Maze generator & solver · minimax-m3

Let me start by exploring the current directory and then building the maze generator and solver visualization.

I need to create a maze generator/solver visualization. The directory is empty besides a `.home` directory. Let me build this.

Requirements:
- 25x15 maze, recursive backtracking
- Start: upper-left, Finish: lower-right
- Animate carving
- BFS or A* for solving, animate exploration
- Highlight complete path
- New Maze and Replay Solver buttons
- Legend
- All inline (CSS/JS)
- No external resources

Let me plan the design:

**Canvas size:** 25x15 cells. Let's use 24px cells = 600x360 canvas. That fits well in 1200x800 viewport.

**Data structure:**
- Each cell has 4 walls (top, right, bottom, left)
- Walls indexed: N=0, E=1, S=2, W=3
- Walls array: walls[col][row][4] = true (present)
- Cell (col, row)

**Recursive Backtracking:**
- Start at (0,0), mark visited
- Pick random unvisited neighbor
- If neighbor exists: remove wall between, push to stack, recurse
- Else: pop stack, backtrack
- Animatable: process one step at a time with requestAnimationFrame

**Generation animation:**
- Carve step by step
- Show current cell highlighted, visited cells colored
- Walls drawn between cells

**Solver (A*):**
- Open set, closed set
- Heuristic: Manhattan distance
- Neighbors: only through open passages (no wall)
- g, h, f scores
- Animate exploration: cells light up as visited
- After done, reconstruct path

**Visual styles:**
- Background: dark
- Walls: white/light
- Visited (during generation): light blue
- Current (during generation): yellow
- Start: green
- Finish: red
- Frontier (open set): orange
- Explored (closed set): blue/dark
- Solution path: gold/yellow

Let me write the code:

```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Maze Generator & Solver</title>
<style>
  body { 
    margin: 0; 
    padding: 20px; 
    background: #1a1a2e; 
    color: #eee; 
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: 100vh;
  }
  h1 { 
    margin: 0 0 16px; 
    font-weight: 500;
    font-size: 22px;
  }
  .controls {
    display: flex;
    gap: 12px;
    margin-bottom: 16px;
  }
  button {
    padding: 8px 16px;
    font-size: 14px;
    background: #4a4e69;
    color: #eee;
    border: 1px solid #6c6f7d;
    border-radius: 4px;
    cursor: pointer;
    transition: background 0.15s;
  }
  button:hover:not(:disabled) {
    background: #6c6f7d;
  }
  button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
  }
  canvas {
    border: 2px solid #6c6f7d;
    background: #22223b;
    image-rendering: pixelated;
  }
  .legend {
    margin-top: 16px;
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
    font-size: 13px;
  }
  .legend-item {
    display: flex;
    align-items: center;
    gap: 6px;
  }
  .swatch {
    width: 16px;
    height: 16px;
    border: 1px solid #555;
  }
  .status {
    margin-top: 8px;
    font-size: 13px;
    color: #aaa;
  }
</style>
</head>
<body>
  <h1>Maze Generator & Solver</h1>
  <div class="controls">
    <button id="newMaze">New Maze</button>
    <button id="replaySolver">Replay Solver</button>
  </div>
  <canvas id="canvas" width="600" height="360"></canvas>
  <div class="legend">
    <div class="legend-item"><div class="swatch" style="background:#4caf50"></div>Start</div>
    <div class="legend-item"><div class="swatch" style="background:#f44336"></div>Finish</div>
    <div class="legend-item"><div class="swatch" style="background:#7e57c2"></div>Visited (gen)</div>
    <div class="legend-item"><div class="swatch" style="background:#fff176"></div>Current (gen)</div>
    <div class="legend-item"><div class="swatch" style="background:#ff9800"></div>Frontier</div>
    <div class="legend-item"><div class="swatch" style="background:#26a69a"></div>Explored</div>
    <div class="legend-item"><div class="swatch" style="background:#ffeb3b"></div>Path</div>
  </div>
  <div class="status" id="status">Ready.</div>

<script>
(() => {
  const COLS = 25;
  const ROWS = 15;
  const CELL = 24;
  const canvas = document.getElementById('canvas');
  const ctx = canvas.getContext('2d');
  canvas.width = COLS * CELL;
  canvas.height = ROWS * CELL;
  
  // Wall directions: 0=N, 1=E, 2=S, 3=W
  const N = 0, E = 1, S = 2, W = 3;
  const DX = [0, 1, 0, -1];
  const DY = [-1, 0, 1, 0];
  const OPP = [S, W, N, E];
  
  let walls;     // walls[x][y][4]
  let visited;   // visited[x][y]
  let genStack;  // stack for backtracking
  let genState;  // 'idle'|'running'|'done'
  let genCurrent; // (x,y) being processed
  let genAnimReq;
  
  let solverOpenSet;
  let solverClosedSet;
  let solverParents;
  let solverG;
  let solverF;
  let solverDone;
  let solverPath;
  let solverState; // 'idle'|'running'|'done'
  let solverAnimReq;
  
  let animCancel = false;
  
  function initWalls() {
    walls = [];
    visited = [];
    for (let x = 0; x < COLS; x++) {
      walls.push([]);
      visited.push([]);
      for (let y = 0; y < ROWS; y++) {
        walls[x].push([true, true, true, true]);
        visited[x].push(false);
      }
    }
  }
  
  function neighbors(x, y) {
    const n = [];
    for (let d = 0; d < 4; d++) {
      const nx = x + DX[d];
      const ny = y + DY[d];
      if (nx >= 0 && nx < COLS && ny >= 0 && ny < ROWS) {
        n.push({x: nx, y: ny, d: d});
      }
    }
    return n;
  }
  
  function shuffle(arr) {
    for (let i = arr.length - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      [arr[i], arr[j]] = [arr[j], arr[i]];
    }
    return arr;
  }
  
  function startGeneration() {
    cancelAnimation();
    initWalls();
    genStack = [{x: 0, y: 0}];
    visited[0][0] = true;
    genCurrent = {x: 0, y: 0};
    genState = 'running';
    solverState = 'idle';
    solverDone = false;
    solverPath = null;
    updateStatus('Generating maze...');
    scheduleDraw();
    scheduleGenStep();
  }
  
  function scheduleGenStep() {
    // Run several steps per frame to control speed
    setTimeout(() => {
      if (genState !== 'running') return;
      const stepsPerTick = 2;
      for (let i = 0; i < stepsPerTick; i++) {
        genStep();
        if (genState !== 'running') break;
      }
      scheduleDraw();
      if (genState === 'running') {
        scheduleGenStep();
      } else {
        updateStatus('Maze complete. Ready to solve.');
      }
    }, 16);
  }
  
  function genStep() {
    if (genStack.length === 0) {
      genState = 'done';
      genCurrent = null;
      return;
    }
    const cur = genStack[genStack.length - 1];
    genCurrent = cur;
    const ns = shuffle(neighbors(cur.x, cur.y));
    let found = false;
    for (const n of ns) {
      if (!visited[n.x][n.y]) {
        // Carve wall
        walls[cur.x][cur.y][n.d] = false;
        walls[n.x][n.y][OPP[n.d]] = false;
        visited[n.x][n.y] = true;
        genStack.push({x: n.x, y: n.y});
        found = true;
        break;
      }
    }
    if (!found) {
      genStack.pop();
    }
  }
  
  // A* solver
  function startSolver() {
    if (genState !== 'done') return;
    if (solverState === 'running') return;
    cancelSolverAnimation();
    solverOpenSet = [{x: 0, y: 0}];
    solverClosedSet = new Set();
    solverParents = {};
    solverG = {};
    solverF = {};
    solverG['0,0'] = 0;
    solverF['0,0'] = manhattan(0, 0, COLS - 1, ROWS - 1);
    solverDone = false;
    solverPath = null;
    solverState = 'running';
    updateStatus('Solving with A*...');
    scheduleDraw();
    scheduleSolverStep();
  }
  
  function manhattan(x1, y1, x2, y2) {
    return Math.abs(x1 - x2) + Math.abs(y1 - y2);
  }
  
  function getOpenNeighbors(x, y) {
    // neighbors reachable through open passages
    const ns = [];
    for (let d = 0; d < 4; d++) {
      if (walls[x][y][d]) continue;
      const nx = x + DX[d];
      const ny = y + DY[d];
      if (nx >= 0 && nx < COLS && ny >= 0 && ny < ROWS) {
        ns.push({x: nx, y: ny, d: d});
      }
    }
    return ns;
  }
  
  function scheduleSolverStep() {
    setTimeout(() => {
      if (solverState !== 'running') return;
      // Process a few steps per tick
      const stepsPerTick = 3;
      for (let i = 0; i < stepsPerTick; i++) {
        solverStep();
        if (solverState !== 'running') break;
      }
      scheduleDraw();
      if (solverState === 'running') {
        scheduleSolverStep();
      }
    }, 16);
  }
  
  function solverStep() {
    if (solverOpenSet.length === 0) {
      solverState = 'done';
      return;
    }
    // Find lowest f
    let bestIdx = 0;
    for (let i = 1; i < solverOpenSet.length; i++) {
      const a = solverF[solverOpenSet[i].x + ',' + solverOpenSet[i].y];
      const b = solverF[solverOpenSet[bestIdx].x + ',' + solverOpenSet[bestIdx].y];
      if (a < b) bestIdx = i;
    }
    const cur = solverOpenSet[bestIdx];
    if (cur.x === COLS - 1 && cur.y === ROWS - 1) {
      // Reconstruct path
      const path = [];
      let p = cur;
      while (p) {
        path.push(p);
        p = solverParents[p.x + ',' + p.y];
      }
      solverPath = path.reverse();
      solverState = 'done';
      updateStatus('Solution found! Path length: ' + solverPath.length);
      return;
    }
    solverOpenSet.splice(bestIdx, 1);
    solverClosedSet.add(cur.x + ',' + cur.y);
    for (const n of getOpenNeighbors(cur.x, cur.y)) {
      const key = n.x + ',' + n.y;
      if (solverClosedSet.has(key)) continue;
      const tentativeG = solverG[cur.x + ',' + cur.y] + 1;
      const inOpen = solverOpenSet.some(o => o.x === n.x && o.y === n.y);
      if (!inOpen || tentativeG < solverG[key]) {
        solverParents[key] = cur;
        solverG[key] = tentativeG;
        solverF[key] = tentativeG + manhattan(n.x, n.y, COLS - 1, ROWS - 1);
        if (!inOpen) {
          solverOpenSet.push(n);
        }
      }
    }
  }
  
  function cancelAnimation() {
    genState = 'idle';
    solverState = 'idle';
    genStack = null;
  }
  
  function cancelSolverAnimation() {
    solverState = 'idle';
  }
  
  function draw() {
    // Background
    ctx.fillStyle = '#22223b';
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    
    // Cells (visiting color during generation)
    if (genState === 'running' && genCurrent) {
      // ...
    }
    
    // Visited cells color
    for (let x = 0; x < COLS; x++) {
      for (let y = 0; y < ROWS; y++) {
        if (visited[x][y] && genState !== 'done') {
          ctx.fillStyle = '#3a3a5c';
          ctx.fillRect(x * CELL + 1, y * CELL + 1, CELL - 2, CELL - 2);
        }
      }
    }
    
    // Solver overlay
    if (solverState === 'running' || solverState === 'done') {
      // Explored
      for (const key of solverClosedSet) {
        const [x, y] = key.split(',').map(Number);
        ctx.fillStyle = '#26a69a';
        ctx.fillRect(x * CELL + 2, y * CELL + 2, CELL - 4, CELL - 4);
      }
      // Frontier
      for (const n of solverOpenSet) {
        ctx.fillStyle = '#ff9800';
        ctx.fillRect(n.x * CELL + 2, n.y * CELL + 2, CELL - 4, CELL - 4);
      }
      // Path
      if (solverPath) {
        for (const p of solverPath) {
          ctx.fillStyle = '#ffeb3b';
          ctx.fillRect(p.x * CELL + 2, p.y * CELL + 2, CELL - 4, CELL - 4);
        }
      }
    }
    
    // Current cell during gen
    if (genState === 'running' && genCurrent) {
      ctx.fillStyle = '#fff176';
      ctx.fillRect(genCurrent.x * CELL + 2, genCurrent.y * CELL + 2, CELL - 4, CELL - 4);
    }
    
    // Start / Finish
    ctx.fillStyle = '#4caf50';
    ctx.fillRect(0 * CELL + 4, 0 * CELL + 4, CELL - 8, CELL - 8);
    ctx.fillStyle = '#f44336';
    ctx.fillRect((COLS-1) * CELL + 4, (ROWS-1) * CELL + 4, CELL - 8, CELL - 8);
    
    // Walls
    ctx.strokeStyle = '#e0e0e0';
    ctx.lineWidth = 2;
    ctx.lineCap = 'square';
    for (let x = 0; x < COLS; x++) {
      for (let y = 0; y < ROWS; y++) {
        if (walls[x][y][N]) {
          ctx.beginPath();
          ctx.moveTo(x * CELL, y * CELL);
          ctx.lineTo((x + 1) * CELL, y * CELL);
          ctx.stroke();
        }
        if (walls[x][y][W]) {
          ctx.beginPath();
          ctx.moveTo(x * CELL, y * CELL);
          ctx.lineTo(x * CELL, (y + 1) * CELL);
          ctx.stroke();
        }
        // Only draw E wall if at rightmost column or cell to right doesn't have W removed
        if (x === COLS - 1 && walls[x][y][E]) {
          ctx.beginPath();
          ctx.moveTo((x + 1) * CELL, y * CELL);
          ctx.lineTo((x + 1) * CELL, (y + 1) * CELL);
          ctx.stroke();
        }
        if (y === ROWS - 1 && walls[x][y][S]) {
          ctx.beginPath();
          ctx.moveTo(x * CELL, (y + 1) * CELL);
          ctx.lineTo((x + 1) * CELL, (y + 1) * CELL);
          ctx.stroke();
        }
      }
    }
  }
  
  let drawScheduled = false;
  function scheduleDraw() {
    if (drawScheduled) return;
    drawScheduled = true;
    requestAnimationFrame(() => {
      drawScheduled = false;
      draw();
    });
  }
  
  function updateStatus(msg) {
    document.getElementById('status').textContent = msg;
  }
  
  document.getElementById('newMaze').addEventListener('click', () => {
    startGeneration();
  });
  document.getElementById('replaySolver').addEventListener('click', () => {
    if (genState === 'done') {
      startSolver();
    } else {
      updateStatus('Wait for maze generation to finish.');
    }
  });
  
  // Initial maze
  startGeneration();
  
  // Auto-solve after generation completes
  function checkAutoSolve() {
    if (genState === 'done' && solverState === 'idle' && !solverDone) {
      startSolver();
    } else {
      setTimeout(checkAutoSolve, 100);
    }
  }
  setTimeout(checkAutoSolve, 200);
})();
</script>
</body>
</html>
```

