Initial DDD and event sourcing review patterns

Covers:
- Aggregate design (boundaries, invariants, identity)
- Event sourcing (immutability, naming, content)
- Domain vs integration events
- Eventual consistency
- Projections and read models
- Snapshotting (when and how)
- Process managers / sagas
- Value objects
- Common anti-patterns

Focus on subtle mistakes models make, not textbook definitions.

README.md

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+# DDD & Event Sourcing Patterns
+
+Review guidance for domain-driven design and event sourcing. Focus on subtle mistakes models make and patterns they get wrong.
+
+## Contents
+
+- `DDD-CHECKLIST.md` - The review checklist covering:
+  - Aggregate Design (boundaries, invariants, identity)
+  - Event Sourcing (immutability, naming, content, reconstruction)
+  - Domain vs Integration Events
+  - Eventual Consistency
+  - Projections (read models)
+  - Snapshotting
+  - Process Managers / Sagas
+  - Value Objects
+  - Anti-Patterns to Flag
+
+## Why This Exists
+
+Models know the textbook definitions but often get the nuances wrong:
+- Making aggregates too large (data grouping vs consistency boundary)
+- Suggesting "fixes" to immutable events
+- Mixing domain and integration events
+- Expecting synchronous read model updates
+- Snapshotting prematurely
+
+This checklist catches those mistakes.
+
+## Integration
+
+```yaml
+# In your review workflow
+patterns-repo: rodin/ddd-patterns
+patterns-files: '.'
+```
+
+## License
+
+MIT