feat: create unified difficulty interface with 2-tab selector

Replace 3-way mode tabs (Smart/Manual/Mastery) with unified interface:
- Smart and Mastery are now "quick presets" via 2-tab selector
- Manual controls (thermometers) always visible for customization
- All modes share same displayRules system (1:1 correspondence)

Changes:
- Add DifficultyMethodSelector component with tab-style UI
- Update ConfigPanel to use 2-tab selector
- Smart/Mastery populate the always-visible display controls
- Preserve displayRules when switching between methods

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/create/worksheets/addition/components/ConfigPanel.tsx

@@ -3,14 +3,13 @@
 import { stack } from '../../../../../../styled-system/patterns'
 import type { WorksheetFormState } from '../types'
 import { defaultAdditionConfig } from '@/app/create/worksheets/config-schemas'
-import { ModeSelector } from './ModeSelector'
+import { DifficultyMethodSelector } from './DifficultyMethodSelector'
 import { StudentNameInput } from './config-panel/StudentNameInput'
-import { DigitRangeSection } from './config-panel/DigitRangeSection'
 import { OperatorSection } from './config-panel/OperatorSection'
 import { ProgressiveDifficultyToggle } from './config-panel/ProgressiveDifficultyToggle'
 import { SmartModeControls } from './config-panel/SmartModeControls'
-import { ManualModeControls } from './config-panel/ManualModeControls'
 import { MasteryModePanel } from './config-panel/MasteryModePanel'
+import { DisplayControlsPanel } from './DisplayControlsPanel'
 
 interface ConfigPanelProps {
   formState: WorksheetFormState
@@ -19,55 +18,23 @@ interface ConfigPanelProps {
 }
 
 export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanelProps) {
-  // Handler for mode switching
-  const handleModeChange = (newMode: 'smart' | 'manual' | 'mastery') => {
-    if (formState.mode === newMode) {
+  // Handler for difficulty method switching (smart vs mastery)
+  const handleMethodChange = (newMethod: 'smart' | 'mastery') => {
+    const currentMethod = formState.mode === 'mastery' ? 'mastery' : 'smart'
+    if (currentMethod === newMethod) {
       return // No change needed
     }
 
-    if (newMode === 'smart') {
-      // Switching to Smart mode
-      // Use current displayRules if available, otherwise default to earlyLearner
-      const displayRules = formState.displayRules ?? defaultAdditionConfig.displayRules
+    // Preserve displayRules when switching
+    const displayRules = formState.displayRules ?? defaultAdditionConfig.displayRules
+
+    if (newMethod === 'smart') {
       onChange({
         mode: 'smart',
         displayRules,
         difficultyProfile: 'earlyLearner',
       } as unknown as Partial<WorksheetFormState>)
-    } else if (newMode === 'manual') {
-      // Switching to Manual mode
-      // Convert current displayRules to boolean flags if available
-      let booleanFlags = {
-        showCarryBoxes: true,
-        showAnswerBoxes: true,
-        showPlaceValueColors: true,
-        showTenFrames: false,
-        showProblemNumbers: true,
-        showCellBorder: true,
-        showTenFramesForAll: false,
-      }
-
-      if (formState.displayRules) {
-        // Convert 'always' to true, everything else to false
-        booleanFlags = {
-          showCarryBoxes: formState.displayRules.carryBoxes === 'always',
-          showAnswerBoxes: formState.displayRules.answerBoxes === 'always',
-          showPlaceValueColors: formState.displayRules.placeValueColors === 'always',
-          showTenFrames: formState.displayRules.tenFrames === 'always',
-          showProblemNumbers: formState.displayRules.problemNumbers === 'always',
-          showCellBorder: formState.displayRules.cellBorders === 'always',
-          showTenFramesForAll: false,
-        }
-      }
-
-      onChange({
-        mode: 'manual',
-        ...booleanFlags,
-      } as unknown as Partial<WorksheetFormState>)
     } else {
-      // Switching to Mastery mode
-      // Mastery mode uses Smart mode under the hood with skill-based configuration
-      const displayRules = formState.displayRules ?? defaultAdditionConfig.displayRules
       onChange({
         mode: 'mastery',
         displayRules,
@@ -75,6 +42,9 @@ export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanel
     }
   }
 
+  // Determine current method for selector
+  const currentMethod = formState.mode === 'mastery' ? 'mastery' : 'smart'
+
   return (
     <div data-component="config-panel" className={stack({ gap: '3' })}>
       {/* Student Name */}
@@ -84,13 +54,6 @@ export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanel
         isDark={isDark}
       />
 
-      {/* Digit Range Selector */}
-      <DigitRangeSection
-        digitRange={formState.digitRange}
-        onChange={(digitRange) => onChange({ digitRange })}
-        isDark={isDark}
-      />
-
       {/* Operator Selector */}
       <OperatorSection
         operator={formState.operator}
@@ -98,33 +61,29 @@ export function ConfigPanel({ formState, onChange, isDark = false }: ConfigPanel
         isDark={isDark}
       />
 