Wait, I should think about the issue with `genState = 'idle'` - the test mentioned "request New Maze while animation is active. Check that the new generation replaces the previous view cleanly." So I need to make sure New Maze cancels any ongoing animation properly.

Let me also reconsider the auto-solve behavior. Actually, the task doesn't say to auto-solve. It just says to animate the solver after generation finishes. Let me make it auto-solve after a brief delay, so the user sees the full flow. But also a "Replay Solver" button. Yes, auto-solve makes sense - it shows the complete demo cycle.

Actually, looking again: "After generation finishes, animate either BFS or A-star exploring the maze". So yes, auto-solve after generation is correct.

Let me also reconsider some bugs:
1. In `startGeneration()`, I should clear `solverOpenSet`, `solverClosedSet`, `solverPath` etc.
2. When starting solver, need to make sure genState is done.

Let me also think about how the recursive backtracking animation should look. The way I'm doing it now, each step either carves a new cell or pops the stack. With 2 steps per tick, that's pretty fast for a 25x15 maze (375 cells). Total: ~375/2 = ~190 ticks * 16ms = ~3 seconds. That feels right.

For A* with 3 steps per tick, total steps could be up to ~375, so ~125 ticks = ~2 seconds. Reasonable.

Let me clean up and rewrite the code:

Actually wait, I should think about the structure better. Let me use proper functions and clean up state management.

Let me also add a "fill" style to make visited cells visible during generation - a slight tint. And make current cell stand out.

Also, for the start cell, it's also "visited" during generation, so it might show the green start marker over the visited color. Let me layer draws properly: visited first, then current highlight, then start/finish on top.

Actually, my current draw order seems OK but let me think:
1. Background
2. Visited cells (during gen) - tint of background
3. Explored cells (solver) - teal
4. Frontier cells (solver) - orange  
5. Path cells (solver done) - yellow
6. Current gen cell - bright yellow
7. Start/finish markers
8. Walls on top

Hmm, start/finish are part of visited/explored too. Let me layer:
1. Background
2. Visited cells (during gen)
3. Solver explored cells
4. Solver frontier
5. Solver path
6. Current gen cell
7. Start/finish markers
8. Walls

Walls last so they're always crisp.

Let me refine:

```javascript
function draw() {
  ctx.fillStyle = '#22223b';
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  
  // Visited cells during generation
  if (genState === 'running' && genCurrent) {
    for (let x = 0; x < COLS; x++) {
      for (let y = 0; y < ROWS; y++) {
        if (visited[x][y]) {
          ctx.fillStyle = '#3a3a5c';
          ctx.fillRect(x * CELL + 1, y * CELL + 1, CELL - 2, CELL - 2);
        }
      }
    }
  }
  
  // Explored cells
  if (solverClosedSet) {
    for (const key of solverClosedSet) {
      const [x, y] = key.split(',').map(Number);
      ctx.fillStyle = '#26a69a';
      ctx.fillRect(x * CELL + 2, y * CELL + 2, CELL - 4, CELL - 4);
    }
  }
  
  // Frontier
  if (solverOpenSet) {
    for (const n of solverOpenSet) {
      ctx.fillStyle = '#ff9800';
      ctx.fillRect(n.x * CELL + 2, n.y * CELL + 2, CELL - 4, CELL - 4);
    }
  }
  
  // Path
  if (solverPath) {
    for (const p of solverPath) {
      ctx.fillStyle = '#ffeb3b';
      ctx.fillRect(p.x * CELL + 3, p.y * CELL + 3, CELL - 6, CELL - 6);
    }
  }
  
  // Current gen cell
  if (genState === 'running' && genCurrent) {
    ctx.fillStyle = '#fff176';
    ctx.fillRect(genCurrent.x * CELL + 2, genCurrent.y * CELL + 2, CELL - 4, CELL - 4);
  }
  
  // Start marker
  ctx.fillStyle = '#4caf50';
  ctx.fillRect(2, 2, CELL - 4, CELL - 4);
  
  // Finish marker
  ctx.fillStyle = '#f44336';
  ctx.fillRect((COLS - 1) * CELL + 2, (ROWS - 1) * CELL + 2, CELL - 4, CELL - 4);
  
  // Walls
  drawWalls();
}
```

For walls, I need to draw each wall once (not both sides). The trick is:
- N wall of (x,y) is the same as S wall of (x,y-1)
- W wall of (x,y) is the same as E wall of (x-1,y)

So I'll only draw N and W walls for each cell. The boundary walls (S of bottom row, E of rightmost col) need to be drawn separately.

```javascript
function drawWalls() {
  ctx.strokeStyle = '#e0e0e0';
  ctx.lineWidth = 2;
  ctx.beginPath();
  for (let x = 0; x < COLS; x++) {
    for (let y = 0; y < ROWS; y++) {
      const px = x * CELL, py = y * CELL;
      if (walls[x][y][N]) {
        ctx.moveTo(px, py);
        ctx.lineTo(px + CELL, py);
      }
      if (walls[x][y][W]) {
        ctx.moveTo(px, py);
        ctx.lineTo(px, py + CELL);
      }
      if (y === ROWS - 1 && walls[x][y][S]) {
        ctx.moveTo(px, py + CELL);
        ctx.lineTo(px + CELL, py + CELL);
      }
      if (x === COLS - 1 && walls[x][y][E]) {
        ctx.moveTo(px + CELL, py);
        ctx.lineTo(px + CELL, py + CELL);
      }
    }
  }
  ctx.stroke();
}
```

Actually, I think this might leave a gap on cell boundaries where one cell has the wall and the adjacent cell doesn't (or rather, both should agree). Since I always set both sides when carving, they should agree. Let me verify:
- When carving from (x,y) to (nx,ny) through direction d:
  - walls[x][y][d] = false
  - walls[nx][ny][OPP[d]] = false

Yes, both sides are cleared, so they'll always agree. Good.

Now let me also think about the auto-solve. After generation finishes, I want to automatically start the solver. The user can interrupt with New Maze at any time.

Let me write the code properly. I'll use `setInterval` or recursion with `setTimeout` for animation.

Actually, instead of using `setTimeout` chains which can be hard to cancel, let me use a single `requestAnimationFrame` loop that runs all steps. This makes cancellation cleaner.

```javascript
let rafId = null;

function loop() {
  rafId = null;
  if (genState === 'running') {
    const stepsPerTick = 2;
    for (let i = 0; i < stepsPerTick; i++) {
      genStep();
      if (genState !== 'running') break;
    }
  } else if (solverState === 'running') {
    const stepsPerTick = 3;
    for (let i = 0; i < stepsPerTick; i++) {
      solverStep();
      if (solverState !== 'running') break;
    }
  }
  draw();
  if (genState === 'running' || solverState === 'running') {
    rafId = requestAnimationFrame(loop);
  } else {
    // check transitions
    if (genState === 'done' && solverState === 'idle') {
      // start solver automatically
      startSolver();
      rafId = requestAnimationFrame(loop);
    }
  }
}
```

Hmm, but this couples generation and solver timing. Let me separate them. Actually, the simplest is to use a single loop that progresses whichever state is active. Let me think...

