Lamina idempotency concurrency

Skill aryaniyaps/lamina/skills/lamina-idempotency-concurrency

Headless Product Design skill for AI coding agents | Design how it works, verify what you ship.

Install

npx -y skills add aryaniyaps/lamina --skill lamina-idempotency-concurrency

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Duplicate actions and simultaneous edits — double-submit, concurrent admin updates, and safe retries in product behavior. Use when shared resources can be mutated by multiple actors or requests.

SKILL.md

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Idempotency and Concurrency

Design product behavior so duplicate actions and simultaneous edits cannot break invariants — without prescribing database locks or frameworks.

Decision frameworks

Idempotent operation: Repeating the action has the same effect as once (click "generate ticket" twice → still one ticket).
- When to use: Any create or payment action.
- How: Disable button after submit; show existing result on repeat; scenarios for double-click.
Concurrent edit conflict: Two actors change the same resource (two admins assign different venues).
- When to use: Shared admin resources, collaborative editing.
- How: Last-write-wins with audit, optimistic conflict UI, or lock-while-editing — document product choice in scenarios.
Fencing: Stale action cannot apply after state changed (regenerate ticket on exam already completed → blocked with clear reason).

Checklists

List mutating operations; mark which must be idempotent.
For shared editable resources, define conflict behavior.
Design UX for in-flight requests (disabled submit, progress).
Write scenarios: concurrent_edit, duplicate submit, stale action.
Verify phase: attempt duplicate and concurrent paths on live product.

Anti-patterns

Double ticket on double-click: No idempotency on create.
Silent overwrite: Admin B's venue change lost without notice.
Optimistic UI without rollback: Show success then revert confusingly.

Examples

Two admins, one exam: Admin A assigns Hall 1; Admin B assigns Hall 2 simultaneously. Product rule — second save warns "venue changed since you opened; review and confirm" with diff, not silent overwrite.