Astra: review plan 2a (region HA spec 2, provider-neutral core)

Plan: docs/superpowers/plans/2026-10-16-region-ha-2a-core.md, 12 tasks. Spec: docs/superpowers/specs/2026-10-15-region-ha-two-box-regions-design.md, rev 15, approved, including H27. Plan 2a is the core only. 2b (joining and enrolment), 2c (infrastructure and boot) and 2d (the §8 single-box fixes) are separate plans.

The plan's code was dry-run against main 70e57449. Main has since moved; census values must be recomputed on the build base, and the plan includes tooling for that.

Judge:

1. Spec coverage for 2a's scope: - box and group roles; - the placement policy over identity-filtered candidates; - H27's refusal; - the health answer's conditions; - the address source and private-address forwarding; - the capacity metric; - §25's enforcement tests. Is anything in 2a's scope missing or wrong?
2. H27 coverage. H27 says every door that chooses a box refuses with 503 and alerts. Task 11 covers the instance create door. Do any other doors on main call the chooser? Name them.
3. Correctness of the code in each task against main: claim invariants, roster writes, concurrency.
4. Census handling: the record-write digests, and the Plan 14 overlay plan14-root-reads-region-ha-2a.tsv. Tasks 7 and 10 need platform-1e rulings. Is anything else unflagged?
5. Tests. Do they prove the claims, and would they fail without the change?

Give findings P1/P2/P3 with plan section or file:line and a failure scenario. End with a verdict: ready to build, or not.