Defense: DESIGN.md "The player contract" — Continuity requires versioned saves that survive updates. B1 spec acceptance criteria require each subsystem to round-trip; v3 only persisted a thin summary and dropped machines, allocation, per-observer suspicion, people, and sensors on load. v4 encodes the full B1 snapshot; v3/v1 still migrate. Also: serde on B1 subsystem types, spec/meta.md stage discipline, detection containment criterion fix, knowledge refresh, terminal/Bevy B1 sidebar surfacing. Co-authored-by: Cursor <cursoragent@cursor.com>