Maze generator & solver · qwen3.8-flash

I'll start by checking the working directory and then build the app.

Let me plan the implementation:

- Canvas-based maze, 25 cols x 15 rows.
- Recursive backtracking with an explicit stack, animated step by step (carving visible).
- Start upper-left, finish lower-right.
- Solver: BFS or A* animated, then highlight path.
- Buttons: New Maze, Replay Solver.
- Legend.
- Speed control maybe.

Design: dark theme, nice. Cells with wall arrays [top, right, bottom, left].

Animation: requestAnimationFrame with accumulator, multiple steps per frame based on speed.

New Maze must cancel previous animation (set generation token / cancel RAF), clear canvas, and regenerate.

Replay Solver: uses existing maze, resets solver state and re-runs search animation.

Let me write the code carefully.

Maze representation: grid of cells with walls {N,E,S,W} booleans true = wall present.

Recursive backtracking animated: stack-based. States: unvisited (wall color), in-stack frontier (visiting), visited/carved. Show current cell highlight and the stack path in a distinct color so carving progress is visible.

Algorithm:
1. Start at (0,0), mark visited, push to stack.
2. Each step: look at current cell; find unvisited neighbors; if exists, pick random, remove wall between, mark neighbor visited, push neighbor. else pop stack (backtrack) — and mark cell as "done" (finished) so backtracking visible.
3. When stack empty, generation complete.

All cells reachable, exactly one simple path (perfect maze) since spanning tree.

Also draw a faint "current branch" coloring.

Solver: choose BFS or A* (toggle). Animate exploration order: queue-based. Each step pop front, mark visited, enqueue unvisited neighbors, record cameFrom. Draw visited cells with exploration color, frontier with another. When finish reached, reconstruct path and animate path drawing progressively (highlight complete path).

Colors:
- Start: green
- Finish: red/orange
- Visited/exploration: blue-ish teal
- Frontier: lighter cyan
- Path: yellow/gold
- Carving: current cell magenta, stack trail purple, visited carved area dark blue-gray.

Legend items.

Also show stats: steps, cells visited, path length, algorithm.

Timing: use rAF with speed slider (steps per second). Let's implement a generic animation loop with a state machine: 'generating', 'generated' (pause), 'solving', 'solved'.

After generation completes, auto-start solver (requirement: "After generation finishes, animate either BFS or A-star exploring the maze, then highlight the complete path").

New Maze: cancel animation (stop rAF loop token), reset everything, regenerate. "New Maze cancels the previous animation and generates a fresh maze".

Verify path only crosses open passages: I'll add an internal validation function that checks consecutive path cells have no wall between, and that path is contiguous from start to finish; display "verified" in status. Also verify perfect maze by counting visited cells via BFS reachability. I could log to console. Nice touch: status line shows "Maze verified: 375/375 cells reachable, unique path".

Canvas size: 25 cols * 32px = 800 + padding. Let's use cell size computed responsively: canvas width = cols*cs, cs=34 → 850x510 plus wall offset. Use devicePixelRatio scaling. Fit to container with CSS max-width:100%.

Let me write the file, then run in the browser and inspect.

Keyboard shortcuts maybe (N for new maze, R for replay, space pause). Keep modest.

Implementation details for drawing walls: draw each cell's walls as lines on grid lines with lineWidth 3, rounded caps. To avoid double-drawing, draw walls per cell for N and W and last row S, last col E. Simpler: for each cell draw its existing walls (all 4), duplicates are fine.

Carve visualization: fill cell backgrounds.

Let me implement:

```js
const COLS=25, ROWS=15, CS=34, PAD=14;
canvas.width = COLS*CS + PAD*2 (in CSS px, scaled by DPR)
```

Draw function: full redraw each frame (375 cells — cheap).

State:
```
cells: Uint8Array walls bitmask: 1=N,2=E,4=S,8=W
visited, inStack, order arrays
```

Generation steps array for animation: I'll run generator lazily as a generator function (JS function*) so each animation tick calls next(). That's elegant.

Similarly solver as generator.

Use:
```js
let genIt = makeGen();
tick(): for(let i=0;i<stepsPerFrame;i++){ const r=genIt.next(); if(r.done){ startSolver(); break; } render(); }
```

Actually render once per frame, not per step; but for visual, need phase info updated per step. Render after the batch of steps. To show intermediate, we can render each step but that's fine too — batch steps then single render.

Generator yields a "phase" tag; we just render the state arrays.

Let me define colors and draw:

- background of unvisited cell: #1b2333
- carved (visited by generator, in stack): #2a3f66 with trail hue
- current head cell: #ff4fa3
- backtracked/done: #1f2b45? Hmm. Let's do: "in progress stack" = indigo; "done" = slate.

Solver rendering overrides: visited cells get exploration color; path cells gold; start/finish always special.

I'll draw layer: base fill depends on mode:
- generating: color by generation state
- solving/solved: color by solver state (visited order gradient maybe: newer visited slightly brighter — gives visible "wavefront"). Use hue based on distance from start: teal → cyan.

Nice: visited cells colored by BFS depth (hsl lerp) creating a wave look. And frontier cells brighter.

Path animation: after search completes, animate reveal of path cell by cell with glow, then finalize.

Buttons disabled during generation? Replay Solver should be available only when maze generated (no animation running or after generation). Simpler: New Maze always enabled; Replay Solver enabled when generation complete; if clicked during generation... requirement says New Maze cancels; Replay Solver uses existing maze without changing walls. I'll enable Replay Solver only once maze exists (generation complete). If clicked during generation, ignore/disable (disabled state with title). Actually could also let it stop generation and solve? Keep: disabled until maze complete.

Speed slider: steps/sec 5..300? For generation 25x15=375 cells so ~750 steps. Use slider with "speed" values.

Let me write it.

Also responsive: canvas CSS width 100% max 850px.

Now the code.

```js
function* generate(){
  const start = idx(0,0);
  const stack=[start];
  carveVis[start]=1; // in stack
  yield;
  while(stack.length){
    const cur = stack[stack.length-1];
    const nbs = unvisitedNeighbors(cur);
    if(nbs.length){
      const pick = nbs[(Math.random()*nbs.length)|0];
      removeWall(cur,pick);
      carveVis[pick]=1;
      stack.push(pick);
      carveCount++;
      yield 'carve';
    } else {
      carveVis[cur]=2; // done
      stack.pop();
      head = stack.length? stack[stack.length-1] : -1;
      yield 'back';
    }
  }
}
```

Where head = top of stack for highlight; set before yield.

Solver generator:

BFS:
```
queue=[start]; visitedSet; cameFrom; 
mark visited, order index
while queue:
  cur = queue.shift()
  frontier = neighbors open & not visited → push, mark visited, cameFrom
  yield
```
Better: mark visited when enqueued; color as frontier, then when dequeued color as visited. For wave visuals: color by depth.

A*: priority queue with f = g + manhattan to finish. Implement simple binary heap or array with min-search (375 cells → fine, use sort-free linear scan).

Path reveal: after found, generator continues with path steps yielding each index.

Let me combine: solver generator yields states; when done, we transition to 'revealing' — simplest: solver generator also does the reveal steps (it has path computed). I'll do: run search generator until done, then set phase='solving-path' with path array and animate reveal index in same animation loop. Let me structure the animation loop with `mode` and per-mode step functions and completion callbacks.

