substep-explicit-defer

# Substep Explicit DEFER

Substeps under aggregation default to DEFER. These two forms are equivalent:
- Bare substep (no transitions) — implicit DEFER
- Explicit `- PASS DEFER` / `- FAIL DEFER`

## 1. Validate

- PASS ALL COMPLETE
- FAIL ANY STOP

### 1.1 First check

- PASS DEFER
- FAIL DEFER

```bash
rd echo "first"
```

### 1.2 Second check (implicit DEFER — equivalent)

```bash
rd echo "second"
```