-      {/* Progressive Difficulty Toggle - Available for all modes */}
+      {/* Progressive Difficulty Toggle */}
       <ProgressiveDifficultyToggle
         interpolate={formState.interpolate}
         onChange={(interpolate) => onChange({ interpolate })}
         isDark={isDark}
       />
 
-      {/* Mode Selector Tabs with description */}
-      <ModeSelector
-        currentMode={formState.mode ?? 'smart'}
-        onChange={handleModeChange}
+      {/* Display Controls - Always visible for manual adjustment */}
+      <DisplayControlsPanel formState={formState} onChange={onChange} isDark={isDark} />
+
+      {/* Difficulty Method Selector (Smart vs Mastery) */}
+      <DifficultyMethodSelector
+        currentMethod={currentMethod}
+        onChange={handleMethodChange}
         isDark={isDark}
       />
 
-      {/* Mode-specific controls - no wrapper, let controls style themselves */}
-      {/* Smart Mode Controls */}
-      {(!formState.mode || formState.mode === 'smart') && (
+      {/* Method-specific preset controls */}
+      {currentMethod === 'smart' && (
         <SmartModeControls formState={formState} onChange={onChange} isDark={isDark} />
       )}
 
-      {/* Manual Mode Controls */}
-      {formState.mode === 'manual' && (
-        <ManualModeControls formState={formState} onChange={onChange} isDark={isDark} />
-      )}
-
-      {/* Mastery Mode Controls */}
-      {formState.mode === 'mastery' && (
+      {currentMethod === 'mastery' && (
         <MasteryModePanel formState={formState} onChange={onChange} isDark={isDark} />
       )}
     </div>

apps/web/src/app/create/worksheets/addition/components/DifficultyMethodSelector.tsx

@@ -0,0 +1,104 @@
+'use client'
+
+import { css } from '../../../../../../styled-system/css'
+
+interface DifficultyMethodSelectorProps {
+  currentMethod: 'smart' | 'mastery'
+  onChange: (method: 'smart' | 'mastery') => void
+  isDark?: boolean
+}
+
+export function DifficultyMethodSelector({
+  currentMethod,
+  onChange,
+  isDark = false,
+}: DifficultyMethodSelectorProps) {
+  return (
+    <div data-component="difficulty-method-selector">
+      {/* Tab buttons */}
+      <div
+        className={css({
+          display: 'grid',
+          gridTemplateColumns: '1fr 1fr',
+          gap: '0',
+          bg: isDark ? 'gray.800' : 'gray.100',
+          p: '1',
+          rounded: 'lg',
+        })}
+      >
+        {/* Smart Difficulty Tab */}
+        <button
+          type="button"
+          data-action="select-smart"
+          onClick={() => onChange('smart')}
+          className={css({
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            gap: '2',
+            px: '4',
+            py: '2.5',
+            bg: currentMethod === 'smart' ? (isDark ? 'gray.700' : 'white') : 'transparent',
+            color: currentMethod === 'smart' ? (isDark ? 'gray.100' : 'gray.900') : (isDark ? 'gray.400' : 'gray.600'),
+            fontWeight: currentMethod === 'smart' ? 'semibold' : 'medium',
+            fontSize: 'sm',
+            rounded: 'md',
+            cursor: 'pointer',
+            transition: 'all 0.2s',
+            boxShadow: currentMethod === 'smart' ? (isDark ? '0 1px 3px rgba(0,0,0,0.3)' : '0 1px 3px rgba(0,0,0,0.1)') : 'none',
+            _hover: {
+              color: isDark ? 'gray.200' : 'gray.700',
+            },
+          })}
+        >
+          <span>🎯</span>
+          <span>Smart Difficulty</span>
+        </button>
+
+        {/* Mastery Progression Tab */}
+        <button
+          type="button"
+          data-action="select-mastery"
+          onClick={() => onChange('mastery')}
+          className={css({
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            gap: '2',
+            px: '4',
+            py: '2.5',
+            bg: currentMethod === 'mastery' ? (isDark ? 'gray.700' : 'white') : 'transparent',
+            color: currentMethod === 'mastery' ? (isDark ? 'gray.100' : 'gray.900') : (isDark ? 'gray.400' : 'gray.600'),
+            fontWeight: currentMethod === 'mastery' ? 'semibold' : 'medium',
+            fontSize: 'sm',
+            rounded: 'md',
+            cursor: 'pointer',
+            transition: 'all 0.2s',
+            boxShadow: currentMethod === 'mastery' ? (isDark ? '0 1px 3px rgba(0,0,0,0.3)' : '0 1px 3px rgba(0,0,0,0.1)') : 'none',
+            _hover: {
+              color: isDark ? 'gray.200' : 'gray.700',
+            },
+          })}
+        >
+          <span>🎓</span>
+          <span>Mastery Progression</span>
+        </button>
+      </div>
+
+      {/* Description text */}
+      <div
+        className={css({
+          mt: '2',
+          px: '1',
+          fontSize: 'xs',
+          color: isDark ? 'gray.400' : 'gray.600',
+          textAlign: 'center',
+        })}
+      >
+        {currentMethod === 'smart'
+          ? 'Choose a difficulty preset, then customize display options below'
+          : 'Follow a structured skill progression with recommended scaffolding'}
+      </div>
+    </div>
+  )
+}