fix: return empty string for defaultFeature when enabled list is empty

Avoids inconsistency where defaultFeature would resolve to 'dashboard'
but isFeatureEnabled('dashboard') returns false. When no features are
enabled, defaultFeature is now an empty string.

Author: bjcoombs

frontend/src/hooks/__tests__/use-tenant-features.test.ts

@@ -138,4 +138,22 @@ describe('useTenantFeatures', () => {
     // Should fall back to first enabled feature, not the disabled default
     expect(result.current.defaultFeature).toBe('accounts')
   })
+
+  it('returns empty string for defaultFeature when no features are enabled', () => {
+    vi.mocked(useTenantContext).mockReturnValue(
+      makeContext({
+        tenantConfig: {
+          features: {
+            enabled: [],
+          },
+        },
+      }),
+    )
+
+    const { result } = renderHook(() => useTenantFeatures())
+
+    // No enabled features — defaultFeature must not point to a disabled feature
+    expect(result.current.defaultFeature).toBe('')
+    expect(result.current.isFeatureEnabled('dashboard')).toBe(false)
+  })
 })

frontend/src/hooks/use-tenant-features.ts

@@ -22,11 +22,12 @@ export function useTenantFeatures(): TenantFeaturesResult {
     const enabledFeatures = config.features?.enabled ?? [...ALL_FEATURES]
     const enabledSet = new Set<string>(enabledFeatures)
 
-    // Fall back to the first enabled feature if the configured default is not in the enabled list
+    // Fall back to the first enabled feature if the configured default is not in the enabled list.
+    // When no features are enabled at all, defaultFeature is an empty string (no valid default).
     const configuredDefault = config.features?.defaultFeature ?? 'dashboard'
     const defaultFeature = enabledSet.has(configuredDefault)
       ? configuredDefault
-      : (enabledFeatures[0] ?? 'dashboard')
+      : (enabledFeatures[0] ?? '')
 
     return {
       isFeatureEnabled: (feature: string) => enabledSet.has(feature),