fix(practice): real-time progress in observer modal + numeric answer comparison

- Add currentProblemNumber and totalProblems to broadcast state
- Observer modal now shows live "Problem X of Y" updates as student progresses
- Fix answer validation to use numeric comparison (parseInt) instead of string
  comparison, so "09" correctly equals 9 (fixes red background when correct)
- Simplify MiniStartPracticeBanner to always show "Resume" for active sessions

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/src/components/classroom/SessionObserverModal.tsx

@@ -208,7 +208,8 @@ export function SessionObserverModal({
                     margin: 0,
                   })}
                 >
-                  Problem {session.completedProblems + 1} of {session.totalProblems}
+                  Problem {state?.currentProblemNumber ?? session.completedProblems + 1} of{' '}
+                  {state?.totalProblems ?? session.totalProblems}
                 </Dialog.Description>
               </div>
             </div>

apps/web/src/components/practice/ActiveSession.tsx

@@ -90,6 +90,10 @@ export interface BroadcastState {
   purpose: 'focus' | 'reinforce' | 'review' | 'challenge'
   /** Complexity data for tooltip display */
   complexity?: BroadcastComplexity
+  /** Current problem number (1-indexed for display) */
+  currentProblemNumber: number
+  /** Total problems in the session */
+  totalProblems: number
 }
 
 interface ActiveSessionProps {
@@ -191,6 +195,27 @@ function formatSkillName(category: string, skillKey: string): string {
   return `${category}: ${skillKey}`
 }
 
+/**
+ * Calculate the number of abacus columns needed to compute a problem.
+ *
+ * This considers all intermediate running totals as we progress through the terms,
+ * not just the final answer. For subtraction (e.g., 87 - 45 = 42), we need
+ * enough columns for the minuend (87), not just the answer (42).
+ */
+function calculateAbacusColumns(terms: number[]): number {
+  if (terms.length === 0) return 1
+
+  let runningTotal = 0
+  let maxAbsValue = 0
+
+  for (const term of terms) {
+    runningTotal += term
+    maxAbsValue = Math.max(maxAbsValue, Math.abs(runningTotal))
+  }
+
+  return Math.max(1, String(maxAbsValue).length)
+}
+
 /**
  * Complexity section for purpose tooltip - shows complexity bounds and actual costs
  */
@@ -465,6 +490,10 @@ function LinearProblem({
   const isPrefixSum = detectedPrefixIndex !== undefined
   const operator = isPrefixSum ? '…' : '='
 
+  // Use numeric comparison so "09" equals 9
+  const numericUserAnswer = parseInt(userAnswer, 10)
+  const answeredCorrectly = isCompleted && numericUserAnswer === correctAnswer
+
   return (
     <div
       data-component="linear-problem"
@@ -502,7 +531,7 @@ function LinearProblem({
           borderRadius: '8px',
           textAlign: 'center',
           backgroundColor: isCompleted
-            ? userAnswer === String(correctAnswer)
+            ? answeredCorrectly
               ? isDark
                 ? 'green.900'
                 : 'green.100'
@@ -513,7 +542,7 @@ function LinearProblem({
               ? 'gray.800'
               : 'gray.100',
           color: isCompleted
-            ? userAnswer === String(correctAnswer)
+            ? answeredCorrectly
               ? isDark
                 ? 'green.200'
                 : 'green.700'
@@ -647,6 +676,20 @@ export function ActiveSession({
     }
   }, [onTimingUpdate, attempt?.startTime, attempt?.accumulatedPauseMs])
 
+  // Calculate total progress across all parts (needed for broadcast state)
+  const totalProblems = useMemo(() => {
+    return plan.parts.reduce((sum, part) => sum + part.slots.length, 0)
+  }, [plan.parts])
+
+  const completedProblems = useMemo(() => {
+    let count = 0
+    for (let i = 0; i < plan.currentPartIndex; i++) {
+      count += plan.parts[i].slots.length
+    }
+    count += plan.currentSlotIndex
+    return count
+  }, [plan.parts, plan.currentPartIndex, plan.currentSlotIndex])
+
   // Notify parent of broadcast state changes for session observation
   useEffect(() => {
     if (!onBroadcastStateChange) return
@@ -694,6 +737,8 @@ export function ActiveSession({
         startedAt: attempt?.startTime ?? Date.now(),
         purpose: prevPurpose,
         complexity: extractComplexity(prevSlot),
+        currentProblemNumber: completedProblems + 1,
+        totalProblems,
       })
       return
     }
@@ -731,6 +776,8 @@ export function ActiveSession({
       startedAt: attempt.startTime,
       purpose,
       complexity: extractComplexity(slot),
+      currentProblemNumber: completedProblems + 1,
+      totalProblems,
     })
   }, [
     onBroadcastStateChange,
@@ -743,6 +790,8 @@ export function ActiveSession({
     plan.parts,
     plan.currentPartIndex,
     plan.currentSlotIndex,
+    completedProblems,
+    totalProblems,
   ])
 
   // Handle teacher abacus control events
@@ -1050,20 +1099,6 @@ export function ActiveSession({
   const currentSlot = currentPart?.slots[currentSlotIndex] as ProblemSlot | undefined
   const sessionHealth = plan.sessionHealth as SessionHealth | null
 