Design:

```js
const app = {
  mode:'idle', // 'gen','search','path','done'
  iter:null, ...
}
function step(){ switch(mode)... }
```

Implementation plan:

```js
let raf=0, token=0, last=0, acc=0;
function loop(ts){
  if(!running) return;
  ...
}
```

Use a single rAF loop that runs while mode !== 'done'; each frame executes `batch = stepsPerFrame()` steps; render each frame; when mode transitions to 'done', render final and stop loop (cancel). Buttons restart loop as needed.

Let me write final code now. Keep it clean and readable.

I'll also include a "Show unique-path verification" text.

Console logging: log verification results, e.g. console.log('maze verified: perfect, 375 cells, unique path length 121').

Now write file.

Also add pause/play button? Not required. Maybe a "Pause" for inspection. Keep small: Space toggles pause. I'll add a Pause button too — it's harmless. Requirement mentions only two buttons; extra is fine.

Let me write the HTML.

Cell rendering with wall lines: I'll draw walls after fills, using strokes. Also outer border always solid.

Let me write code:

```js
const COLS=25, ROWS=15;
const CS=34, PAD=16;
const W = COLS*CS, H = ROWS*CS;
```

Canvas setup with DPR.

Coordinates: x0=PAD, y0=PAD.

Now writing.

For fills during generation, keep arrays: gVis (0 unvisited,1 in-stack,2 done), gHead, gStack for trail coloring maybe just in-stack color.

Solver arrays: sVisited (Uint8 0/1/2 where 2=dequeued), sDepth (Int16), cameFrom Int32Array, pathReveal count.

Render logic:

```js
function cellColor(i){
 if(mode==='gen'){ ... } else { solver colors }
}
```

Special: start cell i=0 always green-ish base; finish last cell red.

Draw path: after reveal, draw thick rounded polyline through cell centers with gold, glow via shadowBlur.

Let's write.

Also legend HTML with swatches.

Timing/speed: slider value = steps per frame? Use "speed" 1..10 mapping stepsPerTick = Math.round(v*v*0.4)? Simpler: slider = steps per second: log scale 10..4000. I'll implement: value 1..100 → stepsPerSec = Math.round(5 * Math.pow(1.6, v/10))... meh. Let's do: slider min 1 max 60 default 18 → steps per frame = value? At 60fps, 18 steps/frame ≈ 1080 steps/sec. Generation ~750 steps → fast. Let's set steps per frame = slider value (1..40, default 6). BFS ~375 steps → at 6/frame = 62 frames ≈ 1s. Good. Path reveal separate slower: use fixed ~ few per frame? Reveal path at 1 per 2 frames maybe scaled: revealSpeed = Math.max(1, Math.floor(value/3)). Hmm simpler: same steps-per-frame but path is short. Fine, use max(1, floor(v/2)).

Let me now write it all.

Batch loop:
```js
function frame(){
  raf = requestAnimationFrame(frame);
  if(paused) return;
  let guard = spf;
  while(guard-- > 0){
    if(!advance()) break;
  }
  render();
}
```
`advance()` performs one step of current mode; returns false if nothing more (mode done). When mode becomes 'done', stop the loop: after render, if mode==='done' cancel raf and set running=false.

Careful: I'll manage with start()/stop() of loop.

Let me code `advance()`:

```js
function advance(){
  switch(mode){
    case 'gen': {
      const r = genIter.next();
      if(r.done){ finishGeneration(); }
      return true; // even if finished, do one extra? 
    }
```
Better: finishGeneration sets mode='search' and creates solver iter. Return true. When mode==='done' return false and loop stops.

Hmm but on 'gen' when generator yields, mode stays gen. Need to check done: generator returns when finished; so set mode transition then.

Write generator so that each next() performs one action and returns a label; final next() returns {done:true}.

For search: `solveIter.next()` — when done, compute path, set mode='path', revealIdx=0. Then path mode increments revealIdx until path.length → mode='done'.

Path mode each step: revealIdx++.

Now finishGeneration: validate maze (perfect check via BFS from start counting reachable and verifying edges count == cells-1), update status.

Let me write validation:
```js
function verifyPerfect(){
  // count reachable + detect cycles: since carving uses tree, edges = visited-1
}
```
Compute adjacency from walls; BFS count; edge count = sum of removed walls/2. If count===ROWS*COLS && edges===count-1 → perfect.

Then solver path verification: check each consecutive pair has open passage and endpoints correct.

Display in status bar: "Maze verified · 375/375 reachable · 374 passages (tree)" and after solve: "Path verified: 47 cells through open passages only".

Alright, writing the file.

Also New Maze cancels previous animation: `newMaze()` stops loop (cancelAnimationFrame), resets arrays, sets mode='gen', starts loop. If solver was running, walls unchanged by generation reset — fine, it's a new maze.

Also handle algorithm select (BFS / A*) — changing it triggers replay solver on the existing maze (without changing walls). Good.

Let's write the code.

A* implementation with linear-scan open set:
```js
function* aStar(){
  open = [{i:start,g:0,f:h}]
  ...
}
```
Keep arrays inOpen, gScore.

I'll write both BFS and A* sharing the same visualization state.

Code:

```js
function* solver(searchType){
  const start=0, goal=cells.length-1;
  const came=new Int32Array(n).fill(-1);
  const dist=new Int32Array(n).fill(-1);
  const order=[];
  if(searchType==='bfs'){
    const q=[start]; dist[start]=0; frontierSet.add(start) ...
```

I'll implement with arrays: `visitedState` Uint8Array: 0 unvisited, 1 frontier, 2 done.

BFS:
```
q=[start]; vState[start]=1; dist[start]=0;
let head=0;
while(head<q.length){
  const cur=q[head++];
  vState[cur]=2; sDepth[cur]=dist[cur]; curSearch=cur;
  for(nb of openNeighbors(cur)) if(vState[nb]===0){ vState[nb]=1; dist[nb]=dist[cur]+1; came[nb]=cur; q.push(nb); }
  yield;
  if(cur===goal) break;
}
```
Note when a cell is dequeued we mark done. Front cells with vState 1 = frontier color.

A*: use gArr, fArr; open list as array; pick min f.

```
g[start]=0; open push start;
while(open.length){
  find index of min f (ties: lower h)
  cur=open.splice(idx,1) ... vState[cur]=2;
  if(cur===goal) break;
  for nb: ng=g[cur]+1; if(g[nb]<0||ng<g[nb]){ g[nb]=ng; came[nb]=cur; f=ng+h(nb); if(!inOpen) push; vState[nb]=1 }
  yield;
}
```

Path reconstruction from goal via came.

Yield counts fine.

Depth color: for BFS dist; for A* use g. Set sDepth[cur]=g[cur] when done. For frontier cells color by their g too. Store `depthArr` updated at enqueue.

Wave visuals: color = hsl(190 - ... ) Let's compute: t = depth/maxDepth; hue from 205 (blue) → 170? Use `hsl(${200 - 80*t}, 70%, ${30+25*t}%)`. Eh, I'll do hue 215 → 160 with lightness 28→46. Frontier: brighter cyan with slight glow.

OK writing now. Also grid background, outer wall.

Legend: Start, Finish, Carving (generation colors: unvisited/in-stack/head/backtracked), Explored, Frontier, Solution path. Maybe group.

Let's produce the code.

Also handle window resize for canvas CSS scaling — canvas has fixed internal size, CSS max-width:100%, height auto. Fine.

Let me write the file now.

I need to be careful with the render loop and the "path" glow line.

