System-design and implementation scenarios

These are specification exercises, not tutorial builds. Keep decision records and evidence; polished UI is optional.

1. Idempotent webhook receiver

Build a Laravel endpoint that authenticates a signed webhook, rejects stale/replayed requests, durably records receipt, returns quickly, processes asynchronously, deduplicates delivery and exposes operational status.

Evidence: threat model, schema constraints, retry tests, failure metrics and an explanation of acknowledged-but-not-processed state.

2. Concurrent booking

Reserve a limited resource without double booking. Implement two strategies—row locking and optimistic/constraint-based control—and compare contention, failure UX and testability.

Evidence: concurrency test, query plan and invariant definition.

3. Resumable import

Process a large file with bounded memory, per-row validation, progress, cancellation, retry and partial-failure reporting. Avoid one job per row unless measurements justify it.

Evidence: memory profile, queue design, idempotency policy and deployment behavior.

4. Modular monolith boundary

Extract a cohesive domain from a conventional Laravel application without creating a framework-avoidance layer. Define public operations/events, dependency direction and transaction ownership.

Evidence: ADR explaining what remained coupled to Laravel and why.

5. AI-assisted review workflow

Design a tool-assisted reviewer for Laravel changes. Provide a narrow prompt, repository rules, security boundary, representative eval cases and metrics comparing unaided review with the workflow.

Evidence: false-positive/negative analysis, prompt-injection test and human approval boundary.