feat: add feature-flags skill with MetaMask Mobile overlay

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add `feature-flags` skill with a repo-agnostic base and a MetaMask Mobile overlay for version-gated remote flags. Marked `base: true` so it installs even when its domain is filtered out. ([#147](https://github.com/MetaMask/skills/pull/147))
 - Add `analytics` skill (`platform/analytics`, moved from `coding`) with a repo-agnostic base and a MetaMask Mobile overlay for the canonical tracking API. Marked `base: true` so it installs even when its domain is filtered out. ([#140](https://github.com/MetaMask/skills/pull/140))
 
 ## [0.3.1]

domains/platform/skills/feature-flags/repos/metamask-mobile.md

@@ -0,0 +1,71 @@
+---
+repo: metamask-mobile
+parent: feature-flags
+---
+
+# Feature flags — MetaMask Mobile
+
+Human-facing file map: `docs/readme/version-gated-feature-flags.md`.
+
+## Canonical API
+
+| Role | Path |
+|------|------|
+| Helper | `app/util/remoteFeatureFlag/index.ts` → `validatedVersionGatedFeatureFlag`, `hasMinimumRequiredVersion` |
+| Raw flags | `RemoteFeatureFlagController.remoteFeatureFlags` (no client version gating) |
+| Selectors | `app/selectors/featureFlagController/` or `**/selectors/featureFlags/` |
+| Names (when the flag is overrideable in dev tools) | `app/constants/featureFlags.ts` → `FeatureFlagNames` |
+
+`validatedVersionGatedFeatureFlag` compares against the native binary version from `react-native-device-info` `getVersion()`, not `package.json`. Progressive-rollout wrappers `{ name, value: { enabled, minimumVersion } }` are unwrapped in the helper.
+
+`hasMinimumRequiredVersion` is the lower-level compare used inside the helper. Import it from the util only for a standalone version check.
+
+Multi-version flags shaped `{ versions: { "7.53.0": value } }` are resolved at fetch time by the controller. Consumers read the processed value — no helper call for that shape.
+
+## Requirements
+
+- Selectors call `validatedVersionGatedFeatureFlag`. UI and hooks only `useSelector(selectXEnabled)`.
+- Non-standard flag shapes (e.g. `active` instead of `enabled`) map to `{ enabled, minimumVersion }` before the helper.
+- Remote flag wins when valid. Use `?? env/local` when the helper returns `undefined` (invalid shape, or `OVERRIDE_REMOTE_FEATURE_FLAGS=true`).
+
+```ts
+import { createSelector } from 'reselect';
+import { selectRemoteFeatureFlags } from '../index';
+import {
+  validatedVersionGatedFeatureFlag,
+  type VersionGatedFeatureFlag,
+} from '../../../util/remoteFeatureFlag';
+
+export const selectMyFeatureEnabled = createSelector(
+  selectRemoteFeatureFlags,
+  (remoteFeatureFlags) => {
+    const localFlag = process.env.MM_MY_FEATURE_ENABLED === 'true';
+    const remoteFlag =
+      remoteFeatureFlags?.myFeature as unknown as VersionGatedFeatureFlag;
+
+    return validatedVersionGatedFeatureFlag(remoteFlag) ?? localFlag;
+  },
+);
+```
+
+Non-standard shape:
+
+```ts
+validatedVersionGatedFeatureFlag({
+  enabled: depositConfig.active ?? false,
+  minimumVersion: depositConfig.minimumVersion ?? '',
+}) ?? false;
+```
+
+UI:
+
+```ts
+const isEnabled = useSelector(selectMyFeatureEnabled);
+```
+
+## Reject
+
+- Local copies of `hasMinimumRequiredVersion` or `validatedVersionGatedFeatureFlag`
+- Inline `compare-versions` + `getVersion` for feature-flag gating outside `app/util/remoteFeatureFlag`
+- Version checks in hooks or components (`getVersion()`, `compare-versions`, or a local helper)
+- Duplicate util files under `app/components/UI/**/utils/` or `app/core/redux/slices/**/`

domains/platform/skills/feature-flags/skill.md

@@ -0,0 +1,27 @@
+---
+name: feature-flags
+description: >-
+  Version-gated remote feature flags. Use when adding, migrating, or
+  reviewing a remote or version-gated feature flag, writing a flag
+  selector, or gating UI on a flag boolean.
+maturity: stable
+base: true
+---
+
+# Feature flags
+
+Use this skill for remote and version-gated feature flags.
+
+## When to use
+
+- Adding or migrating a remote / version-gated feature flag
+- Writing or updating a flag selector
+- Gating UI or hooks on a flag boolean
+- Reviewing a PR that introduces or changes flag evaluation
+
+## Workflow
+
+1. Evaluate the flag in a selector. Return a boolean.
+2. Map a non-standard remote shape to `{ enabled, minimumVersion }` before the shared helper.
+3. Consume that boolean in UI or hooks. Do not re-run version math there.
+4. Cover the selector with collocated tests (enabled, disabled, invalid, fallback).