Phase 4 exited 2026-05-16. All three planned lanes shipped:
sample_efficiency (one-shot-per-correction, replay 1.0),
long_context_cost (slope 0.99 linear after ADR-0019 Stage 1),
multi_agent_composition (15/15 public, composition does not
launder identity violations).
PROGRESS.md updated with full Phase 4 narrative and exit
checklist.
ADR-0020 opens the next sequencing decision: Phase 5
(curriculum era) vs. Rust backend parity port. Three options
laid out (A: Phase 5 first, B: Rust first, C: parallel with
per-surface bit-identity gating). Recommendation: Option C.
Status remains Proposed pending user confirmation.
