Nm Archetypes Architecture Paradigm Cqrs Es

Apply CQRS and Event Sourcing for read/write separation and audit trails

Security Scan

This is an instruction-only, architecture guidance skill about CQRS and Event Sourcing; it contains no code, does not request credentials or installs, and is coherent with its stated purpose.

Purpose & Capability

The name and description match the SKILL.md content: high-level guidance for applying CQRS and Event Sourcing. Note: the README mentions a richer 'full experience' when paired with the Claude Code plugin (agents/hooks/commands), but this packaged skill is instruction-only and contains no code or install steps—so the advertised interactive features are not present here.

Instruction Scope

Runtime instructions are purely architectural guidance, adoption steps, deliverables, risks, and troubleshooting notes. They do not instruct the agent to read files, access environment variables, call external endpoints, or execute commands beyond generic suggestions (e.g., 'ensure dependencies are installed').

Install Mechanism

There is no install spec and no code files. Nothing will be written to disk or downloaded by this skill itself.

Credentials

The skill does not request any environment variables, credentials, or config paths; there are no secrets or unrelated credentials required.

Persistence & Privilege

Flags show default invocation settings (not always:true). The skill does not request persistent presence or elevated privileges and does not modify other skills or system settings.

Assessment

This skill is safe as an informational/architectural guide: it contains no code, does not ask for secrets, and won't install anything. If you expect interactive features mentioned in the README (agents, hooks, commands), those come from a separate Claude Code plugin—only install that plugin from a trusted source. Treat the content as high-level guidance; follow your usual verification process before installing any additional tooling or sharing credentials with other plugins.

Night Market Skill — ported from claude-night-market/archetypes. For the full experience with agents, hooks, and commands, install the Claude Code plugin.

The CQRS and Event Sourcing Paradigm

When To Use

• Designing event-sourced systems with complex domain logic
• Systems requiring full audit trails of state changes

When NOT To Use

• Simple CRUD applications without complex domain logic
• Small projects where event sourcing adds unnecessary complexity

When to Employ This Paradigm

• When read and write workloads have vastly different performance characteristics or scaling requirements.
• When all business events must be captured in a durable, immutable history or audit trail.
• When a business needs to rebuild projections of data or support temporal queries (e.g., "What did the state of this entity look like yesterday?").

Adoption Steps

1. Identify Aggregates: Following Domain-Driven Design principles, specify the bounded contexts and the business invariants that each command must enforce on an aggregate.
2. Model Commands and Events: Define the schemas and validation rules for all commands and the events they produce. Document a clear strategy for versioning and schema evolution.
3. Implement the Write Side (Command Side): Command handlers are responsible for loading an aggregate's event stream, executing business logic, and atomically appending new events to the stream.
4. Build Projections to the Read Side: Create separate read models (projections) that are fed by subscriptions to the event stream. Implement back-pressure and retry policies for these subscriptions.
5. validate Full Observability: Implement detailed logging that includes event IDs, sequence numbers, and metrics for tracking the lag time of each projection.

Key Deliverables

• An Architecture Decision Record (ADR) detailing the aggregates, the chosen event store technology, the projection strategy, and the expected data consistency model (e.g., eventual consistency SLAs).
• A suite of tests for command handlers that use in-memory event streams, complemented by integration tests for the projections.
• Operational tooling for replaying events, taking state snapshots for performance, and managing schema migrations.

Risks & Mitigations

• High Operational Overhead:
  • Mitigation: Bugs related to event ordering and replays can be difficult to diagnose. Invest heavily in automation, Dead-Letter Queues (DLQs) for failed events, and regular "chaos engineering" drills to test resilience.
• Challenges of Eventual Consistency:
  • Mitigation: Users may be confused by delays between performing an action and seeing the result. Clearly document the SLAs for read model updates and manage user-facing expectations accordingly, for example, by providing immediate feedback on the command side.
• Schema Drift:
  • Mitigation: An unplanned change to an event schema can break consumers. Enforce the use of a formal schema registry and implement version gates in the CI/CD pipeline to prevent the emission of unvalidated event versions.

Troubleshooting

Common Issues

Command not found Ensure all dependencies are installed and in PATH

Permission errors Check file permissions and run with appropriate privileges

Unexpected behavior Enable verbose logging with --verbose flag