet was stalling) ...

netbox/dc-dc-prefixes-import.py::carve_gua() list()-ed every /64 subnet of the
GUA prefix (2**24 = ~16.7M for D-101's /40 example) only to use the first ->
hung/OOM. Real import runs would hang identically, not just the test. Fixed to
take the first /64 lazily via next() (O(1)).

Added a faulthandler watchdog to tests/dc-dc-prefixes-import/test_logic.py so a
future blocking regression self-aborts with a traceback after 30s instead of
silently stalling the whole run-tests-all.sh gauntlet -- the false-green that
let the ledger claim "40/40" for a test that never actually completed.

tests/dc-dc-prefixes-import: 40/40 in 0.05s (was: hung indefinitely).
Full gauntlet: ALL GREEN (52 harnesses). repo-lint 0 fail.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

DOCFIX-160: adversarial review pass finds and fixes 3 real issues ...

Ran a fresh-eyes review subagent across tonight's full deliverable set
(lib-net.sh/lib-hosts.sh selectors, the NetBox DC-DC pipeline, all seven
Stage 1-7 runbooks). Found and fixed:

- A real Python control-flow bug in tests/dc-dc-prefixes-import/
  test_logic.py: a `return` inside `try` made the `else` clause
  unreachable, silently leaving 3 happy-path assertions uncounted.
  37/37 -> 40/40 after the fix (independently reproduced before trusting
  the finding).
- A self-contradictory pair of comments in dc-dc-prefixes-import.py about
  /19-vs-/22 subnet arithmetic (no functional bug, wrong prose).
- Stale self-referential text in the Stage 4 runbook, written before
  Stage 3 existed and never reconciled once it did.

Corrected the 40/40 count in the workflow tracker and session ledger.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A

DOCFIX-152: NetBox multi-DC/dual-stack import pipeline (gap #3 mechanism) ...

Adds netbox/dc-dc-prefixes-import.py, extending the v1 single-site IPv4-only
NetBox import to VR1's two-DC dual-stack model (D-101). DC1's v4 planes are
hardcoded (D-101: inherited from DC0 unchanged, this is decision text, not
an inference); DC2's v4 supernet, the org ULA /48, and the per-DC GUA carve
are all required env vars with no defaults, failing loud rather than
inventing any of them. 37/37 tests against a fake in-memory NetBox client
(no live NetBox reachable this session). Closes the tooling half of gap #3;
the real literals still need operator/NetBox assignment.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A