fix: respect operator-specific scaffolding in mastery+mixed mode

Fix bug where scaffolding settings (answer boxes, carry boxes, etc.) weren't being respected in mastery+mixed mode (addition+subtraction).

**Root cause:**
validation.ts was reading from formState.displayRules (general field) instead of formState.additionDisplayRules and formState.subtractionDisplayRules (operator-specific fields). Additionally, it only allowed overriding problemNumbers and cellBorders, ignoring all other scaffolding settings.

**Fix:**
- Read from operator-specific display rules (additionDisplayRules, subtractionDisplayRules) when they exist
- Fall back to general displayRules if operator-specific rules aren't set
- Allow ALL display rule fields to override skill's recommendedScaffolding
- Add debug logging to trace which rules are being used

**Testing:**
1. Set mode to "mastery" with operator "mixed" (addition+subtraction)
2. Change scaffolding setting (e.g., answer boxes from "always" to "never")
3. Verify the preview now respects the custom scaffolding setting

Fixes validation.ts:288-318

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

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

apps/web/.claude/settings.local.json

@@ -48,7 +48,5 @@
     "ask": []
   },
   "enableAllProjectMcpServers": true,
-  "enabledMcpjsonServers": [
-    "sqlite"
-  ]
+  "enabledMcpjsonServers": ["sqlite"]
 }

apps/web/src/app/create/worksheets/hooks/useWorksheetState.ts

@@ -111,7 +111,10 @@ export function useWorksheetState(
 
       if (affectsProblems) {
         newState.seed = Date.now() % 2147483647
-        console.log('[useWorksheetState] Problem settings changed - generated new seed:', newState.seed)
+        console.log(
+          '[useWorksheetState] Problem settings changed - generated new seed:',
+          newState.seed
+        )
       }
 
       console.log('[useWorksheetState] New formState:', {

apps/web/src/app/create/worksheets/validation.ts

@@ -286,29 +286,36 @@ export function validateWorksheetConfig(formState: WorksheetFormState): Validati
         const subSkill = getSkillById(subSkillId as any)
 
         if (addSkill?.recommendedScaffolding && subSkill?.recommendedScaffolding) {
-          // Merge user's displayRules with skill's recommended scaffolding
-          // User's displayRules take precedence for problemNumbers and cellBorders (layout options)
-          const userDisplayRules: Partial<DisplayRules> = formState.displayRules || {}
+          // Merge user's operator-specific displayRules with skill's recommended scaffolding
+          // User's rules (if set) take precedence over skill's recommendations
+          // Fall back to general displayRules if operator-specific rules don't exist
+          const userAdditionRules: Partial<DisplayRules> =
+            (formState as any).additionDisplayRules || formState.displayRules || {}
+          const userSubtractionRules: Partial<DisplayRules> =
+            (formState as any).subtractionDisplayRules || formState.displayRules || {}
+
+          console.log('[MIXED MODE SCAFFOLDING] User rules:', {
+            additionRules: userAdditionRules,
+            subtractionRules: userSubtractionRules,
+            generalRules: formState.displayRules,
+          })
 
           config = {
             ...baseConfig,
             additionDisplayRules: {
               ...addSkill.recommendedScaffolding,
-              // Override layout options with user's choices
-              problemNumbers:
-                userDisplayRules.problemNumbers ?? addSkill.recommendedScaffolding.problemNumbers,
-              cellBorders:
-                userDisplayRules.cellBorders ?? addSkill.recommendedScaffolding.cellBorders,
+              ...userAdditionRules, // User's custom rules override skill's recommendations
             },
             subtractionDisplayRules: {
               ...subSkill.recommendedScaffolding,
-              // Override layout options with user's choices
-              problemNumbers:
-                userDisplayRules.problemNumbers ?? subSkill.recommendedScaffolding.problemNumbers,
-              cellBorders:
-                userDisplayRules.cellBorders ?? subSkill.recommendedScaffolding.cellBorders,
+              ...userSubtractionRules, // User's custom rules override skill's recommendations
             },
           } as any
+
+          console.log('[MIXED MODE SCAFFOLDING] Final config:', {
+            additionDisplayRules: config.additionDisplayRules,
+            subtractionDisplayRules: config.subtractionDisplayRules,
+          })
         } else {
           console.log('[MIXED MODE SCAFFOLDING] Missing recommendedScaffolding', {
             addSkill: addSkill?.name,