Actually, since both gen and solver use the same loop pattern, let me use a generic "tick" function that runs the current state's step.

Let me use this approach:

```javascript
function tick() {
  if (genState === 'running') {
    // gen steps
    for (let i = 0; i < 2; i++) {
      if (genState !== 'running') break;
      genStep();
    }
  } else if (solverState === 'running') {
    for (let i = 0; i < 3; i++) {
      if (solverState !== 'running') break;
      solverStep();
    }
  }
  draw();
  if (genState === 'running' || solverState === 'running') {
    rafId = requestAnimationFrame(tick);
  } else if (genState === 'done' && solverState === 'idle' && autoSolve) {
    startSolver();
    rafId = requestAnimationFrame(tick);
  }
}

function startLoop() {
  if (rafId) return;
  rafId = requestAnimationFrame(tick);
}

function stopLoop() {
  if (rafId) {
    cancelAnimationFrame(rafId);
    rafId = null;
  }
}
```

Wait, there's a subtle issue. When gen finishes and we auto-solve, that's fine. But when user clicks New Maze during solver animation, we should cancel the solver cleanly.

Let me make sure: `cancelAnimation()` sets both genState and solverState to 'idle', and clears relevant state. Then `startGeneration()` reinitializes everything.

OK let me write this out properly:

```javascript
function cancelAnimation() {
  genState = 'idle';
  solverState = 'idle';
  genStack = null;
  genCurrent = null;
  solverOpenSet = null;
  solverClosedSet = null;
  solverPath = null;
}
```

After cancel, when `startGeneration()` is called, it sets up fresh state. Good.

Let me put together the complete code now. I'll be careful about edge cases.

One more consideration: the test mentions "If the solver starts during inspection, check that its visible steps follow open passages." So the solver must only step through cells connected by open passages. My `getOpenNeighbors` function does this by checking `walls[x][y][d]` for each direction.

Wait, but during the auto-solve transition, there's a brief moment where genState is 'done' but solverState is 'idle'. Then `startSolver()` is called which sets solverState to 'running'. The check in the loop should work.

Let me also think: do I need to handle when the user clicks Replay Solver during generation? The button should be disabled, or just no-op. Let me disable it during generation.

Actually I'll just have it check genState and ignore the click if not done.

Let me also add a small visual indicator for start/finish - maybe a triangle or letter "S"/"F"? Or just a colored square is enough. The legend explains.

Let me write the final code:

```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Maze Generator & Solver</title>
<style>
  * { box-sizing: border-box; }
  body {
    margin: 0;
    padding: 20px;
    background: #1a1a2e;
    color: #eaeaea;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: 100vh;
  }
  h1 {
    margin: 0 0 12px;
    font-size: 22px;
    font-weight: 500;
    letter-spacing: 0.5px;
  }
  .subtitle {
    margin: 0 0 16px;
    font-size: 13px;
    color: #999;
  }
  .controls {
    display: flex;
    gap: 10px;
    margin-bottom: 16px;
  }
  button {
    padding: 8px 18px;
    font-size: 14px;
    background: #4a4e69;
    color: #eaeaea;
    border: 1px solid #6c6f7d;
    border-radius: 4px;
    cursor: pointer;
    transition: background 0.15s;
    font-family: inherit;
  }
  button:hover { background: #6c6f7d; }
  button:active { background: #5a5e79; }
  canvas {
    border: 2px solid #6c6f7d;
    background: #22223b;
    display: block;
  }
  .legend {
    margin-top: 16px;
    display: flex;
    flex-wrap: wrap;
    gap: 14px;
    justify-content: center;
    font-size: 13px;
    max-width: 640px;
  }
  .legend-item {
    display: flex;
    align-items: center;
    gap: 6px;
  }
  .swatch {
    width: 16px;
    height: 16px;
    border: 1px solid #444;
    border-radius: 2px;
  }
  .status {
    margin-top: 12px;
    font-size: 13px;
    color: #aaa;
    min-height: 18px;
  }
</style>
</head>
<body>
  <h1>Maze Generator &amp; Solver</h1>
  <div class="subtitle">25 × 15 grid · recursive backtracking · A* search</div>
  <div class="controls">
    <button id="newMaze">New Maze</button>
    <button id="replaySolver">Replay Solver</button>
  </div>
  <canvas id="canvas"></canvas>
  <div class="legend">
    <div class="legend-item"><div class="swatch" style="background:#4caf50"></div>Start</div>
    <div class="legend-item"><div class="swatch" style="background:#f44336"></div>Finish</div>
    <div class="legend-item"><div class="swatch" style="background:#7e57c2"></div>Visited (gen)</div>
    <div class="legend-item"><div class="swatch" style="background:#fff176"></div>Current (gen)</div>
    <div class="legend-item"><div class="swatch" style="background:#ff9800"></div>Frontier</div>
    <div class="legend-item"><div class="swatch" style="background:#26a69a"></div>Explored</div>
    <div class="legend-item"><div class="swatch" style="background:#ffeb3b"></div>Solution path</div>
  </div>
  <div class="status" id="status">Initializing...</div>

<script>
(() => {
  const COLS = 25;
  const ROWS = 15;
  const CELL = 24;
  const canvas = document.getElementById('canvas');
  const ctx = canvas.getContext('2d');
  canvas.width = COLS * CELL;
  canvas.height = ROWS * CELL;
  
  const N = 0, E = 1, S = 2, W = 3;
  const DX = [0, 1, 0, -1];
  const DY = [-1, 0, 1, 0];
  const OPP = [S, W, N, E];
  
  let walls;
  let visited;
  let genStack;
  let genState; // 'idle' | 'running' | 'done'
  let genCurrent;
  
  let solverOpenSet;
  let solverClosedSet;
  let solverParents;
  let solverG;
  let solverF;
  let solverState;
  let solverPath;
  
  let rafId = null;
  let autoSolve = true;
  
  function initWalls() {
    walls = [];
    visited = [];
    for (let x = 0; x < COLS; x++) {
      walls.push([]);
      visited.push([]);
      for (let y = 0; y < ROWS; y++) {
        walls[x].push([true, true, true, true]);
        visited[x].push(false);
      }
    }
  }
  
  function clearAll() {
    initWalls();
    genStack = null;
    genCurrent = null;
    solverOpenSet = null;
    solverClosedSet = null;
    solverParents = null;
    solverG = null;
    solverF = null;
    solverPath = null;
    genState = 'idle';
    solverState = 'idle';
  }
  
  function neighbors(x, y) {
    const result = [];
    for (let d = 0; d < 4; d++) {
      const nx = x + DX[d];
      const ny = y + DY[d];
      if (nx >= 0 && nx < COLS && ny >= 0 && ny < ROWS) {
        result.push({x: nx, y: ny, d: d});
      }
    }
    return result;
  }
  
  function shuffle(arr) {
    for (let i = arr.length - 1; i > 0; i--) {
      const j = Math.floor(Math.random() * (i + 1));
      [arr[i], arr[j]] = [arr[j], arr[i]];
    }
    return arr;
  }
  
  function startGeneration() {
    clearAll();
    genStack = [{x: 0, y: 0}];
    visited[0][0] = true;
    genCurrent = {x: 0, y: 0};
    genState = 'running';
    updateStatus('Generating maze (recursive backtracking)...');
    draw();
    startLoop();
  }
  
  function genStep() {
    if (genStack.length === 0) {
      genState = 'done';
      genCurrent = null;
      return;
    }
    const cur = genStack[genStack.length - 1];
    genCurrent = cur;
    const ns = shuffle(neighbors(cur.x, cur.y));
    let carved = false;
    for (const n of ns) {
      if (!visited[n.x][n.y]) {
        walls[cur.x][cur.y][n.d] = false;
        walls[n.x][n.y][OPP[n.d]] = false;
        visited[n.x][n.y] = true;
        genStack.push({x: n.x, y: n.y});
        carved = true;
        break;
      }
    }
    if (!carved) {
      genStack.pop();
    }
  }
  
  function manhattan(x1, y1, x2, y2) {
    return Math.abs(x1 - x2) + Math.abs(y1 - y2);
  }
  
  function getOpenNeighbors(x, y) {
    const result = [];
    for (let d = 0; d < 4; d++) {
      if (walls[x][y][d]) continue; // wall present, can't go
      const nx = x + DX[d];
      const ny = y + DY[d];
      if (nx >= 0 && nx < COLS && ny >= 0 && ny < ROWS) {
        result.push(nx + ',' + ny);
      }
    }
    return result;
  }
  
  function startSolver() {
    if (genState !== 'done') return;
    solverOpenSet = ['0,0'];
    solverClosedSet = new Set();
    solverParents = {};
    solverG = {'0,0': 0};
    solverF = {'0,0': manhattan(0, 0, COLS - 1, ROWS - 1)};
    solverPath = null;
    solverState = 'running';
    updateStatus('Solving with A* search...');
    draw();
    startLoop();
  }
  
  function solverStep() {
    if (solverOpenSet.length === 0) {
      solverState = 'done';
      updateStatus('No solution found.');
      return;
    }
    // Find node with lowest f in openSet
    let bestIdx = 0;
    for (let i = 1; i < solverOpenSet.length; i++) {
      if (solverF[solverOpenSet[i]] < solverF[solverOpenSet[bestIdx]]) {
        bestIdx = i;
      }
    }
    const currentKey = solverOpenSet[bestIdx];
    const [cx, cy] = currentKey.split(',').map(Number);
    
    if (cx === COLS - 1 && cy === ROWS - 1) {
      // Reconstruct path
      const path = [];
      let k = currentKey;
      while (k) {
        const [x, y] = k.split(',').map(Number);
        path.push({x, y});
        k = solverParents[k];
      }
      solverPath = path;
      solverState = 'done';
      updateStatus('Solution found! Path length: ' + path.length + ' cells.');
      return;
    }
    
    solverOpenSet.splice(bestIdx, 1);
    solverClosedSet.add(currentKey);
    
    const neighbors = getOpenNeighbors(cx, cy);
    for (const nKey of neighbors) {
      if (solverClosedSet.has(nKey)) continue;
      const tentativeG = solverG[currentKey] + 1;
      const inOpen = solverOpenSet.includes(nKey);
      if (!inOpen || tentativeG < (solverG[nKey] ?? Infinity)) {
        const [nx, ny] = nKey.split(',').map(Number);
        solverParents[nKey] = {x: cx, y: cy};
        solverG[nKey] = tentativeG;
        solverF[nKey] = tentativeG + manhattan(nx, ny, COLS - 1, ROWS - 1);
        if (!inOpen) {
          solverOpenSet.push(nKey);
        }
      }
    }
  }
  
  function startLoop() {
    if (rafId !== null) return;
    rafId = requestAnimationFrame(tick);
  }
  
  function stopLoop() {
    if (rafId !== null) {
      cancelAnimationFrame(rafId);
      rafId = null;
    }
  }
  
  function tick() {
    rafId = null;
    if (genState === 'running') {
      for (let i = 0; i < 2 && genState === 'running'; i++) {
        genStep();
      }
    } else if (solverState === 'running') {
      for (let i = 0; i < 3 && solverState === 'running'; i++) {
        solverStep();
      }
    }
    draw();
    if (genState === 'running' || solverState === 'running') {
      rafId = requestAnimationFrame(tick);
    } else if (genState === 'done' && solverState === 'idle' && autoSolve) {
      startSolver();
      rafId = requestAnimationFrame(tick);
    }
  }
  
  function draw() {
    // Background
    ctx.fillStyle = '#22223b';
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    
    // Visited cells during generation (subtle)
    if (genState === 'running') {
      for (let x = 0; x < COLS; x++) {
        for (let y = 0; y < ROWS; y++) {
          if (visited[x][y]) {
            ctx.fillStyle = '#3d3d5e';
            ctx.fillRect(x * CELL + 1, y * CELL + 1, CELL - 2, CELL - 2);
          }
        }
      }
    }
    
    // Explored cells (closed set)
    if (solverClosedSet) {
      for (const key of solverClosedSet) {
        const [x, y] = key.split(',').map(Number);
        ctx.fillStyle = '#26a69a';
        ctx.fillRect(x * CELL + 3, y * CELL + 3, CELL - 6, CELL - 6);
      }
    }
    
    // Frontier (open set)
    if (solverOpenSet) {
      for (const key of solverOpenSet) {
        const [x, y] = key.split(',').map(Number);
        ctx.fillStyle = '#ff9800';
        ctx.fillRect(x * CELL + 3, y * CELL + 3, CELL - 6, CELL - 6);
      }
    }
    
    // Solution path
    if (solverPath) {
      for (const p of solverPath) {
        ctx.fillStyle = '#ffeb3b';
        ctx.fillRect(p.x * CELL + 3, p.y * CELL + 3, CELL - 6, CELL - 6);
      }
    }
    
    // Current gen cell
    if (genState === 'running' && genCurrent) {
      ctx.fillStyle = '#fff176';
      ctx.fillRect(genCurrent.x * CELL + 2, genCurrent.y * CELL + 2, CELL - 4, CELL - 4);
    }
    
    // Start marker (top-left)
    ctx.fillStyle = '#4caf50';
    ctx.fillRect(3, 3, CELL - 6, CELL - 6);
    
    // Finish marker (bottom-right)
    ctx.fillStyle = '#f44336';
    ctx.fillRect((COLS - 1) * CELL + 3, (ROWS - 1) * CELL + 3, CELL - 6, CELL - 6);
    
    // Walls
    drawWalls();
  }
  
  function drawWalls() {
    ctx.strokeStyle = '#e0e0e0';
    ctx.lineWidth = 2;
    ctx.lineCap = 'square';
    ctx.beginPath();
    for (let x = 0; x < COLS; x++) {
      for (let y = 0; y < ROWS; y++) {
        const px = x * CELL;
        const py = y * CELL;
        if (walls[x][y][N]) {
          ctx.moveTo(px, py);
          ctx.lineTo(px + CELL, py);
        }
        if (walls[x][y][W]) {
          ctx.moveTo(px, py);
          ctx.lineTo(px, py + CELL);
        }
        if (y === ROWS - 1 && walls[x][y][S]) {
          ctx.moveTo(px, py + CELL);
          ctx.lineTo(px + CELL, py + CELL);
        }
        if (x === COLS - 1 && walls[x][y][E]) {
          ctx.moveTo(px + CELL, py);
          ctx.lineTo(px + CELL, py + CELL);
        }
      }
    }
    ctx.stroke();
  }
  
  function updateStatus(msg) {
    document.getElementById('status').textContent = msg;
  }
  
  document.getElementById('newMaze').addEventListener('click', () => {
    autoSolve = true;
    startGeneration();
  });
  
  document.getElementById('replaySolver').addEventListener('click', () => {
    if (genState !== 'done') {
      updateStatus('Wait for maze generation to finish.');
      return;
    }
    autoSolve = false;
    startSolver();
  });
  
  // Boot
  startGeneration();
})();
</script>
</body>
</html>
```

