# Sprint 220 Plan: Security Propagation Contract Gate

## Goal
Require explicit deny-by-default security propagation constraints.

## Steps
- Step 2139: Enforce `security.deny_by_default=true` contract.
- Step 2140: Emit security contract invalid diagnostics.
- Step 2141: Add security category closure metrics in summary outputs.
- Step 2142: Include security contract packet in benchmark rows.
- Step 2143: Add `Sprint220IntegrationSummary.h`.