feat: add client identity tracking and PostHog userId mapping

[HugoRCD]

This pull request introduces a user identity context to the client logging system, allowing you to associate logs with user information (such as userId and orgId) across the client, server, and external drains like PostHog. It also updates documentation, playground tests, and the PostHog adapter to support and demonstrate this new identity feature. The changes ensure that identity fields are automatically included in all client logs, can be overridden per event, and are correctly mapped to analytics drains.

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Project	Deployment	Actions	Updated (UTC)
evlog-docs	Ready	Preview, Comment, Open in v0	Feb 14, 2026 4:11pm

[github-actions]

Thank you for following the naming conventions! 🙏

[pkg-pr-new]

npm i https://pkg.pr.new/evlog@78

commit: 0cde4b1

[Copilot]

Pull request overview

This pull request introduces a comprehensive user identity tracking system for the evlog client logging framework, enabling automatic association of logs with user information across the entire stack.

Changes:

• Added setIdentity() and clearIdentity() functions for client-side identity context management
• Updated PostHog adapter to automatically map event.userId to PostHog's distinct_id field with a proper fallback chain
• Added comprehensive test coverage for identity tracking and PostHog userId mapping
• Enhanced documentation with identity usage examples and PostHog integration details
• Added interactive playground demos for identity feature testing

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/evlog/src/runtime/client/log.ts	Core implementation of identity context with setIdentity() and clearIdentity() functions, spreads identity fields into all emitted logs
packages/evlog/src/adapters/posthog.ts	Updated distinct_id mapping to use fallback chain: config.distinctId → event.userId (if string) → event.service
packages/evlog/src/nuxt/module.ts	Added auto-imports for setIdentity and clearIdentity functions
packages/evlog/test/identity.test.ts	Comprehensive test suite covering identity setting, clearing, overrides, tagged logs, multiple fields, and replacement behavior
packages/evlog/test/adapters/posthog.test.ts	Added tests for userId-to-distinct_id mapping, priority handling, and non-string userId fallback
apps/playground/app/pages/index.vue	Added interactive handlers for testing identity set, log, override, and clear operations
apps/playground/app/config/tests.config.ts	Added Identity test section with four interactive test cases demonstrating identity features
apps/docs/content/3.adapters/4.posthog.md	Updated PostHog documentation to explain distinct_id fallback chain and automatic userId mapping
apps/docs/content/1.getting-started/2.installation.md	Added Client Identity section with usage examples and auth middleware integration pattern

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