Full render:

```js
function render(){
  ctx.clearRect(0,0,cw,ch);
  // board bg
  // cell fills
  for each cell: fillRect with color
  // path polyline (if mode path/done): through revealed cells
  // walls
  // start/finish markers
  // head marker (current cell) small square
}
```

Draw start/finish markers as circles with label "S"/"F"? Let's draw filled rounded squares with distinct colors, always on top of fills but under path? Path passes through them. Draw order: fills, path line, walls, markers.

Now text for status: mode + step counts.

Write.

Regarding "animate generation so carving progress is visible": show the current stack trail as connected colored line? Draw a polyline through the current stack (from start to head) in magenta — very nice visualization of carving path. Store `stack` array in state and draw it. That's a great visual. Let's do that: draw stack polyline with alpha, plus head dot.

But the stack includes cells that are on current branch; backtracked cells leave the stack — good visualization.

I'll keep `gStack` array reference updated by the generator (it mutates the same array). Draw polyline through gStack centers.

OK, write the code.

Time check: fine. Let me write.

For speed slider: `<input type=range min=1 max=40 value=6>` labeled "Speed".

Now writing the whole file.

```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>Maze Generator & Solver</title>
<style>...</style>
</head>
<body>
<header>...</header>
<main>
 <section class="panel">
   <div class="controls">
     <button id="btnNew">New Maze</button>
     <button id="btnReplay" disabled>Replay Solver</button>
     <label>Algorithm <select id="algo"><option value="bfs">BFS</option><option value="astar">A*</option></select></label>
     <label>Speed <input id="speed" type="range" min="1" max="40" value="7"><span id="speedVal">7</span></label>
     <button id="btnPause">Pause</button>
   </div>
   <div class="stage"><canvas id="cv"></canvas></div>
   <div class="status"><span id="statusText"></span><span id="verifyText"></span></div>
 </section>
 <aside class="side">
   <h2>Legend</h2>
   <ul class="legend">...</ul>
   <h2>Stats</h2>
   <dl id="stats">...</dl>
   <p class="hint">How it works...</p>
 </aside>
</main>
<script>...</script>
</body>
</html>
```

Let me write actual content now.

Stats: Cells carved, Generation steps, Solved steps/Explored cells, Path length, Path efficiency (path/explored).

Write the code with care to avoid bugs.

Let me write out final JS.

```js
const COLS=25, ROWS=15, N=COLS*ROWS;
const CS=34, PAD=18;
const cv=document.getElementById('cv');
const ctx=cv.getContext('2d');
const DPR=Math.min(window.devicePixelRatio||1,2);
const CW=COLS*CS+PAD*2, CH=ROWS*CS+PAD*2;
cv.width=CW*DPR; cv.height=CH*DPR; cv.style.width=CW+'px'; // but responsive CSS overrides with max-width
ctx.setTransform(DPR,0,0,DPR,0,0);
```

If CSS sets max-width:100%, style.width px overridden by CSS rule `#cv{max-width:100%;height:auto}`. Setting inline style width may conflict; I'll rely on CSS: `canvas{width:100%;max-width:${CW}px;aspect-ratio:CW/CH;height:auto}`. Simpler: CSS class with width:100%; height:auto and the intrinsic aspect from attributes. Just set attributes width/height (device px) and CSS max-width:100%; height:auto → intrinsic ratio preserved. Good, skip inline style.

Walls bitmask: N=1,E=2,S=4,W=8. Neighbors dir deltas with wall bits:
```
const DIRS=[{dx:0,dy:-1,w:1,opp:4},{dx:1,dy:0,w:2,opp:8},{dx:0,dy:1,w:4,opp:1},{dx:-1,dy:0,w:8,opp:2}];
```

wall array `walls=Uint8Array(N)` init all 15.

carve(a,b): walls[a]&=~d.w; walls[b]&=~d.opp.

hasWall(a,b) check.

openNeighbors(i): iterate DIRS, check !(walls[i]&d.w) and bounds.

Generation init:
```
function resetMaze(){
  walls.fill(15);
  gState=new Uint8Array(N); //0 unseen,1 in stack,2 done
  gStack.length=0 ...
}
```

Generator:
```
function* generate(){
  let i=0; gState[i]=1; gStack=[i]; genHead=i;
  yield {t:'init'};
  while(gStack.length){
    const cur=gStack[gStack.length-1];
    genHead=cur;
    const cands=[];
    for(const d of DIRS){ const nx=... ; if(!in bounds) continue; const j=...; if(gState[j]===0) cands.push([j,d.w]); }
    if(cands.length){
      const [j,w]=cands[rand];
      walls[cur]&=~w; walls[j]&=~opposite(w);
      gState[j]=1; gStack.push(j); genSteps++; carved++;
      yield;
    } else {
      gState[cur]=2; gStack.pop(); genSteps++;
      yield;
    }
  }
}
```
Need `opposite` map: 1↔4, 2↔8.

Note: when the stack becomes empty, genHead = -1.

Draw generator stack polyline: through gStack.

Solver state arrays:
```
let sState=new Uint8Array(N), sDepth=new Int32Array(N), came=new Int32Array(N), sCur=-1;
```

Let me write the solver as a factory returning generator based on algo.

Then path state: `path=[]`, `reveal=0`.

advance():
```
switch(mode){
 case 'gen': {
   const r=genIter.next();
   if(r.done){ onGenDone(); }
   return true;
 }
 case 'search': {
   const r=solIter.next();
   if(r.done){ onSearchDone(); }
   return true;
 }
 case 'path': reveal++; if(reveal>=path.length){reveal=path.length; mode='done'; updateStatus();} return true;
 default: return false;
}
```
For 'path' mode we want reveal to progress with a delay: each call increments by 1; with spf=7 that's fast but path is short so fine.

Loop:
```
function loop(){
  raf=requestAnimationFrame(loop);
  if(!paused){
    const spf=+speed.value;
    let guard=spf;
    while(guard-- > 0 && !advance()) break;
    render();
    updateHud();
  }
  if(mode==='done'){ stopLoop(); render(); }
}
```
Careful: `while(guard-->0 && advance())` — advance returns false only when mode==='done'. But mode 'gen' returns true even on final transition; that's fine (next call goes to 'search'/'path').

Hmm when mode==='done' at entry, advance returns false and loop stops.

startLoop(){ if(!raf) raf=requestAnimationFrame(loop) }.

New maze:
```
function newMaze(){
  stopLoop(); // cancel previous animation
  resetMaze(); resetSolver();
  mode='gen'; paused=false; ... startLoop();
}
```

Replay solver: requires mode not 'gen' running... If generation still in progress, disable button. Enable after generation done. If solver currently running, restart solver on same maze (cancel animation of solver, keep walls). Requirement: "New Maze cancels the previous animation and generates a fresh maze; Replay Solver uses the existing maze without changing its walls."

replaySolver(){ stopLoop(); resetSolver(); mode='search'; solIter=solver(algo); startLoop(); }

Also changing select triggers replaySolver if maze ready.

Also, when generation is running and user clicks New Maze again: fine.

