Files
multica/server
Eve 1fee14bd2c feat(featureflag): framework-level feature flag system (MUL-3615)
Introduces a reusable feature flag framework so future features can adopt
flags without writing infrastructure code.

Backend: server/pkg/featureflag (Go)
- Service / Provider / Decision separation per Martin Fowler's Toggle
  Point / Toggle Router / Toggle Configuration pattern.
- Providers: StaticProvider (rules in source control), EnvProvider
  (FF_<KEY> overrides for ops kill switches), ChainProvider
  (first-hit-wins composition).
- EvalContext carried through context.Context with WithEvalContext /
  EvalContextFrom; supports user_id, workspace_id, free-form attributes.
- PercentRollout via deterministic FNV-1a bucketing; same user always
  lands in the same bucket so experiments do not flap between requests.
- Nil-safe Service: a nil *Service or missing flag returns the caller's
  default so business code never panics on a missing flag.
- 100% unit-test coverage with -race; go vet clean.

Frontend: packages/core/feature-flags (TypeScript)
- Same vocabulary as the Go side (Decision, EvalContext, Rule,
  PercentRollout). FNV-1a parity ensures cross-tier bucket agreement.
- FeatureFlagService + StaticProvider + ChainProvider in pure TS.
- React glue: FeatureFlagsProvider, useFlag(key, default),
  useVariant(key, default). Hooks fall back to the default when no
  provider is mounted so Storybook / unit tests stay simple.
- Vitest tests for service, providers, hash, and React hooks.

Docs: docs/feature-flags.md — wiring, EvalContext, toggle points,
backend-protection note, and the standard best-practice checklist.

The framework intentionally has no third-party Go deps and no API
surface beyond what real callers will need. New providers (DB, remote
config, LaunchDarkly) plug in by implementing Provider; no existing
caller has to change.

Co-authored-by: multica-agent <github@multica.ai>
2026-06-24 13:11:39 +08:00
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