Wait, I notice that `clearAll` calls `initWalls`, which means `walls` becomes a fresh object. But `genStep` references `walls[cur.x][cur.y]` etc. That should work.

Let me also check `manhattan` import... it's defined after the IIFE body uses it via `startSolver()`. But `startSolver` is only called via event handler or at boot, so by the time it's called, `manhattan` is defined. Function declarations are hoisted, so even if I called it at the top, it'd work. Good.

Actually wait, in my code I have `function manhattan(...)` which is a function declaration. These are hoisted. So no issue.

Let me check one bug: when `solverStep` reconstructs the path, I do `solverParents[k]` which returns `{x, y}` object. Then I assign `k = solverParents[k]` which is the object. Then I do `k.split(',')` which fails!

Yes, that's a bug. Let me fix it: use key strings consistently.

```javascript
const path = [];
let k = currentKey;
while (k) {
  const [x, y] = k.split(',').map(Number);
  path.push({x, y});
  k = solverParents[k]; // this is a key string or undefined
}
```

But I set `solverParents[nKey] = {x: cx, y: cy};` which is an object, not a key. Let me fix:

```javascript
solverParents[nKey] = currentKey;
```

Then `solverParents[k]` returns the parent key (string). Good.

Let me also verify: `solverG[nKey]` - if nKey is not in solverG, returns undefined. I check `(solverG[nKey] ?? Infinity)`. Good.

Hmm, actually `(solverG[nKey] ?? Infinity)` - the `??` operator works for null/undefined. `undefined ?? Infinity` returns Infinity. Good.

But wait, `solverG[nKey]` returns undefined if not set. Then `tentativeG < undefined` is false. But the `?? Infinity` won't help because we're checking `tentativeG < (solverG[nKey] ?? Infinity)`. If `solverG[nKey]` is undefined, this becomes `tentativeG < Infinity` which is true (assuming tentativeG is finite). So the condition `!inOpen || tentativeG < solverG[nKey]` with the `??` form should be OK.

Actually let me simplify:
```javascript
if (!inOpen) {
  // always add
  solverParents[nKey] = currentKey;
  solverG[nKey] = tentativeG;
  solverF[nKey] = tentativeG + h;
  solverOpenSet.push(nKey);
} else if (tentativeG < solverG[nKey]) {
  // found better path
  solverParents[nKey] = currentKey;
  solverG[nKey] = tentativeG;
  solverF[nKey] = tentativeG + h;
}
```

Cleaner. Let me use that.

Also, let me think about edge case: what if `nKey === currentKey`? That can't happen because we only get neighbors of cells, not the cell itself. Good.

OK let me also double-check the wall drawing. When I carve from (0,0) to (0,1) via S direction (d=2):
- walls[0][0][2] = false (S of top-left)
- walls[0][1][0] = false (N of below)

In drawWalls:
- For (0,0): N and W drawn (if true). S not drawn here (we only draw S for y===ROWS-1). E not drawn here.
- For (0,1): N not drawn (was carved). W drawn if true.

So the wall between (0,0) and (0,1) is removed correctly.

But what about the outer boundary? When y=0, N is outer boundary. walls[x][0][0] starts as true. Not carved. Drawn. Good.

When x=0, W is outer boundary. walls[0][y][3] starts as true. Not carved. Drawn. Good.

When y=ROWS-1, S is outer boundary. walls[x][ROWS-1][2] starts as true. The draw code checks `y === ROWS - 1 && walls[x][y][S]`. Good.

When x=COLS-1, E is outer boundary. walls[COLS-1][y][1] starts as true. The draw code checks `x === COLS - 1 && walls[x][y][E]`. Good.

Looks correct.

Let me also think about the visual: with CELL=24, the cell rectangles will be 24x24. Walls drawn at integer pixel boundaries, lineWidth 2. With pixel-aligned lines and width 2, this should look crisp at 1200x800 viewport.

Let me write the final HTML and test it.

One more thing - the auto-solve after generation. When `genState` becomes 'done' and `solverState` is 'idle' and `autoSolve`, then `startSolver()` is called. But `startSolver()` calls `startLoop()` which is gated by `if (rafId !== null) return;`. At this point in `tick()`, after the gen finishes, we set rafId = null at the start of tick. Wait no - we set `rafId = null` at start of tick, then in this frame we update states. At end, we check conditions. If we should run, we set rafId = requestAnimationFrame(tick). But if we're in the case where gen just finished and we want to start solver, we call startSolver() then request raf. startSolver calls startLoop which checks rafId. rafId was set by the line `rafId = requestAnimationFrame(tick)` at end of tick. So startLoop will see rafId !== null and skip.

Hmm that's a bug. Let me fix the flow:

```javascript
function tick() {
  if (rafId !== null) rafId = null;
  // ... do steps ...
  draw();
  if (genState === 'running' || solverState === 'running') {
    rafId = requestAnimationFrame(tick);
  } else if (genState === 'done' && solverState === 'idle' && autoSolve) {
    startSolver(); // this calls startLoop which sets rafId
    if (rafId === null) rafId = requestAnimationFrame(tick); // fallback
  }
}
```

Actually let me restructure. The `startLoop` guard is meant to prevent multiple loops. Let me make it simpler - just set rafId directly:

```javascript
function scheduleTick() {
  rafId = requestAnimationFrame(tick);
}
```

And remove startLoop. Then tick just keeps rescheduling itself.

```javascript
function tick() {
  rafId = null;
  // do steps
  if (genState === 'running' || solverState === 'running') {
    rafId = requestAnimationFrame(tick);
  } else if (genState === 'done' && solverState === 'idle' && autoSolve) {
    startSolver();
    rafId = requestAnimationFrame(tick);
  }
}
```

And when starting gen/solver, set rafId directly.

Let me clean this up. I'll write it now and test.

Actually let me also reconsider: do I want to animate step by step? Or do I want a smoother experience? With 2 gen steps per frame at 60fps, that's 120 steps/sec. For a 25x15 = 375 cell maze, generation takes ~3 seconds. That feels good.

For A*, with 3 steps per frame, 180 steps/sec. A 25x15 maze has ~375 cells, and A* typically explores most of them. So ~2 seconds. Good.

Let me finalize the code.

Actually, one more thing: the visualization should be "frame-by-frame" progressive. With requestAnimationFrame running at ~60fps and 2-3 steps per frame, the visualization should look smooth.

Let me write the final HTML:

The directory is empty. Let me write the index.html with the maze generator and solver visualization.

Now let me run the file in the browser and inspect the initial output.

The maze generation has started. I can see:
- Green start at top-left
- Red finish at bottom-right
- Most cells still have all 4 walls (uncarved)
- Yellow current cell and purple visited cells are showing the carving progress at the top-left
- Status: "Generating maze (recursive backtracking)..."

Let me wait for the generation to progress and capture more frames.

The maze is being generated. The visited cells (purple) are filling in as the algorithm carves through them. The yellow current cell is moving around. I can see the maze is taking shape. Let me wait for it to complete and start solving.

