feat: add drain log hook

[HugoRCD]

This pull request introduces a new "drain" hook (evlog:drain) to the logging system, enabling easy integration with external log aggregation services (such as Axiom or Loki).
The hook is called after a log event is emitted and provides the complete event and relevant request metadata. The changes include updates to the logger internals, type definitions, plugin implementation, and documentation, along with an example plugin for usage reference.

[vercel]

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Project	Deployment	Review	Updated (UTC)
evlog-docs	Ready	Preview, Comment	Jan 28, 2026 9:53am

[github-actions]

Thank you for following the naming conventions! 🙏

[Copilot]

Pull request overview

This pull request adds a new "drain" hook feature to the evlog logging library, enabling users to send logs to external services like Axiom, Loki, or custom endpoints. The feature is designed as a fire-and-forget mechanism that never blocks HTTP responses.

Changes:

• Added evlog:drain hook that receives a DrainContext containing the complete WideEvent and optional request metadata
• Modified RequestLogger.emit() to return WideEvent | null instead of void, enabling the drain hook to access the emitted event
• Updated internal emitWideEvent() function to return the formatted event or null when sampled out

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/evlog/src/types.ts	Added DrainContext interface and evlog:drain hook declaration; updated RequestLogger.emit return type
packages/evlog/src/logger.ts	Modified emitWideEvent and RequestLogger.emit to return WideEvent | null
packages/evlog/src/nitro/plugin.ts	Integrated drain hook calls in error and afterResponse handlers with error handling
packages/evlog/src/index.ts	Exported new DrainContext type
apps/playground/server/plugins/evlog-drain.ts	Added example implementation of the drain hook
apps/docs/content/1.getting-started/2.installation.md	Documented the new drain hook feature with examples
AGENTS.md	Added drain hook documentation for AI agents

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