- Add `release_channel` to Settings (Rust + TypeScript)
- Add channel selector in Settings panel (alpha/beta/stable)
- Pass `release_channel` as PostHog person property on identify
- Add `isFeatureEnabled()` helper: alpha always true, beta/stable
use PostHog flags with hardcoded fallback defaults
- Update `useFeatureFlag` to delegate to PostHog-backed evaluation
(localStorage overrides still work for dev/QA)
- Create ADR-0042 (supersedes ADR-0017)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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