Now render function.

```js
function render(){
  ctx.save();
  ctx.clearRect(0,0,CW,CH);
  // panel bg
  roundRect fill
  // cells
  for(let y=0;y<ROWS;y++)for(let x=0;x<COLS;x++){
    const i=y*COLS+x; const px=PAD+x*CS, py=PAD+y*CS;
    ctx.fillStyle=fillFor(i);
    ctx.fillRect(px+1,py+1,CS-2,CS-2);
  }
  // gen stack trail
  // search frontier? included in fills
  // path
  // walls
  // markers
  ctx.restore();
}
```

fillFor(i):
```
if(mode==='gen'){
  if(i===genHead) return COL.head;
  const st=gState[i];
  if(st===1) return COL.trail; if(st===2) return COL.carved; return COL.unseen;
}
// solver modes
if(i===0) return COL.startBase; if(i===N-1) return COL.finishBase;
if(mode==='path'||mode==='done'){ if(i<... ) }
```
For path mode, path cells up to reveal get gold (unless start/finish which get special but tinted). Let's compute: pathSet with index positions. `posInPath` Int32Array init -1.

fillFor solver:
```
const ppos = posInPath[i];
if(ppos>=0 && ppos < reveal) return COL.path;
if(sState[i]===2) return exploredColor(sDepth[i]);
if(sState[i]===1) return COL.frontier;
return COL.carved(unseen maze floor)
```
And start/finish override: draw markers on top anyway, so base fill can be normal; markers will show. Simpler: keep fill as above, then draw start/finish markers on top with strong colors, and when path covers them it's under markers → still distinguishable. Good.

exploredColor(d): precompute palette array of colors for depths (cache by quantized t).

```js
function exploredColor(d){
  const t=Math.min(1,d/Math.max(1,maxDepth));
  const hue=215-70*t, light=26+22*t;
  return `hsl(${hue} 70% ${light}%)`;
}
```

Walls drawing:
```js
ctx.strokeStyle=COL.wall; ctx.lineWidth=3; ctx.lineCap='round';
ctx.beginPath();
for cells: if walls&N → moveTo(px,py) lineTo(px+CS,py); similarly E,S,W... only draw N and W plus E on last col and S on last row to reduce duplicates.
// outer border
ctx.stroke();
```
Outer border: rect stroke.

Head marker: pulsing circle at genHead; sCur during search.

Start/finish markers: rounded squares: start green with glow, finish red/orange. Draw a small ring plus letter.

Path polyline: stroke through centers of path[0..reveal-1] with gold, lineWidth 6, shadowBlur glow. Draw after fills before walls? Walls on top makes it look contained; but path shouldn't cross walls anyway. Draw walls first then path on top? Path over walls looks nicer at crossings... I'll draw path then walls so walls remain crisp, path glow behind. Order: fills, gen trail / path, walls, markers, hud text (no text on canvas besides S/F maybe).

Animation of path: add moving "spark" at head of reveal? Optional: draw a bright dot at last revealed cell. Nice.

HUD update: status text, stats.

Alright, let me write the whole thing and test in the browser.

Also add keyboard shortcuts: N, R, Space (pause).

Let's write the file.

Empty directory. Write index.html.

I left some junk: `--line:#2b3category;` (invalid CSS) and a legend swatch with `background:#2a3category`, plus a leftover dead `tick()` function with a weird while loop. Let me clean those up.

Also `tick` is unused — remove it.

Let me fix these.

Wait, `startLoop` calls `stopLoop` which cancels raf and sets raf=0, then calls tick which sets raf = requestAnimationFrame(tick). That's fine.

But there's a subtlety: in tick, `if (mode === 'done') stopLoop();` — stopLoop cancels the newly scheduled frame. Good.

Also in `advance()` for mode 'path': it changes mode to 'done' and calls finishRun() which calls render() and updateHud(); then tick calls render again — fine.

Potential recursion issue: finishRun → render → ok.

Another: `startSearch` is called from onGenerationDone, which is inside advance inside tick; mode set to 'search', and `if (!raf) startLoop()` — raf is set so no restart. Good.

Now let me run the browser and inspect.

Generation is animating and carving is visible. The visual looks good. Note: the maze walls are drawn as full grid lines everywhere — wait, looking at the image, the walls look like a complete grid (all walls present) even in carved regions. Hmm, actually the carved cells (violet) still show internal walls between them? Let me look closer: in the violet region, there seem to be white lines between cells. That might be because carved cells' shared wall removed but the neighboring unvisited cell still has the wall bit set... no, I clear both sides.

Actually the issue: I only draw N and W walls for each cell, plus E for last column and S for last row. If a wall between cell A (left) and B (right) is removed, then A's E bit is cleared and B's W bit is cleared. A's E isn't drawn (only drawn for last column) and B's W is cleared → not drawn. So it should be open. But the image shows lines inside the violet region... Let me zoom in with a screenshot after generation completes. It might be the pink stack polyline crossing cells, which looks like walls.

Hmm, but the "Carve steps 47 / passages cut 47" vs status "48/375" — consistent (DOM read at different times).

Wait, there's a discrepancy: the top-left region shows carved cells (violet) at (0,0)-(3,0) etc., with a pink line. Looks right.

Let me inspect again after generation completes and solver runs, and also click New Maze mid-animation as required.

Let me take a screenshot now (motion frames would be useful to check animation).

Big problem: the whole board appears orange/gold — the path fill is applied to far more cells than the actual path. Also green cells appear scattered. Wait — the green cells are `exploredColor` at maxDepth (hue 212-66=146 → green). So explored cells look green, not the blue-teal gradient I expected... Actually the gradient goes from hue 212 (blue) to 146 (green) — many explored cells are green. Fine.

But the orange (path color) covers most of the board. Why? `posInPath[i] >= 0 && posInPath[i] < reveal` — posInPath is only set for path cells... unless `resetSolver` isn't clearing? No. Hmm — wait, `path.length` is 183 but there appear to be ~300 orange cells. Actually maybe the orange is the fill for cells where `posInPath[i] >= 0 && posInPath[i] < reveal`. reveal = 183. So only path cells (183) get orange. But the image shows way more than 183 orange cells out of 375... Let me count roughly: it looks like ~60% of the board is orange. That's ~225 cells. Hmm, hard to tell; the path is 183 cells and meanders, so it could plausibly look like that much coverage. Actually a 183-cell path in a 375-cell maze is 49% of cells. Looking at the image, orange fraction seems maybe 55-60%. Plausible-ish given the path meanders and fills regions.

But wait — the path should be a simple connected polyline. In the image, orange regions look like big blobs, not a 1-cell-wide snake. E.g., bottom-left is green, top area has large orange blocks 2-3 cells wide. Hmm, at the top there's a solid orange band across many columns with green cells below — a snake could look like that.

Let me verify programmatically instead of by eye: check path connectivity via console evaluation. Better: run a check in the page — but I can't evaluate JS directly with these tools... I only have screenshot/inspect/DOM. The status line already says "path verified: 183 cells, wall crossings 0, no repeated cells" which is computed by verifyPath, which checks adjacency and open passage for every consecutive pair. That's strong evidence the path is correct.

So the orange is likely correct — a 183-cell snake that fills much of the board. But the walls: I notice the path crosses through places where walls seem present... The white grid lines: within orange areas there are white lines separating adjacent orange cells — but consecutive path cells have no wall. Hmm, looking at the image, in the orange regions there are white lines between some adjacent orange cells, which would be wrong... unless those adjacent orange cells are not consecutive in the path (path passes near itself, with a wall between — legit in a perfect maze).

OK. But there's a real visual problem: the path fill color makes it hard to distinguish the actual solution polyline from explored cells, and the whole thing looks noisy. Also the drawn gold polyline (lineWidth 7) is barely visible because cells are also gold.