-  // Calculate total progress across all parts
-  const totalProblems = useMemo(() => {
-    return parts.reduce((sum, part) => sum + part.slots.length, 0)
-  }, [parts])
-
-  const completedProblems = useMemo(() => {
-    let count = 0
-    for (let i = 0; i < currentPartIndex; i++) {
-      count += parts[i].slots.length
-    }
-    count += currentSlotIndex
-    return count
-  }, [parts, currentPartIndex, currentSlotIndex])
-
   // Check for session completion
   useEffect(() => {
     if (currentPartIndex >= parts.length) {
@@ -1777,7 +1812,7 @@ export function ActiveSession({
               {currentPart.type === 'abacus' && !showHelpOverlay && (problemHeight ?? 0) > 0 && (
                 <AbacusDock
                   id="practice-abacus"
-                  columns={String(Math.abs(attempt.problem.answer)).length}
+                  columns={calculateAbacusColumns(attempt.problem.terms)}
                   interactive={true}
                   showNumbers={false}
                   animated={true}

apps/web/src/components/practice/MiniStartPracticeBanner.tsx

@@ -14,14 +14,10 @@ interface MiniStartPracticeBannerProps {
   sessionMode: SessionMode | null
   /** Current activity status */
   activity: StudentActivity | null
-  /** Whether the viewer is a teacher (affects "Watch" vs "Resume" for active sessions) */
-  isTeacher?: boolean
   /** Called when "Start" is clicked - should open StartPracticeModal */
   onStartPractice: () => void
   /** Called when "Resume" is clicked - navigates to active session */
   onResumePractice: () => void
-  /** Called when "Watch" is clicked - opens session observer */
-  onWatchSession: () => void
 }
 
 // ============================================================================
@@ -95,28 +91,10 @@ function getIdleModeConfig(sessionMode: SessionMode): ModeConfig {
   }
 }
 
-function getActiveSessionConfig(activity: StudentActivity, isTeacher: boolean): ModeConfig {
+function getActiveSessionConfig(activity: StudentActivity): ModeConfig {
   const progress = activity.sessionProgress
   const progressText = progress ? `${progress.current}/${progress.total} problems` : 'In progress'
 
-  if (isTeacher) {
-    // Teacher sees "Watch" option
-    return {
-      icon: '👁',
-      label: 'Practicing now',
-      sublabel: progressText,
-      buttonLabel: 'Watch',
-      bgGradient: {
-        light:
-          'linear-gradient(135deg, rgba(139, 92, 246, 0.06) 0%, rgba(59, 130, 246, 0.04) 100%)',
-        dark: 'linear-gradient(135deg, rgba(139, 92, 246, 0.12) 0%, rgba(59, 130, 246, 0.08) 100%)',
-      },
-      borderColor: { light: '#8b5cf6', dark: '#7c3aed' },
-      textColor: { light: '#6d28d9', dark: '#c4b5fd' },
-      buttonGradient: 'linear-gradient(135deg, #8b5cf6 0%, #7c3aed 100%)',
-    }
-  } else {
-    // Parent/student sees "Resume" option
   return {
     icon: '▶️',
     label: 'Session in progress',
@@ -130,7 +108,6 @@ function getActiveSessionConfig(activity: StudentActivity, isTeacher: boolean):
     textColor: { light: '#166534', dark: '#86efac' },
     buttonGradient: 'linear-gradient(135deg, #22c55e 0%, #16a34a 100%)',
   }
-  }
 }
 
 // ============================================================================
@@ -142,18 +119,15 @@ function getActiveSessionConfig(activity: StudentActivity, isTeacher: boolean):
  *
  * Shows different content based on state:
  * - Idle + session mode: Shows session mode info with "Start" CTA
- * - Active session (teacher): Shows "Watch" to observe
- * - Active session (parent): Shows "Resume" to continue
+ * - Active session: Shows "Resume" to continue/observe the session
  *
  * Designed to fit above the Overview/Notes tabs.
  */
 export function MiniStartPracticeBanner({
   sessionMode,
   activity,
-  isTeacher = false,
   onStartPractice,
   onResumePractice,
-  onWatchSession,
 }: MiniStartPracticeBannerProps) {
   const { resolvedTheme } = useTheme()
   const isDark = resolvedTheme === 'dark'
@@ -165,8 +139,8 @@ export function MiniStartPracticeBanner({
   let handleClick: () => void
 
   if (isPracticing) {
-    config = getActiveSessionConfig(activity, isTeacher)
-    handleClick = isTeacher ? onWatchSession : onResumePractice
+    config = getActiveSessionConfig(activity)
+    handleClick = onResumePractice
   } else if (sessionMode) {
     config = getIdleModeConfig(sessionMode)
     handleClick = onStartPractice
@@ -179,7 +153,7 @@ export function MiniStartPracticeBanner({
     <div
       data-component="mini-start-practice-banner"
       data-mode={isPracticing ? 'active' : sessionMode?.type}
-      data-variant={isPracticing ? (isTeacher ? 'watch' : 'resume') : 'start'}
+      data-variant={isPracticing ? 'resume' : 'start'}
       className={css({
         display: 'flex',
         alignItems: 'center',
@@ -246,9 +220,7 @@ export function MiniStartPracticeBanner({
       {/* Action button */}
       <button
         type="button"
-        data-action={
-          isPracticing ? (isTeacher ? 'watch-session' : 'resume-practice') : 'start-practice'
-        }
+        data-action={isPracticing ? 'resume-practice' : 'start-practice'}
         onClick={handleClick}
         className={css({
           display: 'flex',

