feat: add capability-aware feature flag system#3229
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rossnelson wants to merge 5 commits intomainfrom
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Add a typed feature flag store using persistStore for localStorage persistence and cross-tab sync. Exports featureFlags map store, isFeatureFlagEnabled derived helper, setFeatureFlag setter, and LocalFeatureFlag guard component for declarative usage. Includes storage event listener for cross-tab localStorage detection.
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Replace the localStorage-only LocalFeatureFlag component with a CapabilityGuard that checks server capabilities first, falling back to localStorage when the capability is absent. Extends Capabilities type with serverlessWorkers for forward compatibility. Adds isCapabilityEnabled factory and withLocalFallback helper to capability-enablement.ts.
rossnelson
changed the title
Replace the JSON map store with per-flag persistStore instances keyed
as featureFlags.<capabilityKey>. Removes isFeatureFlagEnabled and the
FeatureFlag type in favour of using keyof Capabilities directly.
Enable a flag via: localStorage.setItem('featureFlags.serverlessWorkers', 'true')
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| const serverValue = $page.data?.systemInfo?.capabilities?.[capabilityKey]; | ||
| if (serverValue !== undefined && serverValue !== null) { | ||
| return Boolean(serverValue); | ||
| } |
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Curious why we need this when below we do the same capability check in isCapabilityEnabled
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It's not a redundant check. It ensures that the system-info value takes precedence. But i can see how the way its written makes it seem redundant. Ill update it to be more clear.
Replace the separate helper with inlined guard-clause logic and ?? operator to make the server-first, localStorage-fallback intent self-evident.
laurakwhit
reviewed
Mar 19, 2026
| ): Readable<boolean> { | ||
| if (!LOCAL_OVERRIDE_CAPABILITIES.has(key)) { | ||
| return derived(page, ($page) => | ||
| Boolean($page.data?.systemInfo?.capabilities?.[key]), |
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We also have page.data.namespace.namespaceInfo?.capabilities which is where workerHeartbeats is currently enabled/disabled. Maybe we want a distinction between isSystemCapabilityEnabled and isNamespaceCapabilityEnabled?
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Summary
featureFlagspersistStore holding aRecord<string, boolean>under thefeatureFlagslocalStorage key — the local override layerCapabilitiestype withserverlessWorkers?: boolean | nullfor forward compatibility with the protowithLocalFallbackandisCapabilityEnabledtocapability-enablement.ts— server capability is authoritative when present, localStorage is the fallback when absentCapabilityGuardcomponent for declarative feature gatingCleanShot.2026-03-19.at.09.51.55.mp4
How it works
truefalsetruetrueUsage
Enable locally until the server reports the capability:
Adding a new capability with local override = one line in
CAPABILITY_FLAG_MAP.Test plan
pnpm lintpasses with no new errorspnpm checkpasses with no new errorspnpm test -- --runpasses all unit tests with no regressionsCapabilityGuardrenders children when capability/flag enabled, fallback when disabled, nothing when disabled with no fallbackfalseoverrides localStoragetrue