Improvements:
1. Don't fill path cells gold; instead keep explored/base fill and draw the gold polyline on top (that's the "highlight"). Or fill path cells a darker amber so the polyline reads. I'll fill path cells with a subtle darker tone and rely on the polyline.
2. Explored color gradient: currently ends in green which collides with the Start marker color. Change the gradient to blue→violet (hue 220 → 265) or blue→cyan, keeping green exclusively for Start. Let's use hue from 205 to 250 with lightness 30→48. Frontier = cyan bright.
3. Wall color: white walls on light fills is fine, but on gold it's washed. Keep.

Also, the path polyline is drawn before walls, so walls overlay it — good.

Another issue: the maze walls look too "busy"/uniformly gridded — hard to see open passages. In the earlier generation screenshot, the carved region still looked like a full grid. Let me zoom to verify wall carving is visually clear. The requirement says "Draw cell walls clearly and animate generation so carving progress is visible." Let me check the actual maze structure by taking a screenshot mid-generation at slower speed, and visually confirm open passages.

Concern: In the first screenshot, the violet region appeared as blocks with white lines between every cell. If walls between carved adjacent cells (parent-child) were removed, we'd see open connections. The violet cells shown were mostly non-consecutive (stack trail meanders), so many shared walls remain. Plausible. But in the solved screenshot, along the gold path, consecutive cells should have no white line between them. Looking at the image... e.g., the top row from left: cells at (0,0) area, I see white vertical lines between orange cells in the top band. Hmm, some gaps do appear open.

Let me do a targeted visual test: set speed to 1, click New Maze, screenshot mid-generation to inspect carving closely. Actually better: I can verify walls programmatically by writing a small node test replicating the algorithm? That's overkill.

Alternative: Add a temporary debug readout? The verifyPath already proves adjacency + open passage for the whole path, computed in-page. That's the authoritative check. The visual question is whether walls render correctly. Let me look at a zoomed screenshot region... The browser tool screenshots the full page only. I can temporarily make the canvas render bigger? Or check by looking at the generation phase screenshot with speed=1 so few cells carved, making structure clear.

Let me first improve colors, then do a slow-generation visual check and the New Maze mid-animation check.

Also one more potential bug: `fillFor` for path cells excludes START and GOAL, so their fills show explored/frontier color under the markers — fine.

Another: after `finishRun`, `btnPause.disabled = true` but Pause stays as "Pause". Fine. But when replaying, `replaySolver` sets btnPause.disabled=false. Good.

Also `posInPath` persists after a new search? resetSolver creates new arrays. Good.

Let me also reduce path fill to a translucent amber so the polyline stands out, and change explored gradient to blue→indigo.

Additionally, I should make the frontier color distinct from explored: cyan #5fe3ff is close to blue-indigo explored — fine.

Let me edit.

Now reload and check. Also test: click New Maze while animation active, and slow-speed inspection of carving.

Let me set speed to a low value first for inspection. The speed slider is at (95,168) to (213,168) roughly. Value 8 currently. Let me instead just reload and screenshot at various times.

Plan:
1. reload → screenshot (generation mid).
2. Wait for solve → screenshot.
3. Click New Maze mid-solve → screenshot to confirm clean replacement.
4. Test A* selection → replay.

Let me reload and inspect quickly.

Now I can clearly see the carving: violet trail cells with the pink stack polyline, magenta head. BUT: I notice white lines still between consecutive trail cells! Look at the trail: from start going right along the top row, there are vertical white lines between each violet cell. That means walls are NOT being removed visually — a bug!

Wait, the pink polyline crosses them. Let me look carefully at the top band: cells (0,0) through (7,0) violet, and I see white vertical separators between them. That's wrong — carved passage should have no wall.

Hmm, why? Let me check the wall-drawing logic:

```
if (w & 1) { top }
if (w & 8) { left }
if ((w & 2) && (i % COLS === COLS - 1)) { right for last col }
if ((w & 4) && (i >= N - COLS)) { bottom for last row }
```

For a horizontal wall between cell i and i+1: cell i's E bit (2) and cell i+1's W bit (8). I only draw E for the last column, so if cell i's E is still set (not carved) it's invisible in the drawing... wait no. If the wall between i and i+1 still exists, cell i+1's W bit is set → I draw the left edge of i+1 → correct. If carved, both cleared → no line. So the logic is right.

So why do I see lines between consecutive violet cells? Because the violet cells are the *stack trail*, which is a path — consecutive stack cells ARE connected by carved walls. Hmm, unless the visible lines are the pink polyline segments crossing... The polyline goes through centers, so at a vertical line position... no, the polyline is pink.

Let me look again more carefully at the image. Top row: I see violet cells separated by thin white vertical lines. Actually maybe those are the *unvisited* neighbors' left walls? No, a wall line is shared.

Wait — maybe the issue is that the trail isn't only the stack: gState===1 for stack cells, gState===2 for finished. In the image, the top row is violet (in stack) and there's a branch going down at column ~7. All violet = on stack = connected in order... but the stack order is: start → ... The stack is a path from start to head, so consecutive stack cells are adjacent AND carved. So no wall between them.

Unless... the drawing has a subtle bug: after `ctx.beginPath()` inside the loop, I stroke once at the end — fine.

Hmm, let me check `walls[cur] &= ~pick.w` — `pick.w` is the direction bit from cur toward j. And `walls[pick.j] &= ~pick.opp`. In the generator, I build cands with `{ j, w: d.w, opp: d.opp }` — yes both present.

So walls should be cleared. Let me zoom in to be sure — maybe what I'm seeing is the cell fill gap: I fill `cx(i)+1, cy(i)+1, CS-2, CS-2`, leaving a 1px gap of board background between cells — which appears as a thin dark line, not white. But at the screenshot scale, the grid lines look white/light because walls are drawn at 2.6px.

Let me count: the image is 1200x800 scaled from viewport 1200x800, canvas CSS width ~816px for 850 internal → nearly 1:1. So white lines = walls.

Hmm, look at the region around (2,1)-(3,1) violet block: there's a white horizontal line under the top row? The top row violet cells at row 0 and violet at row 1 col 2-3... 

I need a closer look. Let me use the motion/screenshot at a moment when only a few cells are carved, or better: temporarily reduce visual noise by checking a specific pair programmatically. I can't eval JS via the browser tool... but I CAN replicate the algorithm in Node and print an ASCII maze to confirm wall carving logic. That verifies the algorithm, not the rendering.

Actually, wait. Let me reconsider the render: I draw walls for cell i using `walls[i]`, but I only draw N and W per cell. Consider the wall between a carved pair where the *child* is above the parent... it's symmetric, both bits cleared. Fine.

Let me look at the screenshot once more, specifically at the pink polyline: it goes right along the top, then down at column 7, then... The white lines between the top-row violet cells — hmm, actually maybe those white lines are at the *bottom* of the top row cells (i.e., the S wall of row-0 cells, which is legitimate since row 1 is unvisited there). At this resolution, a vertical line between two adjacent cells and a horizontal line below them are distinguishable... I see a clear grid pattern in the violet band, suggesting both.

Let me just get a bigger view: I'll temporarily set the canvas CSS to a larger size? Instead, use the browser `motion` action to get frames — same scale.

Better idea: run the same generator logic in Node and print ASCII. If carving is correct there, the issue is purely my reading of the screenshot. But a rendering bug is possible: e.g., `roundRect` outer border stroke with lineWidth 3.4 draws only the border — fine.

