[rmkr-dev]

Adds a Skillbook entry and a matching Promptbook entry for making retried POST/PATCH requests safe in Spring Boot APIs.

Skill: api-idempotency-key-guardrails

• Per-endpoint contract: required vs optional, key scope, retention, store-down behaviour
• Key validation and scoping to client + method + route template, request fingerprint with 422 on reuse
• Atomic claim with 409 for in-flight duplicates, record committed with the business write, leases on in-progress rows
• Which outcomes get stored vs released, faithful replay, retention cleanup, stored bodies treated as sensitive
• Filter order, metrics, OpenAPI docs; Flyway table, claim SQL, problem response, checklist, anti-patterns, SKILL.md stub

Prompt: add-idempotency-keys

• Contract table first, then migration, filter/interceptor, outbound key propagation, OpenAPI and client retry changes
• Tests for replay, mismatch, concurrent duplicates, crash mid-request and expiry; ships optional before required

Catalogs go to 49 skills / 49 prompts. node scripts/site-check.mjs passes locally.