feat: Adds data domain - product-analytics knowledge

domains/data/knowledge/metrametrics-identity.md

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+---
+name: metrametrics-identity
+domain: data
+description: isOptIn:true unconditionally strips user identity in MetaMetricsController — always sends as anonymous ID
+---
+
+# MetaMetrics Identity Stripping
+
+## The Mechanism
+
+In `MetaMetricsController` (`app/scripts/controllers/metametrics-controller.ts`):
+
+```typescript
+if (excludeMetaMetricsId || (isOptIn && !metaMetricsIdOverride)) {
+  idType = 'anonymousId';
+  idValue = METAMETRICS_ANONYMOUS_ID; // 0x0000000000000000
+}
+```
+
+When `isOptIn: true` with no `metaMetricsIdOverride`:
+- The user's real `metaMetricsId` is discarded
+- ALL such events share a single anonymous ID (`0x0000000000000000`) in Segment
+- User-level attribution is completely lost
+
+This is **unconditional** — it applies to fully opted-in users with valid IDs, not just anonymous users.
+
+## Intended Use
+
+The onboarding opt-in flow (`creation-successful.tsx`) — where the user hasn't committed to MetaMetrics yet and no `metaMetricsId` has been persisted. The event must fire regardless of opt-in state.
+
+## The Misuse Pattern
+
+Post-opt-in `trackEvent` calls with `{ isOptIn: true }` without `metaMetricsIdOverride`. Defeats the purpose of Segment user-level dimensions (account types, feature flags).
+
+## Detection
+
+```bash
+grep -r "isOptIn: true" app/scripts/ ui/ --include="*.ts" --include="*.tsx"
+```
+
+Any occurrence outside `creation-successful.tsx` (or the onboarding flow) is suspect.

domains/data/knowledge/segment-governance.md

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+---
+name: segment-governance
+domain: data
+description: Segment event governance via segment-schema is advisory — no CI enforcement prevents unregistered events from shipping
+---
+
+# Segment Event Governance
+
+## Architecture
+
+| Component | Location |
+|-----------|----------|
+| Tracking plan | `Consensys/segment-schema` → `tracking-plans/metamask-extension.yaml` |
+| Event registry | `shared/constants/metametrics.ts` → `MetaMetricsEventName` enum (300+ entries) |
+| Review process | `CONTRIBUTING.md` in segment-schema; Data Council review |
+| Governance channel | `#metamask-metametrics`, `@consensys/data-council` |
+
+## The Gap
+
+There is **no CI enforcement** in the extension repo. A developer can:
+
+1. Add entry to `MetaMetricsEventName` enum
+2. Call `trackEvent` with it
+3. Merge and ship to production
+
+...without registering in segment-schema or going through Data Council review.
+
+## Implications
+
+- Schema drift between tracking plan and production events
+- No property schema validation for unregistered events
+- Billing impact goes unreviewed
+- Data Council review is bypassable by omission
+
+## Recommended Fix
+
+CI check that:
+1. Parses `MetaMetricsEventName` entries
+2. Validates each against `tracking-plans/metamask-extension.yaml`
+3. Fails build if event is missing from the plan