Hmm, one real suspect: `ctx.strokeStyle = C.wall; ctx.lineWidth = 2.6;` then `beginPath` and lots of moveTo/lineTo, then a single `stroke()`. With `lineCap='round'`, overlapping segments are fine.

Let me do the Node ASCII check — quick and authoritative for the algorithm. And for rendering, I'll add a temporary debug: draw carved openings? No.

Alternative approach to visually confirm: slow down (speed=1) and take a screenshot when only ~10 cells are carved in a straight line. Then the structure is unambiguous. Let me set the range input to min value via drag... The tool supports `drag`. Or I could click on the left end of the slider track to decrease value. Slider spans x 95→213 for values 1→40. Value 8 is at x≈116. To set value 1, click at x=95. Let me drag the thumb to x=96.

Actually simpler: reload the page and screenshot immediately — the first frame after reload showed 23-63 cells already (screenshot happens after some time). Hmm.

Let me do the drag to speed=1, then click New Maze, then screenshot.

Also, I realize I should double check: is it possible that the visible white lines inside the violet band are correct because the band isn't a single trail? gState===1 means "on stack" — the stack is a simple path, so it is a connected trail. And gState===2 (finished/backtracked) cells are colored C.carved = #243257 (dark navy), similar to unseen #1a2440. So violet = current stack only. Connected. So walls between consecutive violet cells MUST be open.

Unless... the fill colors: C.trail #7b6bff violet vs C.carved #243257. In the image the violet band is continuous from (0,0) rightward, then down. Yes that's the stack.

So if white lines appear between them, it's a rendering bug. Let me verify with Node + a headless canvas? Not available.

Let me just do the close-up inspection via drag to slow speed.

Now the solved view is much clearer: the gold polyline snakes through open passages, and I can confirm walls are removed where the path passes (the polyline crosses grid lines at open spots). 

However — I notice a rendering issue: the maze walls look like a nearly-complete grid in the dark (unexplored) regions. Look at the right half: it's a full grid of white lines with almost no openings, whereas the maze must have 374 openings. Hmm, in the unexplored (dark) region, walls are drawn between every cell? That can't be right for a solved maze — BFS with 220 explored cells means 155 cells unexplored, and those unexplored cells still have all 4 walls drawn?? No — walls array is per-cell; a carved opening clears both cells' bits, so an opening between an explored and unexplored cell would render open. But between two unexplored cells that ARE connected (carved earlier), the opening should also render.

Wait, look at the left region: violet cells (trail color!) — that's odd. After generation, mode is 'search'/'path'/'done', so fillFor uses solver colors. Violet #7b6bff shouldn't appear... unless exploredColor(0) = hsl(206,58%,25%) = dark blue. Hmm, the bright violet/blue blocks on the left are `hsl(252, 70%, 42%)`-ish. That's hue 206+46 = 252 at t=1 → blue-violet! Yes: exploredColor at max depth = hue 252, sat 70, light 42% → a vivid violet-blue. That matches. Good — those are the deepest explored cells.

So the left side is fully explored (deep shades), right side unexplored dark navy. Makes sense for BFS from start with 220/375 explored before hitting goal.

Now the walls question: on the right (unexplored) side, the grid looks almost entirely closed. Let me check: in a perfect maze, the unexplored region is a connected subtree; openings exist within it. Looking at the image right side, I do see some missing lines (e.g., around (19,4)-(20,4) merges). It's plausible but visually the white wall grid is dense. Actually here's the thing: since the frontier cells (cyan) appear only near the goal, the unexplored region's internal openings should be visible. I see a few, e.g. around x=770-800,y=280 there's a merged pair. OK, seems right.

Hmm, but wait — there's a subtle bug in the wall drawing! I draw N and W for every cell, but for E I only draw when `i % COLS === COLS-1` (last column) and for S only when `i >= N - COLS` (last row). That's correct for avoiding duplicates: internal vertical wall between col k and k+1 is drawn as the W wall of the cell at col k+1. Internal horizontal wall between row r and r+1 is drawn as the N wall of the cell at row r+1. ✓.

So the rendering is correct. 

Now, the earlier concern about white lines between violet trail cells: in this screenshot the path polyline crosses grid lines cleanly at openings. Let me look at the top-left: the path goes right along row 0 from (0,0) to (7,0)... I see the gold line crossing vertical white lines? At the top band, between the two gold horizontal segments there appear to be white vertical lines crossing the gold. Hmm, at the top row (y≈228), the gold horizontal band from x≈75 to x≈390 — I see white vertical ticks at intervals? Looking closely at the image, the top gold band appears continuous with white vertical lines only at the boundary where the path turns. Honestly the gold is drawn *under* the walls, so any remaining wall would show as a white line over the gold. I can see some short white vertical marks inside the gold band at x≈140, 200, 260, 320... 

Hmm! That's concerning. But verifyPath says wall crossings 0. verifyPath checks `openPassage(a,b)` using the same `walls` array used for rendering. If verifyPath passes, the walls bits ARE cleared, so the render must not draw them... unless the drawn line comes from a *different* cell's bit that wasn't cleared!

AH — that's it. Bug: `openPassage(a,b)` checks `neighborCells(a)` which tests `!(walls[a] & d.w)` — only one side. If the two sides got out of sync (one cleared, the other not), verification would pass while the render (using the neighbor's W bit) draws a wall.

Do the bits get out of sync? In the generator I clear both: `walls[cur] &= ~pick.w; walls[pick.j] &= ~pick.opp;`. That's symmetric. So they can't diverge... unless `pick.opp` is undefined! In generate(), cands push `{ j, w: d.w, opp: d.opp }` — d.opp exists. OK.

Hmm, so what are those white marks in the gold band? They might be the *N/S* walls of adjacent rows bleeding at this scale, or the cell fill gaps (1px dark) — no, those are dark.

Let me look at the actual pixel evidence differently: take a screenshot while paused mid-generation at speed 1 so only a handful of cells are carved. Then a straight 2-cell trail would show unambiguously whether the shared wall disappears.

Let me click New Maze now (speed 1) and screenshot right away — with speed 1, after ~1 second only ~60 cells carved. Actually the screenshot is taken immediately after the click, so maybe only ~10-30 cells carved. Let's do it. This also tests "request New Maze while animation is active" (the previous run just finished, so let me instead click New Maze during solving).

Plan: click New Maze (starts gen at speed 1), screenshot immediately → inspect early carving.

Now this is a clear bug demonstration. Only 4-7 cells carved: (0,0) start, (1,0) trail, (2,0) head, and (2,1) trail. But I can see white wall lines BETWEEN these cells:
- Between (0,0) and (1,0): there's a vertical white line at x≈87? Looking at the image, the top-left cells: green S at x 60-85, violet at 87-110, pink at 113-140. There IS a gap/line between them.
- Between (2,0) pink and (2,1) violet below: a horizontal white line at y≈246 clearly separates them.

So the carved openings are NOT being rendered as open. Yet `verifyMazeIsPerfect` reported edges=374 and count=375 using `neighborCells` which checks `!(walls[i] & d.w)` for each direction from cell i... 

Hold on: if only ONE side's bit were cleared, then neighborCells(a) would find b but neighborCells(b) wouldn't find a. My edge count loop: `for i, for n of neighborCells(i), if (n.j > i) edges++` — asymmetric clearing would give edges = 374 still if the cleared side is always the lower index... Hmm, and BFS reachability uses neighborCells(cur) → finds j even if j's bit isn't cleared, so count=375. So verification would pass even with one-sided clearing! That's a real possibility.

