AUTONOMOUS CODING ARCHITECTURE REPORT 1. Executive Decision Implement the event-driven inventory workflow incrementally behind a compatibility boundary rather than replacing synchronous checkout behavior immediately. Preserve PostgreSQL as the system of record, introduce idempotent inventory events, validate the new path against the existing flow, and migrate warehouse synchronization before changing checkout behavior. 2. Requirement Normalization Objective Move warehouse inventory synchronization to asynchronous event processing without breaking checkout. Scope Event schema, event producer, consumer, idempotency handling, retry behavior, integration tests, observability, and controlled migration. Out of Scope Replacing PostgreSQL, redesigning the public checkout API, or rewriting the entire monolith. Success Conditions Inventory changes are processed reliably, duplicate events do not create incorrect inventory state, existing checkout clients continue to function, and rollback to the existing synchronization path remains possible. Blocking Unknowns Exact warehouse event volume and current transaction boundaries require repository inspection. Assumptions The current inventory write path can be isolated behind an application-level service. 3. Current-System Model Architecture A shared Node.js/TypeScript application handles checkout, inventory, and warehouse integrations. PostgreSQL stores authoritative inventory and order state while Redis provides supporting infrastructure. Runtime Topology Warehouse REST integration → application inventory layer → PostgreSQL. Checkout → inventory service → PostgreSQL. Data Flow Warehouse inventory updates currently enter through REST requests and synchronously update inventory records. Checkout also performs inventory mutations synchronously. Dependencies Inventory state is shared by warehouse synchronization and checkout. Critical Boundaries The inventory write transaction and checkout behavior are the highest-risk boundaries. 4. Change Impact Analysis Area Impact Confidence Evidence Inventory processing High High Current synchronization is synchronous Checkout API Medium High Must remain backward compatible Database High High PostgreSQL remains system of record Redis Medium Medium Existing infrastructure may support event coordination CI/CD Low High Existing GitHub Actions pipeline 5. Risk Register Risk Severity Evidence Mitigation Verification Rollback Duplicate events High Async processing introduces retries Idempotency key and unique event record Duplicate-event integration tests Disable consumer and use existing path Inventory race conditions High Multiple warehouses can update shared state Transactional update strategy Concurrent integration tests Revert consumer Checkout incompatibility Critical Checkout depends on inventory state Preserve existing API and compatibility layer Contract tests Restore synchronous path Event delivery failure High New asynchronous boundary Retry and dead-letter strategy Failure injection tests Disable asynchronous path 6. Atomic Implementation Plan TASK-001 — Inventory Boundary Baseline Purpose: Isolate the existing inventory mutation behavior. Dependencies: None. Scope: Existing inventory service and related tests. Implementation: Document current transaction boundaries and establish regression tests around inventory mutation. Acceptance Criteria: Existing inventory behavior is captured by tests. Checkout behavior remains unchanged. Required Tests: Unit and integration tests. Regression Scope: Component. Rollback: Revert test-only changes if necessary. Risk: Low. TASK-002 — Event Contract Purpose: Define a versioned inventory event contract. Dependencies: TASK-001. Scope: Event schema and validation. Implementation: Define event payload, identifier, version, source, timestamp, and inventory-change data. Acceptance Criteria: Events validate against the defined schema. Invalid events are rejected without mutating inventory. Required Tests: Schema and validation tests. Regression Scope: Component. Rollback: Remove unused event contract without affecting checkout. Risk: Medium. TASK-003 — Idempotent Event Consumer Purpose: Process inventory events safely. Dependencies: TASK-002. Scope: Consumer and persistence boundary. Implementation: Add idempotency tracking and transactional inventory updates. Acceptance Criteria: Replaying the same event does not duplicate inventory mutation. Failed processing can be retried safely. Required Tests: Integration and concurrency tests. Regression Scope: Service. Rollback: Disable consumer and retain existing synchronization. Risk: High. TASK-004 — Controlled Warehouse Migration Purpose: Move warehouse updates to the event path. Dependencies: TASK-003. Scope: Warehouse integration. Implementation: Publish events while preserving the existing checkout synchronization path. Acceptance Criteria: Warehouse updates reach the new consumer. Existing checkout tests remain green. Rollback can disable event consumption. Required Tests: Integration and regression tests. Regression Scope: System. Rollback: Disable event consumer and restore previous synchronization path. Risk: High. 7. Task Dependency Graph TASK-001 → TASK-002 → TASK-003 → TASK-004 8. Safety Gate Plan Pre-Flight Baseline inventory behavior, verify tests, verify rollback switch, confirm event schema. In-Flight Only modify inventory and warehouse synchronization scope. Stop on unexpected checkout changes. Post-Flight Run unit, integration, contract, concurrency, and checkout regression tests. 9. Testing and Regression Strategy The highest regression priority is checkout because it shares the inventory state boundary. Event-specific integration and concurrency tests are required before production migration. 10. Failure and Recovery Strategy If duplicate processing or inventory inconsistencies occur, disable asynchronous consumption and return to the existing synchronized path while preserving event records for diagnosis. 11. Human Escalation Points Human approval is required before changing the production inventory write path because inventory correctness is business-critical. 12. Implementation Roadmap Phase 1: Baseline and event contract. Phase 2: Consumer and idempotency. Phase 3: Controlled warehouse migration. Phase 4: Production validation and gradual expansion. 13. Readiness Assessment Architecture Confidence: 4/5 — primary boundaries are clear, but repository inspection is required. Task Atomicity: 5/5 — tasks have isolated responsibilities. Testability: 5/5 — inventory and event behavior are objectively testable. Safety: 4/5 — rollback is available through controlled consumer activation. Rollback Capability: 5/5 — existing synchronous behavior can remain available. Requirement Traceability: 5/5 — target state directly maps to the task sequence. Operational Readiness: 3/5 — production event volume and observability require confirmation. 14. Final Recommendation Adopt the event-driven design incrementally behind a compatibility boundary. Do not remove the existing synchronous checkout path until the asynchronous workflow has passed concurrency, failure, and regression validation. 15. Open Questions What is the current inventory transaction boundary? What event volume must the consumer support? Is there already a durable messaging infrastructure available?