Pipeline execution model

┌─ global before ──┐   ┌── @UsePipeline ──┐   ┌─ global after ──┐
│ LoggingBehavior  │ → │ AuditBehavior    │ → │ TraceBehavior   │ → handler.execute()
│ ZodValidation    │   │                  │   │ MetricsBehavior │
└──────────────────┘   └──────────────────┘   └─────────────────┘
                    ← response propagates back through the chain ←

1. At startup the pipeline finds the CQRS handlers through Nest’s DiscoveryService, by the metadata their @CommandHandler, @QueryHandler and @EventsHandler decorators record.
2. For each matching handler it precomputes request-independent metadata and resolves singleton behavior instances. Behaviors that cannot be resolved as singletons are marked for per-invocation resolution.
3. Per invocation: creates a PipelineContext, resolves any dynamic/request-scoped/transient behaviors with the applicable Nest context ID, takes the tenant and correlation id from the configured sources, and runs the chain inside them (and AsyncLocalStorage) so nested dispatches inherit them.
4. The common all-singleton path reuses the pre-resolved instances with no request-time reflection or behavior DI lookup; scoped/dynamic behaviors intentionally use request-time DI resolution.
5. Requires Nest and Nest CQRS 12. Request-scoped and transient handlers (Scope.REQUEST, Scope.TRANSIENT) rely on AsyncContext, which earlier CQRS versions do not provide.

Execution Order

Phase	Source	Position
Global before	globalBehaviors.before	Outermost (first to run)
Handler-level	@UsePipeline(...)	Middle
Global after	globalBehaviors.after	Innermost (closest to handler)
Handler	execute() / handle()	Core

Deduplication

When both global and handler-level configurations include the same behavior class, the handler’s complete options record wins while the behavior retains its global chain position. Global duplicates are deduplicated automatically.

// Global config
PipelineModule.forRoot({
  globalBehaviors: {
    scope: 'all',
    before: [LoggingBehavior], // default options: metricLogLevel='log', requestResponseLogLevel='debug'
  },
})

// Handler overrides LoggingBehavior's options
@CommandHandler(CreateUserCommand)
@UsePipeline(
  [LoggingBehavior, { requestResponseLogLevel: 'log' }], // ← wins over the global entry
)
export class CreateUserHandler { /* ... */ }

// Effective chain for CreateUserHandler:
//   [LoggingBehavior at global-before position, using handler opts] → handler

Configure mandatory authentication/authorization behaviors in global before. Core preserves that outer position even when a handler redeclares the behavior to provide rules or other options, preventing inner cache/idempotency hits from bypassing the guard.