Where could one-sided clearing happen? `walls[cur] &= ~pick.w; walls[pick.j] &= ~pick.opp;` — both cleared. Unless... `pick.opp` — I set `cands.push({ j, w: d.w, opp: d.opp })`. Yes.

Hmm wait, but is the wall actually there or am I misreading the render? The cell fills are inset by 1px (`cx(i)+1, CS-2`), leaving a 2px gap of dark board between cells. The wall stroke is 2.6px centered on the grid line. So an OPEN passage would show a 2px dark seam between fills — which at this scale could look like a line! Look at the pink (2,0) and violet (2,1): there's a distinct white horizontal line at y≈246 which is much brighter/thicker than the dark seam. Compare to a known-open pair... hmm, I can't compare.

Let me test differently: I'll add a temporary debug overlay? Better: use the console. I can't eval JS directly... but maybe I can make the page itself log the wall state. Cleverer: I'll write a small Node script that replicates the exact generator + wall-drawing decisions and prints an ASCII maze. That definitively tests the algorithm's wall clearing and my drawing rule (N/W + last-col E + last-row S). If ASCII shows a proper maze, then the render rule is right and the issue is just the 1px fill seam being overdrawn... 

Wait, actually! I bet I know the bug. Look at the render: the walls are drawn with `ctx.strokeStyle = C.wall` = '#dce7ff' — nearly white — and lineWidth 2.6. But look at the *outer border*: I stroke roundRect(PAD,PAD,...) with lineWidth 3.4. Fine.

Hmm, but here's a thought: is `walls` being read correctly? `walls = new Uint8Array(N).fill(15)` — Uint8Array.prototype.fill exists. ✓

Let me check `neighborCells`: `if (!(walls[i] & d.w)) out.push(...)`. ✓

OK let me just do the ASCII test in Node — it's fast and definitive about the algorithm. Then, for the rendering, I'll eliminate the 1px seam ambiguity by filling cells edge-to-edge (no inset) so open passages are unambiguously continuous, and add a subtle floor grid only for unseen cells.

Actually — hmm, wait. I see it now! In the screenshot, between the green start cell and the violet cell there IS a white line, but is that white line the *bottom* wall of the top row (S of (0,0) drawn as N of (0,1))? The line I'm seeing at y≈246 spanning x 113-140 separates pink (2,0) from violet (2,1). If the wall between them were carved, we'd see the fill colors continuous except a 2px dark seam.

I need certainty. Let me do the Node ASCII replication.

The algorithm is correct: 0 asymmetric bits, exactly 374 openings, and the ASCII shows a proper maze with open passages (e.g., "|   |" gaps).

So the wall data is right. The canvas render must be showing the openings, but the 1px inset fill gap + antialiasing makes it look closed at small scale? Let me re-examine the last screenshot: the pink head cell (2,0) and violet (2,1) — I claimed a white line between them. Let me get a zoomed look. I can't zoom the browser tool... but I CAN temporarily increase cell size? No — better: I can add a debug "open passage" rendering? 

Alternative: check via a different visual signal. In the ASCII, openings exist. In the canvas, openings are drawn by omitting the line. Since the data is symmetric and correct, the canvas MUST show openings. The apparent lines are likely the 2px dark seam between inset fills, which at 1:1 scale with a bright wall grid around them reads as a wall.

Hmm, but the seam is dark (#0a0f1e board) vs wall #dce7ff white. In the screenshot at y≈246 between pink and violet, the line looked whitish... Actually, looking again at that screenshot: the pink cell (2,0) is at approx x 113-140, y 228-244; the violet cell below at y 248-264. Between them at y≈246 there's a horizontal line. Its color in the image — I described it as white; the surrounding grid lines are white too. Given the ambiguity, let me eliminate it entirely: draw cell floors edge-to-edge (no 1px inset), and instead of relying on absence of wall lines, ALSO draw open passages as a lighter "floor seam"? No — cleanest fix: make walls thicker (3px) and floors flush. Then an opening is unambiguously continuous floor.

Actually, better idea for clarity: draw the walls in two layers — a faint "full grid" underlay (so the maze reads as a grid) plus bright actual walls. Hmm, that could confuse too.

Decision: fill floors flush (inset 0), keep wall lineWidth 3 with a subtle dark outline (shadow) so walls pop and openings read clearly. Also add a light "passage" indicator: for each carved opening, draw a small bright notch? Not needed if floors are flush.

Let me make these changes:
1. `ctx.fillRect(cx(i), cy(i), CS, CS)` — flush.
2. Walls: draw a dark casing stroke first (lineWidth 5, color #0b1020) then the light stroke (lineWidth 2.8) — gives crisp contrast, and openings show continuous floor.
3. Keep outer border.

Then re-inspect at speed 1 with a few cells carved.

Also, I want a definitive in-page check of what's rendered. I could add a tiny self-test that logs to console: e.g., after generation, log a sample of adjacent carved pairs and confirm both bits cleared. The Node sim already proves the data. The remaining risk is purely visual, which the flush-fill change addresses.

Let me also double check the "New Maze while animation active" behavior — in the click test, New Maze during 'done' worked. I need to click New Maze *during* generation/solving and confirm clean replacement (no leftover path fills). Since newMaze() calls resetSolver() and mode='gen', fills use gen branch. Good. I'll test it mid-search.

Let me apply the render changes.

Also the path polyline is drawn before walls — with the dark casing at 5.4px, the gold path (13px halo + 6px core) crossing openings will be partly covered by the casing at wall lines? The path only crosses openings, so no wall there. Good.

Now reload and check the early carving again.

Now the openings are clearly visible: the violet trail forms a continuous corridor — e.g., at the top, cells (0,0)→(3,0) area show a merged violet block with no white line between them, and the pink polyline flows through. Look at the region x 60-200, y 228-265: violet shapes merge into corridors. Yes! Now the carving reads correctly.

Now let's let it finish and check the solver + path, and test New Maze mid-search.

Let me take a screenshot after a moment (motion action gives frames over time). Let me use `motion` to capture a few frames of the solver animation.

The solved view looks great: corridors visible, gold path snaking through open passages, explored shading, frontier cyan cells near the goal.

One observation: the path is 197 of 375 cells — a long snake. It clearly follows corridors. The gold path passes through openings only — visually confirmed (e.g., the gold turns at cell centers and crosses grid lines only where walls are absent... I see gold crossing where the white wall line is absent).

Hmm, one thing: the explored color is quite saturated violet/blue and competes with the trail color. Fine.

Also the path-fill (dim amber #6a4a12) is visible as darker amber cells under the bright line — good, distinguishable.

Now test the required interaction: click New Maze while animation is active (during search), and verify clean replacement. And test Replay Solver (walls unchanged) + A* switch.

Let me click New Maze, then immediately click New Maze again mid-generation (to test cancel), then screenshot.

Actually the key check: "request New Maze while animation is active. Check that the new generation replaces the previous view cleanly." Let me click New Maze during the search phase. To catch it mid-search, click New Maze (generation takes ~1.5s at speed 8) then click New Maze again quickly. Two separate tool calls happen sequentially with some delay; the generation at speed 8 takes 749/8 ≈ 94 frames ≈ 1.5s, then search ~350/8 = 44 frames ≈ 0.7s, path reveal fast. Total ~2.5s. So clicking New Maze twice in a row (separate calls, each maybe ~100ms apart in wall-clock? probably more) should land mid-animation.

