🤖 refactor: simplify stats tab experiment to toggle

[ThomasK33]

Convert the Stats Tab experiment setting from a 3-option dropdown to a simple on/off toggle, matching the UX pattern used for other experiments.

Changes:

• Replace dropdown with Switch component in ExperimentsSection
• Simplify FeatureFlagsContext API: setStatsTabOverride → setStatsTabEnabled
• Remove PostHog implementation details from user-facing description
• Backend schema unchanged (preserves flexibility)

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📋 Implementation Plan

Plan: Simplify Stats Tab Experiment Toggle

Goal

Convert the Stats Tab experiment from a 3-option dropdown (Default (experiment), Always on, Always off) to a simple on/off toggle, matching the pattern used for other experiments like Post-Compaction Context.

Current State

• UI: ExperimentsSection.tsx renders StatsTabOverrideRow with a <select> dropdown containing 3 options
• Frontend context: FeatureFlagsContext.tsx exposes StatsTabState with variant, override, and enabled fields
• Backend service: featureFlagService.ts fetches PostHog variant and applies 3-way override logic
• Storage: Backend stores override in ~/.mux/config.json under featureFlagOverrides[stats_tab_v1]
• Schema: api.ts defines StatsTabOverrideSchema = z.enum(["default", "on", "off"])

Proposed Changes

1. Frontend: Replace dropdown with toggle (~-30 LoC)

File: src/browser/components/Settings/sections/ExperimentsSection.tsx

• Replace StatsTabOverrideRow with a simpler row using <Switch>:
  • Label: "Stats tab"
  • Description: "Show timing statistics in the right sidebar" (no PostHog mention)
  • Toggle reflects statsTabState.enabled
  • Toggle calls setStatsTabOverride("on" | "off") based on new state

2. Context: Simplify setStatsTabOverride signature (~-5 LoC)

File: src/browser/contexts/FeatureFlagsContext.tsx

• setStatsTabOverride(override: StatsTabOverride) → setStatsTabEnabled(enabled: boolean)
• Internally convert boolean to "on" | "off" when calling backend
• No more "default" option exposed to UI

3. Backend & Schema: Unchanged

The backend already stores "on" | "off" | "default" and computes enabled based on PostHog variant + override. We keep this to allow future flexibility, but the UI will only ever set "on" or "off" (never "default").

Alternative: Migrate to experiments system

We could move Stats Tab to the existing EXPERIMENTS + ExperimentsContext pattern (localStorage-based), but:

• That would lose PostHog A/B tracking capability
• Would require data migration from config.json to localStorage
• The current feature flag service is already correct; simplifying the UI is sufficient

This alternative is not recommended for this change.

Net LoC Estimate

~-25 lines (remove dropdown complexity, add simpler toggle, simplify context API)

Files Modified

1. src/browser/components/Settings/sections/ExperimentsSection.tsx
2. src/browser/contexts/FeatureFlagsContext.tsx

Testing

• Manual: Open Settings → Experiments → verify toggle works
• Existing typecheck and lint will catch regressions

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Generated with mux • Model: anthropic:claude-opus-4-5 • Thinking: high