supabase / supabase / 21593065161

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feat(telemetry): dedupe experiment exposure events by PostHog session ID (#42386)

## Summary

Adds session-based deduplication for experiment exposure events.
Previously, exposure events used `useRef` which reset on page refresh,
causing duplicate events. Now events dedupe by PostHog session ID using
`sessionStorage`, firing once per session even across page refreshes.

## Changes

- Add `captureExperimentExposure()` method to `PostHogClient` with
session-based dedupe
- Add `getSessionId()` method to retrieve PostHog session ID
- Create `useTrackExperimentExposure` hook for clean usage
- Migrate existing experiments to new hook:
  - RLS option experiment (`/new/[slug]`)
  - Realtime button experiment
  - Table create generate policies experiment

## How it works

1. Event triggered → if PostHog not ready, queue to `pendingExposures[]`
2. PostHog `loaded` → flush queue through `fireExposureIfNew()`
3. `fireExposureIfNew()` checks
`sessionStorage['ph_exposed:{experimentId}']`
4. If value matches current session ID → skip (already fired)
5. If differs or missing → fire event, store session ID

## Testing

- [x] Tested locally and on preview - verified on project creation page
- [x] PostHog events sent successfully (200 responses)
- [x] Session deduplication working (no duplicate events on page refresh
or org switch)
- [x] Lint passes with 0 errors

**Quick test:**
1. Go to `/new/<org-slug>` project creation page
2. Check `sessionStorage` for `ph_exposed:project_creation_rls_option`
key
3. Refresh page - event should not fire again (same session ID)

## Linear

Resolves GROWTH-608

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* More reliable experiment exposure reporting with session-aware
deduplication, queued delivery, and consent respect to ensure events are
recorded when available.
* **Bug Fixes**
* Prevents duplicate exposure events within a session and avoids firing
exposure... (continued)

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