Let me check if generation is done.

Wait, this is wrong! The solver is showing a LOT of exploration and solution path cells all over the place, but the maze walls don't look complete. There are large areas of the canvas that show no walls. Let me look more carefully...

Actually, looking at the screenshot:
- The teal "Explored" cells and yellow "Path" cells fill most of the maze area
- The dark cells (no walls) form a large connected region in the upper-right
- The orange "Frontier" cells are scattered

Wait, I think the issue is the wall drawing. Look at the top-right area - there's a region with no walls visible at all. That's not right. Every cell should have walls drawn around it (between it and its neighbors) - even if its neighbors are explored, the walls should still be there.

Hmm, actually let me re-examine. Looking again at the screenshot:
- The teal/yellow cells cover the left and bottom portions - those have walls visible
- The dark area in the upper-right - those cells are mostly unexplored (not in closed or open set)?

Wait, but A* explores all reachable cells. The dark cells in the upper-right are likely cells that haven't been processed yet because the animation is fast and the screenshot caught it mid-search? But it says "Solution found!" - the path is complete.

Hmm, this is strange. Let me look again...

Oh wait! Looking more carefully at the screenshot:
- The "dark" cells in the upper-right have NO walls drawn. That's the issue.
- Actually wait, I think those cells DO have walls - the dark color is just the background showing through. But it doesn't look right because the cells are uncolored.

Wait, let me think again. The image shows:
- Top-left: green start cell
- Bottom-right: red finish cell
- Most of left/bottom: teal/yellow explored/path cells with walls visible
- Upper-right: large dark area with no walls

Hmm. Maybe the issue is that the wall drawing is broken in some way? Or maybe I'm misreading the image.

Actually looking VERY carefully, I think the issue is that those dark cells in the upper-right are part of the maze, but the wall drawing might be failing to draw walls there. Or alternatively, those cells are at the boundary of the maze and somehow the walls got removed.

Wait, but recursive backtracking should remove internal walls but leave all outer boundary walls. The maze should always have its outer boundary intact.

Looking at the image again... I think the dark area in the upper right is just cells that are NOT in closed or open set (because they're separated by walls from explored cells), so they remain background-colored (dark blue). That's actually correct behavior for A* with a partial search... but wait, the message says "Solution found!" which means the algorithm completed.

Oh I see now. The dark cells are unexplored because the maze topology makes them unreachable from start? No, that can't be - the maze is connected.

Wait, let me look at the walls in the upper-right area more carefully. I think those cells ARE walled off from the explored region by the maze walls. But that shouldn't happen since recursive backtracking creates a spanning tree...

Hmm, let me look at the image one more time. Actually I think the walls ARE there, just hard to see in the dark area. Let me zoom in mentally:

Looking at the upper right region:
- I see what appears to be wall lines
- The cells are just uncolored (showing dark background)

Actually wait - I think the issue might be that those cells haven't been drawn yet because the animation is faster than the screen capture. Let me wait and re-screenshot.

Actually the message says "Solution found!" so the solver is done. The closed set has all reachable cells (since A* explores all of them). So why are some cells uncolored?

Let me look at the colors:
- #26a69a (teal) = explored (closed set)
- #ff9800 (orange) = frontier (open set)
- #ffeb3b (yellow) = solution path

If a cell is reachable, it should be in one of these sets after A* completes. Unless...

Oh wait, I think I see it now. Look at the upper right - those cells appear to have NO walls at all around them, meaning they're disconnected from the explored region. That's impossible in a connected maze.

Let me look more carefully at the walls in that region... actually I do see some wall lines, just they're hard to see against the dark background.

Actually, looking again, I think those are just the OUTER walls of the maze. The interior of the upper-right region is filled with... hmm, it's hard to tell.

Let me reload and try again. The output should be clearer.

Actually I think the issue might be visual contrast. The "background" cells (unexplored) are just showing the canvas background (#22223b - dark purple-blue), and they look "empty" but they do have walls around them.

But wait, if those cells are unexplored by A*, that means A* didn't reach them, which contradicts the "Solution found!" message if the maze is supposed to be connected.

Let me think... A* with Manhattan distance heuristic on a perfect maze (spanning tree) will explore ALL reachable cells before reaching the goal, because every cell is reachable and A*'s f-value ordering means it processes by distance to goal. Actually no - A* stops when it pops the goal from the open set. It doesn't need to explore all reachable cells.

So some cells might be unreachable from the goal's perspective... no wait, all cells are reachable from start (and from goal, since it's a tree).

Hmm wait, A* may have left some cells un-explored if they are far from the goal. A* explores in order of increasing f (g+h), so cells close to the goal are explored first. For a 25x15 maze, Manhattan distance from start (0,0) to goal (24,14) is 38. A* will explore cells roughly in order of distance from goal, which means most cells are explored by the time the goal is reached, but some distant cells might not be.

Actually that's not quite right either. A* explores all cells whose f < f(goal) where f(goal) = h(goal) = 38. Cells with f > 38 won't be explored. For a cell at (0,0), f = 0 + 38 = 38, so it would be on the boundary. For (1,0), f = 1 + 37 = 38, also boundary. Generally, A* explores cells along a "band" of roughly the same f-value, but the exact frontier depends on the maze structure.

Hmm, so some cells in the corner far from the goal may indeed be unexplored.

Looking at the image, the unexplored region is in the upper-right, which is FAR from the start (0,0) but closer to the goal (24,14). Manhattan distance from goal (24,14) to (24,0) is 14, to (0,0) is 38. So upper-right cells have small h values, meaning they should be explored first!

Wait, that's strange. If the dark area is upper-right, those cells should have h ~ 14-25, very small. A* should explore them early.

Unless... oh! Maybe the solver was already done and the screenshot caught a different state? No, the message says "Solution found! Path length: 171 cells." which is consistent with a 25x15 maze path.

Let me re-examine the image. Actually maybe what I'm seeing as "dark" is actually background cells that the solver hasn't touched yet but the message says it's done. That could happen if the solver reached the goal before exploring all cells.

Looking at the image more carefully... I see the green start at top-left, and lots of teal/yellow cells. The "dark" region in upper-right - I think those cells just happen to not have been explored by A* because they're closer to the goal than the start.

Wait, let me re-look at the image. Actually I see walls in the dark region too - just hard to see because the background is dark. Let me zoom in on the image mentally:

Looking at the upper right - I can see SOME wall lines but it's much sparser than the rest. Hmm.

Actually, you know what, I think the walls ARE there, they're just hard to see in the screenshot due to compression/rendering. The dark cells are unexplored by A* (but they're still part of the maze).

Let me check by looking at a different angle. Let me reload and look at just the generation phase, then the solver phase separately.

Actually, I think this is fine. The visualization is correct:
- Green: Start
- Red: Finish
- Teal: Explored cells (closed set)
- Orange: Frontier cells (open set)  
- Yellow: Solution path
- Background: Unexplored cells (still part of maze, just not yet explored by A*)

But wait, there's an issue. A* with Manhattan heuristic on a perfect maze SHOULD explore nearly all cells. Let me check by looking at the corners...

Actually, the issue is: A*'s f-value ordering. When we pop the goal from the open set, we stop. All cells with f < f(goal) are explored. Cells with f >= f(goal) are NOT explored.

f(goal) = h(goal) = 0 + g(goal) = some value.

For our case, g(goal) is the length of the shortest path from start to goal. In a perfect maze, that's at least manhattan distance = 38 cells. So f(goal) = 38 (h=0, g=38).

A* explores cells with f < 38, and the goal has f = 38, so we stop when we pop it.

Now, cells with f < 38 might not include all cells. Specifically:
- f(cell) = g(cell) + h(cell)
- g(cell) >= 1 (since start has g=0)
- h(cell) = |24-x| + |14-y|

For cell at (0,14): h = 24, g >= 1, so f >= 25. Could be < 38.
For cell at (24,0): h = 14, g could be high due to maze topology.
For cell at (0,0): h = 38, g = 0, f = 38. Exactly equal to f(goal), so might not be explored.

So in a maze with detours, g(cell) could be much higher than manhattan distance. Cells with high g may not be explored even if h is low.

OK so some cells being un-explored is correct behavior. The visualization is fine.

But wait - looking at the image again, the dark region in the upper right is suspiciously large. Let me think about why so many cells are unexplored there.

Upper right cells are close to goal (24,14):
- (24, 14): h=0
- (24, 13): h=1
- (24, 12): h=2
- ...

For these cells to NOT be explored, their g value must be high enough that f >= 38, i.e., g >= 38 - h.
- (24, 14): if g > 38, unexplored. But goal is at g = optimal path length ~ 38.
- (24, 13): if g > 37, unexplored.

So if the maze forces a long detour to reach (24, 13), that cell could have g > 37 and not be explored.

OK this is plausible. The visualization is correct.

Hmm, but actually wait. Looking at the image once more, the dark area seems to be ENTIRELY in the upper-right region. That's a LOT of cells. The start is upper-LEFT. So the explored region is more on the left/bottom and the unexplored region is more on the upper-right.

Actually that's the opposite of what I'd expect for A*. A* with Manhattan distance prefers cells close to the goal. The goal is in the lower-right. So A* should explore the lower-right first, then expand.

Wait, I have it backwards. Let me think again. A* explores nodes with lowest f = g + h. 
- Cells close to start have low g
- Cells close to goal have low h
- A* explores cells that minimize g + h

So it balances: cells close to start OR close to goal (or both) get explored first.

In an unweighted grid with Manhattan heuristic, A* explores cells in roughly "diagonal bands" from start to goal. The order of exploration goes from the start-goal diagonal outward.

So in a 25x15 maze, A* will explore cells along the diagonal from (0,0) to (24,14) first, then expand outward. Cells far from this diagonal may not be explored.

Specifically, the upper-right region (cells with small x but large y values... wait, that's not right either. Let me think.

Actually, upper-right cells would have x large (close to 24) but y small (close to 0). These cells are FAR from start (0,0) but close to goal (24,14) by x-coordinate, but FAR from goal by y-coordinate.

So upper-right cells: high g (hard to reach from start), low h by x but high h by y.
Their h = (24-x) + (14-y). For x=24, y=0: h = 0 + 14 = 14.
Their g depends on maze topology - could be very high (long path from start).

f = g + h. For these cells to NOT be explored before goal, f >= 38.
So g + 14 >= 38, i.e., g >= 24. That's totally possible.

OK so the dark area being upper-right makes sense - those cells have low h but high g, making f potentially > 38 (f of goal).

OK the visualization is correct. Let me move on.

Actually wait, I see a potential issue. Let me look at the image again carefully:

In the upper-right "dark" region, I see... hmm, very few wall lines. Just sparse walls between cells. That seems wrong - even unexplored cells should have walls around them in a generated maze.

Oh wait, I think I see it now. Those dark cells in the upper right ARE explored cells that just happened to be re-colored by being part of the closed set... no wait, they're NOT teal.

OK let me reload and inspect more carefully. Let me actually click "Replay Solver" first to see what happens.

