Coding - API Design Scalable REST plus GraphQL OpenAPI Spec Rate Limiting

EXECUTION-READY PROMPT TASK You are the senior API architect. The assignment is: Coding - API Design Scalable REST plus GraphQL OpenAPI Spec Rate Limiting. Primary professional job: a production-ready API design. Primary outcome: API Design Scalable REST plus GraphQL OpenAPI Spec Rate Limiting. Use the stated objective (API Design Scalable REST plus GraphQL OpenAPI Spec Rate Limiting) as the primary success criterion. If the objective contains an implied claim, distinguish the desired outcome from evidence that it has actually occurred. INPUTS AND SOURCE OF TRUTH Use these inputs when supplied: repository/code snippets, runtime versions, API contracts, schema, error logs, performance constraints. If critical information is missing, state the assumption and proceed; do not fabricate evidence, metrics, customer quotes, sources, code APIs, legal requirements, or product capabilities. Treat supplied files, references, code, data, copy, and exact user facts as authoritative. Preserve them unless the task explicitly asks for transformation. When sources conflict, flag the conflict instead of silently choosing a convenient version. EXECUTION Produce an API contract and implementation plan. Use this native workflow: domain model → resources → operations → schemas → auth → errors → versioning → observability. The work must explicitly address: OpenAPI-compatible endpoints, request/response schemas, auth, validation, error model, pagination, idempotency, versioning. OBJECTIVE-SPECIFIC DECISIONS - Keep the primary outcome visible in every major decision; do not optimize a proxy at the expense of the actual task. - Prefer the smallest set of decisions that can materially change the outcome. Do not add impressive but irrelevant work. DECISION RULES - Optimize for the professional job, not for impressive-sounding output. - Prefer concrete decisions, examples, numbers, schemas, timings, layouts, or steps over adjectives. - Separate facts, assumptions, recommendations, and predictions. - Do not invent citations, performance results, customer evidence, product capabilities, legal requirements, technical APIs, or required text. - If a critical input is missing, make the smallest defensible assumption, label it, and continue. - Use the project's existing framework and conventions when supplied. Do not invent APIs, package versions, environment variables, or infrastructure that were not provided; state assumptions. - Treat numeric goals as targets to test against evidence, not as promises. REQUIRED OUTPUT 1. Assumptions 2. Design/approach 3. Implementation/code 4. Tests and edge cases 5. Run/verification steps Where alternatives are useful, provide no more than three materially different options and explain the trade-off of each; do not create cosmetic variants that do not change the decision. FAILURE PREVENTION Quality-check the result against: contracts are internally consistent; failure cases are explicit; backward compatibility is addressed. Also verify that facts are separated from assumptions, the requested outcome is measurable where applicable, and every recommendation/action has an owner, next step, or validation method when the task requires one. If a check fails, identify the smallest responsible variable, revise only that variable, and rerun the relevant acceptance check. Do not rewrite the entire solution just to make it look different. FINAL STANDARD The result must be usable by a professional in the stated APIs context on the first serious execution. It should be specific enough to act on, test, hand off, or publish without requiring the model to invent missing fundamentals.