apps/web/src/components/practice/NotesModal.tsx

@@ -9,7 +9,6 @@ import { FamilyCodeDisplay } from '@/components/family'
 import { Z_INDEX } from '@/constants/zIndex'
 import { usePageTransition } from '@/contexts/PageTransitionContext'
 import { useTheme } from '@/contexts/ThemeContext'
-import { useMyClassroom } from '@/hooks/useClassroom'
 import { usePlayerCurriculumQuery } from '@/hooks/usePlayerCurriculum'
 import { useSessionMode } from '@/hooks/useSessionMode'
 import { useStudentActions, type StudentActionData } from '@/hooks/useStudentActions'
@@ -159,8 +158,6 @@ export function NotesModal({
   // ========== Additional data for Overview tab ==========
   const { data: curriculumData } = usePlayerCurriculumQuery(student.id)
   const { data: sessionMode } = useSessionMode(student.id)
-  const { data: classroom } = useMyClassroom()
-  const isTeacher = !!classroom
   const updatePlayer = useUpdatePlayer() // For notes only
 
   // ========== Stakeholder data for Relationships tab ==========
@@ -215,15 +212,6 @@ export function NotesModal({
     router.push(`/practice/${student.id}`)
   }, [onClose, router, student.id])
 
-  const handleBannerWatchSession = useCallback(() => {
-    // Session observer is rendered at parent level to avoid z-index issues
-    // Close this modal first so the observer modal appears on top
-    if (onObserveSession && student.activity?.sessionId) {
-      onClose()
-      onObserveSession(student.activity.sessionId)
-    }
-  }, [onObserveSession, student.activity?.sessionId, onClose])
-
   // ========== Effects ==========
 
   // Reset state when modal opens/closes or student changes
@@ -646,10 +634,8 @@ export function NotesModal({
         <MiniStartPracticeBanner
           sessionMode={sessionMode ?? null}
           activity={activity}
-          isTeacher={isTeacher}
           onStartPractice={handleBannerStartPractice}
           onResumePractice={handleBannerResumePractice}
-          onWatchSession={handleBannerWatchSession}
         />
 
         {/* Tab bar - show if Overview has content or if we have stakeholder data */}

apps/web/src/components/practice/VerticalProblem.tsx

@@ -92,8 +92,10 @@ export function VerticalProblem({
     correctAnswer?.toString().length || 1
   )
 
-  const isCorrect = isCompleted && userAnswer === correctAnswer?.toString()
-  const isIncorrect = isCompleted && userAnswer !== correctAnswer?.toString()
+  // Use numeric comparison so "09" equals 9
+  const numericUserAnswer = parseInt(userAnswer, 10)
+  const isCorrect = isCompleted && correctAnswer !== undefined && numericUserAnswer === correctAnswer
+  const isIncorrect = isCompleted && correctAnswer !== undefined && numericUserAnswer !== correctAnswer
 
   const fontSize = size === 'large' ? '2rem' : '1.5rem'
   const cellWidth = size === 'large' ? '1.8rem' : '1.4rem'

apps/web/src/hooks/useSessionBroadcast.ts

@@ -84,6 +84,8 @@ export function useSessionBroadcast(
       },
       purpose: currentState.purpose,
       complexity: currentState.complexity,
+      currentProblemNumber: currentState.currentProblemNumber,
+      totalProblems: currentState.totalProblems,
     }
 
     socketRef.current.emit('practice-state', event)

apps/web/src/hooks/useSessionObserver.ts

@@ -57,6 +57,10 @@ export interface ObservedSessionState {
   complexity?: ObservedComplexity
   /** When this state was received */
   receivedAt: number
+  /** Current problem number (1-indexed for display) */
+  currentProblemNumber: number
+  /** Total problems in the session */
+  totalProblems: number
 }
 
 interface UseSessionObserverResult {
@@ -176,6 +180,8 @@ export function useSessionObserver(
         purpose: data.purpose,
         complexity: data.complexity,
         receivedAt: Date.now(),
+        currentProblemNumber: data.currentProblemNumber,
+        totalProblems: data.totalProblems,
       })
     })
 

apps/web/src/lib/classroom/socket-events.ts

@@ -151,6 +151,10 @@ export interface PracticeStateEvent {
   purpose: 'focus' | 'reinforce' | 'review' | 'challenge'
   /** Complexity data for tooltip display */
   complexity?: BroadcastComplexity
+  /** Current problem number (1-indexed for display) */
+  currentProblemNumber: number
+  /** Total problems in the session */
+  totalProblems: number
 }
 
 export interface TutorialStateEvent {