NC Phase 1: close the cheap loop — Tier 0/1 verifier-gated auto-apply + rollback

[mercurialsolo]

Part of #358. Design: docs/niche-construction.md §Acceptance.

Phase 1 — Close the cheap loop (Tier 0/1, verifier-gated + rollback)

First closing of reciprocal causation, on the reversible/bounded surfaces only.

Scope

• Tier 0 (surface A): per-session policy (session_policy.rs) — full auto, ephemeral, auto-expires.
• Tier 1 (surfaces B, C): brain prompts/few-shot weighting (prompts.rs, decisions.rs) and routing/auto-rules (rules.rs) — auto-apply only when a verifier (verify.rs) confirms improvement on a guarded metric AND worsens none.

Deliverables

• Auto-apply path: needs-model item → propose niche edit → verifier gate → apply with provenance.
• Rollback ledger (coord): every auto-applied edit records need, verifier verdict, fitness baseline.
• Counteractive rollback: regression on any guarded metric over N tasks → auto-revert + quarantine (not re-proposed without new evidence).
• Feature-flag + charter max_tier gating so it is opt-in.

Acceptance

• No Tier-1 edit takes effect without a passing verifier + armed rollback.
• Surfaces F/G are never touched (no editing verifiers/guarded metrics; no editing charter/harness).
• Demonstrated revert on an injected regression.