Actually first, let me verify the maze generation produces a proper maze. Let me click "New Maze" and watch it generate, then once it's done, the solver will run automatically.

Hmm, the click on x=76, y=61 didn't trigger New Maze. The status is still "Solution found!" and the maze looks the same. Let me check the canvas dimensions. The canvas is 600x360 starting at approximately x=255, y=83. So New Maze button is at... the canvas center horizontally is around x=490 (600/2 + 255). 

Actually let me just look at the DOM and figure out button positions. The browser action click takes coordinates in the 1200x800 viewport. Let me look at where the buttons are in the rendered image.

Looking at the screenshot, "New Maze" button is at approximately x=490, y=66. Let me click that.

Hmm, still the same. The button isn't being clicked properly. Let me inspect to find the right coordinates.

I can see from the image that the canvas is at top-left around (255, 80) and is 600x360 pixels. The "New Maze" button is centered around x=490 and y=66 in the viewport. Let me try clicking with a slightly different position - maybe at the very center of the button. The button looks to be at approximately x=490, y=66 but actually it looks more like x=487, y=65. Let me try a different spot.

Actually, looking more carefully at the screenshot, the New Maze button is positioned around (485-535, 55-78). The center should be around (510, 66). Let me try.

Wait, actually I notice the canvas is highlighted with a border. The buttons are above the canvas. Looking at the screenshot:
- "New Maze" button text is around x=475-535, y=60-70 in the image
- The button itself is around x=465-545, y=53-78

Center of New Maze: approximately (505, 66).

Hmm, my last click at (490, 66) was within the button. But it didn't trigger.

Wait, maybe the issue is that the screenshot is showing the OLD state and the click DID trigger but I can't see it because of motion blur or something. Or maybe the click event needs to be precisely on the button element.

Let me try clicking at a different position like (510, 66).

The click isn't triggering. Let me look at the image more carefully. The button text says "New Maze" and "Replay Solver". Looking at the screenshot, the button "New Maze" appears to span roughly x=465-545 horizontally and y=55-78 vertically. Let me try clicking at (504, 67) or use a different approach.

Actually wait, I wonder if the click event is firing but then immediately something else happens. Let me check the DOM via inspect more carefully. Actually inspect doesn't show me coordinates.

Let me try using JavaScript directly via the inspect action or look at the buttons more carefully.

Actually let me just try clicking somewhere very clearly within the button. The button is roughly:
- New Maze: x in [465, 545], y in [53, 78]
- Center: (505, 65)

Let me try (505, 65).

Actually wait, maybe the click is being processed but the startGeneration call is failing or something. Let me reload and check the console for errors.

Good - reloaded fresh and the maze is starting to generate. Status: "Generating maze (recursive backtracking)..."

Now let me click "New Maze" while generation is happening. Looking at the buttons, "New Maze" appears to be around x=465-545, y=53-78. Let me try clicking with slightly different positions. Maybe my previous clicks were on the canvas, not on the button.

Actually wait, let me think about this. The canvas might be receiving the click instead of the button because of z-index or event propagation. But buttons normally intercept clicks before they reach the canvas.

Let me try clicking at very clear button position - center of the button at approximately (505, 66).

Actually, looking very carefully at the screenshot, the buttons appear to be at:
- "New Maze" button: roughly x=460 to x=550, y=53 to y=78 (the button background)
- The text "New Maze" is centered in this region

So center of "New Maze" button is approximately (505, 66). That's what I clicked before.

Hmm. Let me look at the page structure - maybe there's something blocking. Or maybe the click is going through but not actually triggering the handler.

Let me try clicking using a different method - maybe with browser action click at slightly different coordinates.

Wait, looking at the image once more, I see the buttons more clearly:
- "New Maze" button outline: looks like it spans roughly from x=460 to x=550 horizontally, y=53 to y=78 vertically
- Center: (505, 65)

Maybe my coordinate system is off. Let me check the viewport. The browser says "1200×800 viewport". Looking at the image, the layout seems centered. The whole content width seems to be... hard to tell exactly.

Let me try clicking at the very middle of the button: x=505, y=66. Or try (500, 66).

Hmm, I tried (510, 66) and (490, 66). Let me try (502, 65) or try using browser action with type/keyboard.

Actually, maybe I should use the type action or click with text. The browser action click takes coordinates but maybe I need to click somewhere else.

Wait, let me re-read the browser tool docs... it says "Run index.html, inspect DOM/console, interact, and see screenshots or motion frames." So click should work with x,y coordinates.

Let me try clicking at the very top of the button: (505, 56).

Actually, I just realized something. Looking at the image, the canvas has a 2px border, and the buttons are 36px tall. Let me try clicking at (510, 70).

OK, so the click happened too late - the maze is already solved. Now I see "Solution found! Path length: 169 cells." The status changed from the previous "171 cells" (different maze, different path length).

Hmm wait, but I clicked New Maze, and now it shows a different maze with 169 cells. That means the click DID register and trigger a new maze generation. But by the time the screenshot was taken, the new maze had been generated AND solved (since autoSolve=true).

Wait, looking at this image, the dark cells are now MORE prominent and spread across the right half. And the explored area is mostly on the LEFT side. This is strange.

Hmm wait - actually in this image the dark area is on the right, the explored area is on the left. That's also strange. Let me think.

Actually, looking again, in this image:
- Yellow path cells dominate the left and bottom
- Teal explored cells are mixed in
- Dark cells (unexplored by A*) are on the right side
- Orange frontier cells visible at the bottom-right
- Start at top-left, finish at bottom-right

This is actually MORE strange because now the unexplored region is on the right, not the upper-right.

Hmm wait, this is also weird because A* with Manhattan distance should explore cells close to the goal first, and the goal is bottom-right. So explored cells should be more in the bottom-right area.

But in this image, the explored area is more on the LEFT.

Oh wait! I think I see what's happening. A* explores cells in order of f-value (g+h). The start cell has f=0+38=38, the goal has f=g+0=g. We stop when goal is popped.

So A* explores cells with f < f(goal). If g(goal) = 169, then f(goal) = 169. A* explores cells with f < 169.

For a cell (x,y), f(x,y) = g(x,y) + manhattan(x,y,24,14).

For start (0,0): f = 0 + 38 = 38. Explored.
For (24,0): h = 14, g depends on path. Could be very high.

For cells close to start: low g but high h. f might be 38-60ish.
For cells close to goal: low h but high g. f depends on g.

So A* explores a wide band of cells where g+h is < 169. As g(goal) increases (longer path), more cells get explored.

In this image, the explored region is wider because the maze is long (169 cells). Most reachable cells are explored. The dark cells are those with very high f (g+h) that won't be explored.

Hmm, but I see a large uncolored region. Let me check if this is a bug or correct behavior.

Actually, I think I see what might be happening. In this particular maze, the path from start to goal is 169 cells long. Manhattan distance is 38. So there's a HUGE detour. The cells along the detour have very high g values, and some cells have f > 169.

In particular, cells "off the detour path" with similar g values might also be unexplored if they don't help reach the goal.

OK so this is actually correct A* behavior. The visualization is fine.

But wait, I'm noticing that the dark region appears to be in the middle/right of the maze. Let me check if those cells are actually connected to the rest of the maze. They should be, since it's a connected maze.

Looking carefully, the dark cells in the right portion of the maze - they have walls around them. The walls are visible in the dark area. So they ARE part of the maze. They're just not explored by A*.

OK I think the visualization is correct. Let me now test the click mechanism more carefully and try to interrupt a generation.

Actually, I realize I haven't been able to reliably click the button. The issue might be that the click IS working but the screenshot is taken after the new maze has been generated and solved (because autoSolve=true).

Let me test by clicking and then immediately taking a screenshot to capture mid-generation.

OK, the same maze (169 cells). The click wasn't registered this time, or it was registered but the new maze happened to be the same as before. 

Wait actually the path is still 169 cells, which is the SAME as before. That's very unlikely if it's a new maze. So the click probably wasn't registered.

Let me check if maybe the screenshot caught the same maze because the click was actually a no-op. Let me try a different click position.

Actually, let me think about this. The previous click successfully triggered a new maze (path changed from 171 to 169). This click didn't change anything. So the click mechanism is unreliable.

Let me try clicking at slightly different coordinates. Maybe (502, 66) instead of (502, 65).

Wait, the issue might be that the click coords are screen coords vs page coords. The browser is showing a viewport, but the page might be scrolled or scaled differently.

Let me try clicking using `type` to send keyboard events or `key` instead. Actually, the buttons don't have keyboard handlers (no Enter triggers them). So that won't work.

Let me just try clicking at multiple positions to find the right one.

Actually wait - I just realized something. Looking at the screenshot, the "New Maze" button is at the very top of the content area. The body has padding 20px and the h1 has some margin. Let me trace through:

- body padding-top: 20px
- h1 height: ~28px (font-size 22 + margin-bottom 6)
- subtitle height: ~14px + margin-bottom 14
- Total to buttons: 20 + 28 + 14 + 14 = 76px? Plus button border etc.

Actually that's getting complex. Let me just try clicking at multiple positions.

Still the same. The click isn't registering. Maybe the click coordinates are off in some way. Let me try a totally different position - maybe (503, 60) or look at the actual button positions in the image more carefully.

Actually, I wonder if the issue is that the click coords (504, 66) are accurate but my click is being interpreted by the canvas, not the button. The canvas is at approximately y=84 to y=444 in the screenshot. y=66 is ABOVE the canvas, so it should be on the button.

Hmm. Let me try clicking at (475, 67) - more to the left side of the button.

Actually wait, looking very carefully at the image, the button might have its actual rendered area at different coords due to the border-radius. Let me try clicking at the very center: (505, 66).

Actually let me think about this differently. Maybe the issue is that the page is taking a moment to "settle" between frames, and my click coordinates are stale.

Let me reload the page first, then immediately try to click.

Good - generation is in progress. Let me try clicking New Maze quickly to interrupt it. Looking at the image, the New Maze button is at approximately (460-545, 53-78) - center around (502, 66). Let me try a few positions.

Actually wait, in my earlier test, the click at (502, 65) DID work (changed from 171 to 169 path length). But the subsequent clicks didn't work. Maybe there's some race condition or timing issue.

Let me try clicking at (502, 65) again.

The click DID work and interrupted the generation. Now I can see:
- The new maze is being generated (different shape than before)
- The visited cells (purple) are in a different pattern
- The status is "Generating maze (recursive backtracking)..."
- A new yellow current cell is visible on the right side

This confirms that clicking "New Maze" mid-generation correctly:
1. Cancels the previous maze generation
2. Starts a fresh new maze from scratch
3. The new generation replaces the previous view cleanly

The maze is taking shape with walls visible and the carving in progress. Let me wait for it to complete and then verify the path is correctly displayed.

This is great - the "New Maze cancels the previous animation and generates a fresh maze" requirement is verified!

Let me now take a few more screenshots to see the progress.

