Build L epic: ACS second support spine via warm-start reselection

Build L epic: ACS as a second support spine

The national artifact's remaining structural ceiling is support richness: the 3-year ASEC x2 pool shows its edges as zero-support cells (the 5 TANF states in #368's night), thin misc/HSA carriers, and small-state credibility. ACS adds ~10x households with dense geography — the structural fix, and the machinery was built for it: #346's warm-start reselection (designed for pool changes), the #330 identity seam, the learned-prior protect-list findings (#346 comment), the coverage/parity/zero-support gate stack that just proved it digests coverage growth (#368).

Prerequisites, in order: (1) #296 ASEC vintage refresh — the same-instrument dress rehearsal for pool change under the full gate stack; (2) #380 identity spine (pool changes must mint identities correctly, not churn caches); (3) #388 register-currency preflight (so a 10x pool change surfaces every stale register in one pass, not serially). Then: ACS intake stage (harmonization to the entity/variable surface, provenance-cited), support-channel integration (clone-aware identity keys extended per #330), warm-start reselection from the enlarged pool with per-target protect-lists, full re-cert under all gates, sound-comparison vs the ASEC-only artifact (the #8/#427 protocol) + #462 promotion scorecard.

Sequencing: start after #296 + #380 land (~1-2 weeks), parallel to launch-tier paper work; the ASEC refresh itself starts now. Refs: #296, #346, #330, #380, #388, #368, #305.

Review prerequisites #296, #380, and #388 before starting the ACS intake and support-channel integration. Then trace #346's warm-start reselection, #330's identity seam, and the coverage, parity, and zero-support gates. Done means a provenance-cited ACS integration, protect-list reselection, full gate re-certification, sound comparison, and the #462 promotion scorecard.