# Validation Guide
Validation should be phase-based and deterministic.
The validation phases must follow `SPEC.md`:
1. Document Validation
2. Canonical Object Model Validation
3. Structural Validation
4. Type Validation
5. Reference Validation
6. Semantic Validation
7. Extension Validation
Validation should return a `ValidationReport`, not panic.
Semantic and extension phases resolve `dtcs:` identifiers through the
embedded registry (`registry::default_registry`). Callers may inject a
vendor catalog with `validate_with_registry`. Unsupported mandatory
extensions produce `dtcs:unsupported-extension`.
Invalid contracts should produce diagnostics with:
- id
- severity
- category
- stage
- message
- location/object reference
- optional remediation