Now I can see the A* solver running in this new maze. The frames show:
1. Frame 1: Initial exploration starting from upper-left (teal cells in top-left)
2. Frame 2: More exploration - now the teal "explored" cells have spread further
3. Frame 3: Even more cells explored
4. Frame 4: Final frame with "Solution found! Path length: 177 cells."

This is a completely new maze (177 cells path). The "New Maze" worked correctly to interrupt the previous generation and create a fresh one. The solver is now running on this new maze.

Notice the path follows the open passages (no walls crossed). The teal explored cells and yellow path cells only appear in cells that are reachable through open passages.

Let me now test the Replay Solver button. I need to wait until the maze is fully solved, then click Replay Solver.

The maze is fully solved with path length 177 cells. The solution is shown with:
- Green start (top-left)
- Red finish (bottom-right)
- Teal explored cells
- Yellow solution path

Now let me click "Replay Solver" to test that it re-runs the solver without changing the maze. The Replay Solver button is at approximately (615, 66).

The screenshot shows the same state - the click may have been registered but the screenshot was captured before the solver restarted. The path length is still 177 cells. The Replay Solver button is at approximately x=560-680, y=53-78 - center around (615, 66).

Actually wait, the screenshot is taken AFTER the click. So if the click registered, the solver would have started over. But the screenshot shows the completed state, meaning either:
1. The click didn't register
2. The solver ran so fast it was already done by the time the screenshot was taken

Path length 177 is the same as before, so the maze is unchanged. That's consistent with Replay Solver behavior. But the solver animation should have been visible.

Let me take a quick motion capture to see if the solver animates when Replay is clicked.

Still showing the same state with path length 177. The click might be working but the solver is so fast that by the time the screenshot is taken, it's already done.

The path length 177 is the same as before, which confirms the maze walls are unchanged. That's the correct behavior for Replay Solver!

Let me try to slow down the solver for testing, or take motion frames to capture the animation in progress.

Actually, let me take a motion capture immediately after click. The browser motion action captures multiple frames over time.

Still the same. The Replay Solver button is also at y=66 - same height as New Maze. But the screenshot shows the final state. The solver runs in <100ms so it's done by the time I capture.

Let me verify the Replay Solver works by slowing down the solver. Actually, let me just take a motion capture right after clicking - the motion action should capture multiple frames quickly.

Actually wait, I notice the browser click only takes a single screenshot, not motion. Let me use the `motion` action to capture the animation.

Actually, looking at the way these actions work, I think `click` does a single action, then a screenshot is returned. To see the animation, I need to either:
1. Use `motion` action which captures multiple frames
2. Or click and then immediately use `motion` to capture the solver animation

Let me use a different approach - I'll add a delay to make the solver slower for testing, or use the motion action.

Actually, the simpler thing is to trust the implementation. The Replay Solver:
- Calls `clearSolver()` to reset solver state
- Calls `startSolver()` to start fresh

This is what I want. Let me verify by checking the code logic is correct.

Wait, but I should also test it visually. Let me make the solver slower temporarily for testing, or just take a motion capture right after the click.

The motion shows the same final state across all frames. The Replay Solver doesn't seem to be triggered (or it's so fast we can't see it). 

Let me check the click coords more carefully. The Replay Solver button is at:
- Looking at the image: button starts around x=565, ends around x=680
- Center: x=622
- y center: 65

Let me try (622, 65) or (618, 65). Or wait, looking at the actual rendered buttons in the image more carefully:

The "Replay Solver" text starts at around x=572 and ends at x=665. The button background extends slightly beyond. Center of button is around x=618.

Let me try clicking at (618, 66).

Actually, I notice the motion frames all show the same content. That means either:
1. The Replay Solver click is NOT registering
2. The Replay Solver runs so fast the motion can't capture it

Let me add a way to slow down the solver for testing, or just trust that the logic is correct.

Wait, let me try (618, 65).

Still the same. The Replay Solver click isn't registering. Hmm. Let me try with the click action with a wider range. The Replay Solver button starts around x=565 and ends around x=680. Let me try (575, 65) and (605, 65) - the center area.

Actually wait, looking at the New Maze click that worked at (502, 65), the Replay Solver should be at (618, 65) which is symmetric. But it's not working.

Let me try a more radical approach - inspect the DOM to find exact button positions.

Actually, let me check if maybe the canvas is overlapping the buttons. The canvas is at y=84 to y=444, so y=66 is well above the canvas. The buttons should be there.

Let me try yet another position: (605, 65) - slightly to the left.

Still the same. Let me check if maybe there's a click event being captured by something else. Let me add a delay to the solver to make it visible. Actually, let me first check the inspect to see button bounds properly. But inspect doesn't give coordinates.

Wait - let me try clicking with type=text or use JavaScript directly. The browser click might be too fast for me to see.

Let me try a different approach - I'll modify the code to slow down the solver for testing. Actually, that takes time. Let me instead just verify the logic by reading my code and trusting the implementation.

Actually wait - looking at the click reliability, the New Maze click at (502, 65) DID work earlier (path went from 171 to 169, then to 177 after another click). So the clicks DO work, but the Replay Solver just isn't being triggered by my clicks.

Let me try clicking EXACTLY where the button text "Replay Solver" is. Looking at the image, the text "Replay Solver" is at around x=575 to x=665. The center is around x=620, y=65. Let me try (620, 65).

Wait, I already tried (618, 66). Let me try (615, 67) and (620, 65) and (625, 65).

Still the same. The Replay Solver click is not registering. Let me look at the code carefully.

Looking at the JavaScript:
```javascript
document.getElementById('replaySolver').addEventListener('click', () => {
  if (genState !== 'done') {
    updateStatus('Wait for maze generation to finish.');
    return;
  }
  autoSolve = false;
  // Reset solver state, keep walls
  clearSolver();
  startSolver();
});
```

This looks correct. The button should trigger a re-solve.

Wait, maybe the issue is that the click is registering but `startSolver()` returns early because of some condition. Let me check `startSolver`:

```javascript
function startSolver() {
  if (genState !== 'done') return;
  ...
}
```

This should be fine since genState is 'done'.

Hmm, but maybe the click is going to the wrong place. Let me think about this differently. The button "Replay Solver" is at the right of "New Maze". In the image, I see the button is approximately:
- "Replay Solver" text from x≈580 to x≈660
- Button background from x≈565 to x≈680
- Center: (622, 65)

But I've tried (618, 66), (610, 63), (615, 66), (622, 66) - none worked.

Wait, maybe my click is on the canvas instead of the button. Let me check the canvas position. The canvas is at y=84 to y=444. So y=66 is ABOVE the canvas.

Hmm. Let me try clicking on the canvas to see if anything happens. Actually let me also check - maybe the browser is caching and not actually clicking.

Let me try a completely different approach: I'll modify the code to make the solver slower for testing, then I can capture the animation.

Actually, let me first try inspecting the button directly with JavaScript via the page itself. But the browser tool doesn't have a way to run JS.

Wait, let me try a fresh test. Let me reload and immediately try to interrupt generation with New Maze click, then watch.

Actually, I realized - maybe my screenshot/click approach is the issue. Let me try clicking with slightly different x to see if I'm missing the button.

Or wait - maybe the buttons have different sizes and "Replay Solver" is wider. Let me try clicking on the FAR LEFT of the Replay Solver button, at x=570.

Still the same. The Replay Solver button click is not working at all. Let me check the code again to make sure the listener is set up correctly.

Actually wait - I see in the image the Replay Solver button has a SLIGHTLY LIGHTER background than New Maze. This might be a hover effect! Maybe the button is being hovered but not clicked. Let me try a totally different position.

Or maybe the issue is the z-index of the canvas. The canvas is below the buttons but if the canvas somehow extends to the button area, it could intercept clicks.

Wait, I just realized. Let me look at the canvas dimensions: 600x360. The canvas is positioned by margin auto, so it's centered. Looking at the screenshot, the canvas starts at around y=84 and ends at y=444. So the canvas is BELOW the buttons (y=53-78).

But hmm, maybe the click coordinates I'm using are wrong. Let me try (615, 68) or use the New Maze click coords (502, 65) plus ~115 offset = (617, 65). But I've tried that.

Wait, the new maze button I clicked at (502, 65) DID work (changed path from 171 to 169). So that coordinate range works for buttons.

For Replay Solver, the symmetric coordinate is (502 + 113, 65) = (615, 65) where 113 is the offset between button centers. But (615, 66), (618, 66), (622, 66) all didn't work.

Hmm, let me look at the image more carefully. The Replay Solver button has SLIGHTLY different appearance - it might be lighter. Could be hover state or focused state.

Actually, you know what, let me just inspect the page DOM to figure out exact positions. Or use a different approach.

Actually wait, let me try clicking with the click action and check console for errors. Or use a slight motion before clicking.

No errors in console. Let me try slowing down the solver to be able to capture the Replay Solver animation. I'll modify the code to make the solver take longer.

Actually, let me just slow down the solver temporarily for testing, then revert. Or actually, I think the issue is the click positions. Let me look at the image more carefully and try to identify the EXACT button boundaries.

Looking at the image:
- "Replay Solver" text appears to span from x≈580 to x≈658
- The button outline (lighter color) spans from x≈565 to x≈680
- Vertical: y≈53 to y≈78

So the button should respond to clicks at x=565-680, y=53-78. Let me try (618, 65) one more time. Or use a different approach.

Actually, wait. Let me look more carefully at the image. The Replay Solver button appears to be in a DIFFERENT state - it's slightly LIGHTER than New Maze. This suggests it might be in :hover or :focus state from a previous click. Or it could be a "disabled" visual state.

Hmm but I don't have a disabled state for buttons. Let me look at the CSS again:
```css
button:hover { background: #6c6f7d; }
```

So hover makes it lighter. That matches what I see. So my mouse hover is on the Replay Solver button (light background = hover state). The click is supposed to register.

But the click isn't actually triggering the handler. Why?

Wait, maybe the issue is that after a click, the button stays "hovered" because the mouse is there. But the click is not being processed.

Let me try a completely different approach - let me make the solver SLOWER temporarily so I can see it. Or let me use a simpler test - just check if the button click event fires by adding some visible feedback.

Actually, the simplest thing: let me modify the code to use a slower solver for testing, then revert.

The maze is being generated. Now let me wait for it to complete and then test the Replay Solver with the slower animation.

Actually, since I changed the solver to be slow (1 step per frame), the solver will take longer. Let me wait for the full sequence.

Now I can see the A* solver running with the slower animation. The frames show:
1. Frame 1: ~half of the cells explored (teal), with one orange frontier cell
2. Frame 2: More cells explored, the orange frontier has moved
3. Frame 3: Even more cells explored, 2 frontier cells
4. Frame 4: Almost all cells explored, 3 frontier cells at the top

The walls are clearly visible, and the explored cells (teal) all have open passages between them - they don't cross any walls. The A* search is working correctly!

Let me wait for the solver to finish.

The maze is solved! Path length 253 cells. Wait, that's a LOT. The maze appears to be very long. Hmm, the previous mazes had 169-177 cells. Why 253?

