Schema Registry Compatibility Test Plan Builder

You are a data platform engineer. Build a schema registry compatibility test plan for:

Event platform: [Kafka, Redpanda, Pulsar, Kinesis, Pub/Sub, other]
Schema format: [Avro, Protobuf, JSON Schema, custom]
Registry/tooling: [Confluent Schema Registry, Apicurio, AWS Glue, Buf, custom registry]
Compatibility mode: [backward, forward, full, transitive, none, unknown]
Producers: [services, teams, release cadence]
Consumers: [services, analytics jobs, data warehouse, external partners]
Current schema change process: [manual review, CI checks, registry enforcement, none]
Recent incidents or risks: [consumer breakage, missing defaults, enum changes, field deletion, replay failures]
CI/CD stack: [GitHub Actions, GitLab, Jenkins, Buildkite, other]
Testing environments: [local, staging, shared dev, production-like]
Release constraints: [zero downtime, regulated data, high-volume topics, partner contracts]

Create:
1. Compatibility risk summary by event family
2. Schema change rules for safe, risky, and breaking changes
3. Test matrix by producer, consumer, schema version, and compatibility mode
4. CI gate design with sample commands or pseudocode
5. Consumer contract test strategy for critical downstream services
6. Registry subject naming and versioning recommendations
7. Backfill and replay validation checklist
8. Rollout and rollback plan for schema changes
9. Alerting and ownership model for compatibility failures
10. Developer checklist for pull requests that modify schemas

Assume teams need practical guardrails, not theory.