please fix mobile?

src/app/exercise/[id]/ExercisePageClient.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { use, useEffect, useState } from 'react';
+import { use, useEffect, useRef, useState } from 'react';
 import { usePathname, useRouter } from 'next/navigation';
 import { useExerciseContext } from '@/state/ExerciseContext';
 import { getExercise, getAllExercises } from '@/exercises/registry';
@@ -150,6 +150,10 @@ export default function ExercisePageClient({ params }: { params: Promise<{ id: s
   const pathname = usePathname();
   const [isMobile, setIsMobile] = useState(false);
   const [activeMobileTab, setActiveMobileTab] = useState<'source' | 'viz' | 'log' | 'misc'>('source');
+  const mobileShellRef = useRef<HTMLDivElement | null>(null);
+  const mobileWorkspacePanelRef = useRef<HTMLDivElement | null>(null);
+  const mobileDirectionsRef = useRef<HTMLDivElement | null>(null);
+  const mobileBottomDockRef = useRef<HTMLDivElement | null>(null);
 
   useEffect(() => {
     if (typeof window === 'undefined') return;
@@ -205,6 +209,67 @@ export default function ExercisePageClient({ params }: { params: Promise<{ id: s
     setActiveMobileTab('source');
   }, [id]);
 
+  useEffect(() => {
+    if (!isMobile) {
+      mobileShellRef.current?.style.removeProperty('--mobile-workspace-panel-height');
+      return;
+    }
+
+    const shellElement = mobileShellRef.current;
+    const panelElement = mobileWorkspacePanelRef.current;
+    const directionsElement = mobileDirectionsRef.current;
+    const bottomDockElement = mobileBottomDockRef.current;
+
+    if (!shellElement || !panelElement || !directionsElement || !bottomDockElement) {
+      return;
+    }
+
+    let frameId = 0;
+
+    const syncPanelHeight = () => {
+      frameId = 0;
+      const shellRect = shellElement.getBoundingClientRect();
+      const panelRect = panelElement.getBoundingClientRect();
+      const bottomDockRect = bottomDockElement.getBoundingClientRect();
+      const shellStyles = window.getComputedStyle(shellElement);
+      const shellGap = parseFloat(shellStyles.rowGap || shellStyles.gap || '0') || 0;
+      const availableHeight = Math.floor(bottomDockRect.top - panelRect.top - shellGap);
+      const maxAvailableHeight = Math.floor(shellRect.bottom - panelRect.top);
+      const nextHeight = Math.max(0, Math.min(availableHeight, maxAvailableHeight));
+      shellElement.style.setProperty('--mobile-workspace-panel-height', `${nextHeight}px`);
+    };
+
+    const queueSyncPanelHeight = () => {
+      if (frameId !== 0) return;
+      frameId = window.requestAnimationFrame(syncPanelHeight);
+    };
+
+    queueSyncPanelHeight();
+
+    const observer = new ResizeObserver(() => {
+      queueSyncPanelHeight();
+    });
+
+    observer.observe(shellElement);
+    observer.observe(directionsElement);
+    observer.observe(bottomDockElement);
+
+    window.addEventListener('resize', queueSyncPanelHeight);
+    window.visualViewport?.addEventListener('resize', queueSyncPanelHeight);
+    window.visualViewport?.addEventListener('scroll', queueSyncPanelHeight);
+
+    return () => {
+      observer.disconnect();
+      window.removeEventListener('resize', queueSyncPanelHeight);
+      window.visualViewport?.removeEventListener('resize', queueSyncPanelHeight);
+      window.visualViewport?.removeEventListener('scroll', queueSyncPanelHeight);
+      if (frameId !== 0) {
+        window.cancelAnimationFrame(frameId);
+      }
+      shellElement.style.removeProperty('--mobile-workspace-panel-height');
+    };
+  }, [activeMobileTab, isMobile]);
+
   useEffect(() => {
     const mainElement = document.querySelector('#app-body > main');
     const appElement = document.getElementById('app');
@@ -447,8 +512,10 @@ export default function ExercisePageClient({ params }: { params: Promise<{ id: s
 
   if (isMobile) {
     return (
-      <div className="mobile-exercise-shell">
-        <ExerciseDirectionsPanel />
+      <div className="mobile-exercise-shell" ref={mobileShellRef}>
+        <div ref={mobileDirectionsRef}>
+          <ExerciseDirectionsPanel />
+        </div>
 
         <section className="mobile-workspace">
           <div className="mobile-workspace-tabs" role="tablist" aria-label="Exercise workspace">
@@ -490,7 +557,7 @@ export default function ExercisePageClient({ params }: { params: Promise<{ id: s
             </button>
           </div>
 
-          <div className="mobile-workspace-panel">
+          <div className="mobile-workspace-panel" ref={mobileWorkspacePanelRef}>
             {activeMobileTab === 'source' && <SourcePanel showDescription={false} />}
             {activeMobileTab === 'viz' && (
               <ErrorBoundary>
@@ -509,7 +576,7 @@ export default function ExercisePageClient({ params }: { params: Promise<{ id: s
           </div>
         </section>
 
-        <div className="mobile-bottom-dock">
+        <div className="mobile-bottom-dock" ref={mobileBottomDockRef}>
           <ErrorBoundary>
             <InputPanel showToolkit={false} />
           </ErrorBoundary>

src/app/globals.css

@@ -980,7 +980,6 @@ button.link-button:focus-visible,
 
   .mobile-workspace {
     min-height: 0;
-    flex: 1;
     display: flex;
     flex-direction: column;
     gap: 0.5rem;
@@ -1022,15 +1021,18 @@ button.link-button:focus-visible,
 