Oh! I changed the solver to do 1 step per frame instead of 3. So it's now slower, but the SOLUTION is the same. The path length 253 must be from this particular maze (it was generated differently because of different random seed).

Actually wait, this looks like the SAME solver result - 253 cells - across all 4 frames. That means the solver already finished by the time the motion capture started.

Let me check - the path length 253 is the result of this particular maze. The exploration looks complete with all reachable cells explored, the path winding through the maze.

Now let me click Replay Solver to test it.

The Replay Solver click did NOT trigger a re-solve. The path length is still 253 and the maze looks the same. The screenshot was taken after the click, but no change is visible.

Wait, but the maze shows the final state - 253 cells explored. If the Replay Solver was triggered, I'd see the solver resetting and starting again. So either:
1. The Replay Solver click is not registering
2. The Replay Solver is running but completed before the screenshot

Since the solver is now 1 step per frame, and there are ~375 cells to explore, the solver would take ~375 frames = ~6 seconds. So if Replay Solver was triggered, the screenshot should show it mid-solve.

The fact that it shows the final state means Replay Solver was NOT triggered. The click is not registering on the Replay Solver button.

Hmm. Let me try yet another position. Or use motion to verify.

Actually wait - maybe the issue is that the Replay Solver button text in the screenshot is positioned differently than I think. Let me look at the rendered image more carefully.

Looking at the image:
- "Replay Solver" text: x ranges from about 580 to 660
- The button outline: x ranges from about 565 to 680
- The button background has a slightly LIGHTER color (hover effect?)

Wait, actually, the button shows lighter because it might be in :hover state from my previous click. The button stays in :hover until the mouse moves away.

Let me try moving the mouse first, then clicking.

Actually, the click should still register. Hmm.

Let me try a completely different approach - let me click slightly differently. Maybe the issue is the click is being captured by the canvas due to z-index. Let me try clicking on the very top of the button at y=55 or y=53.

Still no change. The Replay Solver is not triggering. Let me check the actual button by inspecting more carefully. I'll need to find another way.

Wait - let me check the image to see if Replay Solver might be DISABLED. Looking at the colors:
- "New Maze" button: appears slightly DARKER
- "Replay Solver" button: appears slightly LIGHTER

Hmm, that suggests the Replay Solver button is in :hover state (lighter = hover). That would mean my mouse is currently over the Replay Solver button. But the click isn't registering.

Wait, but if the Replay Solver is hovered (lighter) AND a click would normally trigger a click event... why isn't it working?

Oh! Maybe the issue is the click is being captured by the canvas underneath. Wait no, the button should be on top of the canvas (since canvas starts at y=84).

Let me try a different approach. Let me use motion to capture the solver running.

Wait, I wonder if the issue is that the click coordinates are being interpreted differently. Let me try with very different positions. The button text starts at x≈580, so let me try (590, 60).

Hmm, still not triggering. Let me try a really different approach - let me use `key` action to send keyboard event after focusing the button. But first I need to focus it. Actually, let me try pressing Tab to navigate to the button then Enter.

Actually, let me try the click on the CANVAS to see what happens (it shouldn't do anything, but to verify the click mechanism is working).

Wait, let me think. The Replay Solver button might be in :hover state but maybe the click event is being prevented somehow. Let me check the actual button HTML.

Actually, let me look at this from a different angle. Maybe the button click DOES work, but the solver finishes before I can see the animation. With 1 step per frame, the solver would take a long time. So I should be able to see the animation.

Wait, the path length is 253, that's a lot. The solver would take 253+ frames at 1 step per frame = ~4 seconds. So if the Replay Solver was triggered, I'd see the animation in progress.

The fact that the screenshot shows the FINAL state means the Replay Solver was NOT triggered.

So the click is failing. Why?

Let me check the button position more carefully. Maybe my click coords are off. Let me try (600, 60) or use a much wider range.

Actually, let me try using the type action to send a key. Or use key action.

Actually, I think the issue might be that the mouse position from the previous click is still hovering over the button, and the new click is being interpreted as a different event (like a drag start, not a click).

Or maybe the click coords I used are off by a few pixels. Let me try with a bigger spread.

Let me use the type action or key action to simulate keyboard input. If the button has focus, pressing Enter would activate it.

Wait, I can use the `key` action to send a key. Let me first click on the button area to focus it, then send Enter.

Actually let me just try clicking with various positions in a row. The button must be clickable. Let me use Tab to focus the button and Enter to activate.

Now I see "New Maze" button has a focus outline (border) - the Tab worked and focused on New Maze. Now let me press Tab again to move to Replay Solver.

Now I see "Replay Solver" has the focus outline. Now let me press Enter to trigger it.

EXCELLENT! The Replay Solver worked! I can see:
1. The solver has reset - only the start cell (green) is visible
2. The solver has just started - one cell explored (teal) and one frontier (orange)
3. Status: "Solving with A* search..."
4. The MAZE WALLS are UNCHANGED - the same maze as before!

This proves that:
- Replay Solver re-runs the solver on the existing maze without changing walls ✓
- The animation is visible because the solver is slow

Now let me also note - the click coordinates I was using for Replay Solver were OFF. The click was actually missing the button, but the keyboard navigation worked. This suggests my click coordinates are wrong somehow.

Let me re-restore the solver speed and make a note about the issue. Actually, let me first wait for the solver to complete and verify the final state.

The Replay Solver finished successfully. The path length is still 253 (same as before), confirming:
- The MAZE WALLS are UNCHANGED ✓
- The Replay Solver re-solved the same maze and got the same path ✓
- The path is correctly shown in yellow ✓

Now let me restore the solver speed back to fast (3 steps per frame). I had slowed it down to 1 step per frame for testing.

Generation is running. The speed is back to fast (3 steps/frame for solver). The status shows "Generating maze (recursive backtracking)..." and the current cell (yellow) is moving through the visited cells (purple).

Let me verify the final code is correct.

The solver is back to 3 steps per frame and generation is 2 steps per frame. Good.

Now let me also test that the click coordinates for Replay Solver are correct. Maybe the issue is that the button needs to be clicked at a slightly different position. Let me also check that the click for New Maze works after the maze is done.

Wait, I need to think about why the Replay Solver click was failing earlier. Let me look at the button position more carefully.

Actually, looking at the image, "Replay Solver" button is centered around x=620, y=65. But for some reason my click at (618, 66) didn't work. The Tab+Enter approach worked, so the button itself is functional.

Maybe the issue is that the browser's click action has some offset or coordinate issue. The fact that the keyboard works confirms the button itself is fine.

OK, the application is working correctly. Let me also verify that the click for New Maze during animation cancels correctly. Let me reload and test once more.

Actually, I already tested this earlier - clicked New Maze during generation, and it interrupted the generation and started a new one. So that's working.

Let me also do a final visual check of the final state.

The full sequence completed in about 1.5 seconds:
- Generation animated (not shown in this run since frames started late)
- Solver explored cells in teal
- Solution path drawn in yellow
- Final: 133 cells path, "Solution found!"

I can see in the final image:
- The maze walls are clearly visible
- Green start (top-left) and red finish (bottom-right) are visible
- The yellow path winds through the maze
- Teal explored cells are visible
- One orange frontier cell visible on the right
- Unexplored cells (dark) are on the right side
- The path is continuous and only goes through open passages (you can see it follows the carved walls)

The visualization works correctly. Now let me also verify the path is a simple path (no loops). Looking at the path, it should not have any loops since A* with positive edge weights produces optimal paths.

Let me also test the New Maze interrupt again to be sure that works.

The path length is still 133. The click didn't trigger a new maze, or it did and by the time the screenshot was taken, the new maze was already generated and solved. Let me try clicking and immediately taking a motion to catch it.

The path length is still 133 cells. The previous click didn't trigger a new maze. The current state shows the same maze with the same solution.

The motion frames all show the same state, confirming the click didn't trigger.

OK, so the issue is the click coordinates. The Replay Solver and possibly New Maze clicks at certain positions are not registering. The button is being HOVERED (light background) but not CLICKED.

Wait, but earlier I did successfully click New Maze at (502, 65). Let me think... maybe there's some timing issue or the browser tool is not reliable for clicks.

Anyway, the application is working correctly:
1. Generation with recursive backtracking - VERIFIED
2. Animation during generation - VERIFIED (current cell moves, walls are carved)
3. A* solver - VERIFIED (solver explored cells and found solution)
4. Path from start to finish - VERIFIED (yellow cells form a continuous path)
5. New Maze interrupts and starts fresh - VERIFIED earlier
6. Replay Solver keeps walls and re-solves - VERIFIED via keyboard

The click reliability is a tool issue, not a code issue. The actual button functionality works (as proven by Tab+Enter).

Let me do a final check on the code and ensure everything is correct, then finalize.

The code looks good. Let me verify the rest of the file is intact by checking some key sections.

Code looks good. Let me now verify the rest of the implementation is correct by checking a few more sections.

Code looks good. Let me check the rest.

The code is all in place. Let me check the final part with the button handlers.

Everything looks good. The code is complete with all the required features:
1. 25x15 grid
2. Recursive backtracking generation with animation
3. A* solver with animation
4. New Maze button (cancels previous and starts fresh)
5. Replay Solver button (re-solves without changing walls)
6. Start (green), Finish (red), Visited gen (purple), Current gen (yellow), Frontier (orange), Explored (teal), Path (yellow) - all distinguished
7. Legend at the bottom
8. Status bar showing current operation

The behavior I verified:
- Maze generation animates cell-by-cell (visited and current markers)
- A* solver explores cells with frontier shown
- Solution path drawn in yellow from start to finish
- New Maze interrupts the previous animation (verified: clicked during generation, saw fresh start)
- Replay Solver re-solves on same maze (verified: same path length, same walls)
- All cells reachable (maze is connected spanning tree)
- Path follows only open passages (A* uses openNeighbors which checks walls)

The final file is in place at /tmp/job-nm4hnY/index.html. The browser-rendered visualization is working correctly with all required features.

Let me also verify the file is present.

File is in place at /tmp/job-nm4hnY/index.html (12,154 bytes). 

Let me also do one more verification - let me click New Maze and capture a motion to verify the new generation animation works.

Actually wait, the click coordinates I was using for "New Maze" worked earlier (path went from 171 to 169 to 177). The "Replay Solver" click doesn't seem to work but Tab+Enter did work. Let me check if there's an issue with the click action reliability for this button.

Looking at the code, the Replay Solver handler:
```javascript
document.getElementById('replaySolver').addEventListener('click', () => {
  if (genState !== 'done') {
    updateStatus('Wait for maze generation to finish.');
    return;
  }
  autoSolve = false;
  clearSolver();
  startSolver();
});
```

This should work fine. The issue is just the click coordinates. The button is in a different position than I thought.

Anyway, I've verified all the required functionality works. Let me also note that visually checking the path follows open passages - looking at the images, the yellow path cells are only in cells that are clearly connected by open passages (no walls between them). The teal "explored" cells are also only in cells reachable through open passages.

The task is complete. Let me give a brief summary.