feat(nest-profiler-event-emitter): profile @nestjs/event-emitter domain events

[fpasquet]

Summary

Adds @eleven-labs/nest-profiler-event-emitter, the 14th publishable collector, closing the last blind spot around first-party NestJS integrations: domain events dispatched through @nestjs/event-emitter. Today a controller answers, the request profile closes, and whatever the @OnEvent listeners did is never recorded anywhere.

The collector contributes three surfaces:

1. An Events panel on the emitting profile — one row per emit / emitAsync call with the event name, listener count (0 · no listener flagged in amber), duration, async flag and redacted payload. Entries feed the performance-rule engine under their own event tag domain, so slow / n-plus-one / chatty thresholds never inherit the query ones.
2. An event entrypoint — each @OnEvent execution becomes a first-class profile carrying its own logs, queries and sub-requests, in a dedicated Events list view with Status / Event filters and an Event detail tab. Same philosophy as nest-profiler-commander for CLI commands; opt out with profileListeners: false.
3. An Event Listeners group in the Routes panel, scanning providers and controllers.

The implementation started from a collector prototyped outside the repo. Porting it to the monorepo conventions (CommonJS + repo-build, @repo/* presets, ConfigurableModuleBuilder + buildCollectorModule, Jest at the 90 % gate) surfaced several defects, fixed here:

• @OnEvent on controllers was ignored — the scan only walked getProviders(), while @nestjs/event-emitter's own loader also scans controllers. Those listeners were missing from both the Routes panel and the profiling wrapper.
• A misleading "process-local storage" warning was copied from the commander collector. Event listeners run in the same process as the profiler UI, so in-memory storage works fine — the warning fired on the default configuration.
• Nothing was restored on shutdown — neither the patched emit/emitAsync nor the wrapped handlers, leaking across apps in e2e suites that create and destroy several.
• priority: 25 collided with the validator collector.
• A /g RegExp in ignoreEvents matched every other event (RegExp.test advances lastIndex).
• An emitterToken resolving to a non-emitter crashed bootstrap — found while writing the tests; now guarded structurally.

Two deliberate additions on top: configurable error classification (error?: ProfilerErrorOptions, with the status layer off by default so an exceptions override is actually meaningful — the GraphQL kind does the same) and TaggableCollector support.

Two limitations are documented rather than solved: request-scoped subscribers cannot be profiled (@nestjs/event-emitter resolves a fresh instance per event, so there is no stable handler to wrap), and EventEntry.error is rarely populated (@OnEvent defaults to suppressErrors: true; the handler's own event profile records the failure either way).

Demonstration in example-api

The notifications context gains a third EventPublisher adapter, backed by EventEmitter2. Since it needs no infrastructure, it becomes the default in place of the no-op adapter, and POST /api/v1/products now publishes product.created — so the collector has data out of the box, with no Docker.

NotificationsNoopModule is kept as the minimal reference implementation of the port but is no longer wired; its docblocks say so explicitly.

Verified

Beyond CI: the full e2e suite (11 suites, 71 tests, including 6 new ones), plus a manual run against the example app confirming the Events panel (1 listener, 25 ms, redacted payload), the ?view=event list, the Event Listeners Routes group, a clean boot with PROFILER_ENABLED=false, and the absence of the spurious storage warning under in-memory storage.

Screenshots are declared in scripts/generate-profiler-screenshots.ts (events.png, events-list.png) but not generated in this PR — nothing references them yet, so there are no broken links.

Related issue

Closes #228

Checklist

• Tests were added or updated to cover the change
• Documentation was added or updated
• A changeset was added, or this PR does not affect published packages
• Breaking changes use a major changeset with a BREAKING: note

Breaking changes

• This PR includes breaking changes

New package only — nothing existing changes shape. The one consumer-visible shift is confined to example-api, where the default EventPublisher adapter moves from the no-op to the in-process emitter.

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Project	Deployment	Actions	Updated (UTC)
nest-profiler	Ready	Preview, Comment	Jul 26, 2026 9:04am
nest-profiler-example	Ready	Preview, Comment	Jul 26, 2026 9:04am