   .mobile-workspace-panel {
     display: flex;
-    flex: 1 1 auto;
+    flex: 0 0 auto;
     flex-direction: column;
+    height: var(--mobile-workspace-panel-height, auto);
+    max-height: var(--mobile-workspace-panel-height, none);
     min-height: 0;
     overflow: hidden;
   }
 
   .mobile-workspace-panel > .panel {
-    flex: 1 1 auto;
-    height: auto;
+    flex: 1 1 100%;
+    height: 100%;
+    max-height: 100%;
     min-height: 0;
   }
 

src/components/panels/InputPanel/InputPanel.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useState } from 'react';
+import { useEffect, useState } from 'react';
 import { useExerciseContext } from '@/state/ExerciseContext';
 import StepControls from './inputs/StepControls';
 import TextHexInput from './inputs/TextHexInput';
@@ -15,10 +15,31 @@ import AsmStepInput from './inputs/AsmStepInput';
 import AsmQuizInput from './inputs/AsmQuizInput';
 import Toolkit from './Toolkit';
 
+const MOBILE_BREAKPOINT = '(max-width: 900px)';
+
 export default function InputPanel({ showToolkit = true }: { showToolkit?: boolean }) {
   const { currentExercise, asmEmulator, state } = useExerciseContext();
   const ex = currentExercise;
   const [collapsed, setCollapsed] = useState(false);
+  const [isMobile, setIsMobile] = useState(false);
+
+  useEffect(() => {
+    if (typeof window === 'undefined') return;
+
+    const mediaQuery = window.matchMedia(MOBILE_BREAKPOINT);
+    const syncIsMobile = (event?: MediaQueryListEvent) => {
+      setIsMobile(event?.matches ?? mediaQuery.matches);
+    };
+
+    syncIsMobile();
+    if (typeof mediaQuery.addEventListener === 'function') {
+      mediaQuery.addEventListener('change', syncIsMobile);
+      return () => mediaQuery.removeEventListener('change', syncIsMobile);
+    }
+
+    mediaQuery.addListener(syncIsMobile);
+    return () => mediaQuery.removeListener(syncIsMobile);
+  }, []);
 
   let content: React.ReactNode;
   if (!ex) {
@@ -86,14 +107,16 @@ export default function InputPanel({ showToolkit = true }: { showToolkit?: boole
           {state.inputProgress && (
             <span className="input-panel-progress">{state.inputProgress}</span>
           )}
-          <button
-            type="button"
-            className="input-panel-action"
-            aria-expanded={!collapsed}
-            onClick={() => setCollapsed((prev) => !prev)}
-          >
-            {collapsed ? 'Expand' : 'Minimize'}
-          </button>
+          {isMobile && (
+            <button
+              type="button"
+              className="input-panel-action"
+              aria-expanded={!collapsed}
+              onClick={() => setCollapsed((prev) => !prev)}
+            >
+              {collapsed ? 'Expand' : 'Minimize'}
+            </button>
+          )}
         </div>
       </div>
       {!collapsed && (

src/state/ExerciseContext.tsx

@@ -3,7 +3,7 @@
 import React, { createContext, useContext, useReducer, useRef, useEffect } from 'react';
 import { AppState, Action } from './types';
 import { reducer, createInitialState } from './reducer';
-import { saveProgress } from './persistence';
+import { loadProgress, saveProgress } from './persistence';
 import { StackSim } from '@/engine/simulators/StackSim';
 import { HeapSim } from '@/engine/simulators/HeapSim';
 import { WinHeapSim } from '@/engine/simulators/WinHeapSim';
@@ -35,6 +35,10 @@ export function ExerciseContextProvider({ children }: { children: React.ReactNod
     ? getExercise(state.currentExerciseId) ?? null
     : null;
 
+  useEffect(() => {
+    dispatch({ type: 'HYDRATE_COMPLETED', completed: loadProgress() });
+  }, []);
+
   // Persist completed exercises whenever they change
   const completedRef = useRef(state.completed);
   useEffect(() => {

src/state/reducer.ts

@@ -1,11 +1,10 @@
 import { AppState, Action } from './types';
 import { BASE_SYMBOLS } from '@/exercises/shared/symbols';
-import { loadProgress } from './persistence';
 
 export function createInitialState(): AppState {
   return {
     currentExerciseId: null,
-    completed: loadProgress(),
+    completed: new Set(),
     logMessages: [],
     inputMode: 'text',
     inputProgress: null,
@@ -34,6 +33,9 @@ export function createInitialState(): AppState {
 
 export function reducer(state: AppState, action: Action): AppState {
   switch (action.type) {
+    case 'HYDRATE_COMPLETED':
+      return { ...state, completed: new Set(action.completed) };
+
     case 'LOAD_EXERCISE':
       return {
         ...state,

src/state/types.ts

@@ -27,6 +27,7 @@ export interface AppState {
 }
 
 export type Action =
+  | { type: 'HYDRATE_COMPLETED'; completed: Set<string> }
   | { type: 'LOAD_EXERCISE'; exerciseId: string }
   | { type: 'LOG'; cls: string; msg: string }
   | { type: 'LOG_BATCH'; messages: Array<{ cls: string; msg: string }> }