Dependency resolution

When you ask to run an operation, the engine resolves the dependency chain by combining:

1. Implicit edges — any {{X.y}} reference in a path/body/header implies a dep on whichever operation produces X.y
2. Explicit edges — depends_on: declarations for prerequisites that don’t produce values
3. Topological sort with deterministic lexicographic tie-break

See Mental model for the algorithmic overview and Engine requirement §3.1 for the full spec.