Let me do: click New Maze → immediately click New Maze (second call) → screenshot. Then check DOM shows GENERATING with low step counts and no stale path.

Also test Replay Solver with A* selected: change select to astar (which triggers replay), screenshot mid-search.

Let me do the double New Maze first.

Fresh generation started cleanly: stats reset (search steps 0, path length —), no leftover gold, Replay Solver disabled again. 

Note the DOM readout showed "Carving… 56/375" while the screenshot shows 24/375 — the DOM snapshot is taken at a slightly later time than the screenshot? Whatever, both consistent with an active animation.

Now: click New Maze AGAIN while this generation is mid-flight (to test cancel during generation, not just after done). Then also test the solver-mid-search cancel. Let me click New Maze twice more quickly and screenshot.

Then test A* + Replay Solver.

Let me do: click New Maze (cancel mid-gen) → then immediately click New Maze again? Each tool call is sequential. Let me click New Maze now (mid-generation) and screenshot to confirm it restarts cleanly (carve steps back to low, no artifacts).

Mid-generation cancel works: a fresh maze (different shape), carve steps restarted at 0 and now at 23, no leftover from the previous run. The console shows two "maze verified" logs from the two *completed* generations earlier (the first run and the run that completed before). Wait — the second New Maze click happened while generating, so that generation never completed; the two logs correspond to the two completed mazes. Good, no runaway loops: exactly one log per completed generation.

Hmm, important: I should verify the cancelled generator's rAF loop is truly dead (no double-speed stepping). Evidence: carve steps advanced from ~0 to 23 in the time between the click and the readout — consistent with a single loop at speed 8. If two loops were running, we'd see double. Also `stopLoop()` cancels raf before starting a new one, and startLoop calls stopLoop first. Fine.

Now test A* + Replay Solver. Let me change the algorithm select to A* — that triggers replaySolver only if mazeReady (currently generating, so not ready). Better: wait for solve, then switch to A*.

Let me take a motion capture to reach the solved state, then change select to A*, then screenshot mid-search to verify A* exploration and that walls are unchanged (compare maze shape? I can verify by checking the status/verify text and that the maze looks identical).

Actually a stronger check for "Replay Solver uses the existing maze without changing its walls": capture the solved BFS maze screenshot, click Replay Solver, and confirm the final path is identical (same maze, same algorithm → same path since unique path). If walls changed, the path would differ. Good test.

Let me first let it finish (motion), then click Replay Solver and compare.

Solved, path verified 181 cells, 0 wall crossings.

I notice a visual issue: there's a violet (C.trail #7b6bff) column near the top-right (x≈760, y≈250-410) and violet cells scattered. Those are exploredColor at t=1 → hue 252 = violet-blue. OK, that's the deepest explored shade, not a bug. But it's confusingly similar to the "Active carve trail" legend swatch (#7b6bff). Let me cap the explored hue range so it doesn't reach 252: use hue 200 → 235 and lower saturation at the top end. Let me change to `hsl(200 + 30t, 55+10t%, 24+16t%)` → max hue 230 (blue), clearly distinct from violet #7b6bff (hue ~248) and from frontier cyan.

Hmm, 230 vs 248 is still close-ish. Let's instead go the other direction: explored from deep teal-blue (hue 195) to lighter blue (hue 215) with rising lightness, so depth reads as brightness rather than hue. That's clearly distinct from violet trail and from green start.

exploredColor: hue = 200, sat = 55 + 20t, light = 22 + 30t → dark navy-teal (near start) → bright blue (far). Combined with frontier cyan #5fe3ff, still distinguishable (frontier is much lighter/saturated cyan).

Hmm, but then "explored near start" (dark) looks like unexplored floor (#243257). Let me flip: bright near start, fading darker with distance? The wave reading is better if newer = brighter. Alternative: keep lightness increasing with depth but start above the floor color: light 32 → 58, hue 190 → 215. Floor carved #243257 has lightness ~24%. So explored cells (32-58%) are clearly brighter. Good.

Let me set: `hsl(${188 + 34*t} ${60 + 15*t}% ${32 + 24*t}%)`.

Also update the legend swatch gradient to match (#1e6a78 → #4b7fd6-ish). Let me compute endpoints: t=0: hsl(188,60%,32%) ≈ #21737f... roughly teal. t=1: hsl(222,75%,56%) ≈ #4d7ce8-ish blue. Legend gradient: linear-gradient(90deg,#21737f,#4d7ce8).

Also the "Path cell" dim amber #6a4a12 works.

Let me also double check one thing in the last screenshot: near top-left, the path goes from S rightwards along row 0 — and the gold band at the top spans the full width to x≈400. Looks fine.

Another check: the frontier cyan cell at top-right (x≈790,y≈222) is adjacent to the finish area? BFS stopped when it dequeued GOAL... wait, the goal is bottom-right; the frontier cell is top-right. Hmm, that means the search ended when `cur === GOAL` was dequeued, and remaining frontier cells stay cyan. But a cyan cell at top-right far from goal — that's just a leftover queued cell (BFS marks cells as frontier when enqueued; when the loop returns early at GOAL, some cells remain in state 1). Fine and honest.

But wait — there's a subtle issue with BFS: I `return` when `cur === GOAL` is dequeued. Since BFS marks visited at enqueue time and cameFrom is set then, the path is optimal. ✓

For A*: I return when cur === GOAL is popped. ✓

Now let me apply the explored-color fix and then test A* + Replay Solver.

Now reload, let it solve with BFS (capture the maze shape), then click Replay Solver and confirm the same maze + same path (walls unchanged), then switch to A*.

Sequence:
1. reload → motion (to solved)
2. click Replay Solver → motion (should show same maze, path re-animated)
3. change algo select to A* → screenshot mid-search.

Let me do reload + motion.

Good. Now let it solve, then test Replay Solver.

I'll click Pause to freeze? No — let me use motion to reach solved state.

Now the explored shading reads as a blue wave distinct from the violet trail. Path verified 109 cells, 0 crossings. The maze corridors are clearly visible now.

Now test Replay Solver on this same maze (walls must be unchanged → same path 109 cells), and then A*.

Click Replay Solver at (211,128).

Replay Solver works: same maze walls (identical to the previous screenshot's wall layout), BFS restarting from the start with the wave. The exploration follows open passages — visible teal/blue corridor hugging the left wall, with the frontier cyan cells at the edge. 

One nit: the stale "✓ path verified: 109 cells..." verification text persists during the replay. It should clear when a new search starts (it's the previous run's claim). Actually it's fine as a maze-level statement, but better to clear it on search start and re-verify at the end. Also "Path length —" resets correctly.

Also I notice the frontier wave at 24 cells explored only covers a corridor going down the left side — that's BFS following open passages. ✓

Let me fix the stale verify text: in startSearch(), clear verifyEl (or set to the maze-perfect statement). I'll store the maze verification string and re-display it, replacing the path claim.

Let me implement: keep `mazeVerifyText` variable set in onGenerationDone; in startSearch set verifyEl.innerHTML = mazeVerifyText. That way the "perfect maze" claim stays but the path claim disappears until re-verified. 

Then finish the replay and test A*.

Let me edit.

Now reload and test A*: set the select to A* and check. To change a select with the browser tool, I can click it and then click the option, or use `type`. Let me click the select at (553,128) then click the option. Native select dropdowns may not render in screenshots reliably. Alternative: focus the select and press Down arrow key.

Plan: reload → wait for solve (motion) → click select → key "ArrowDown" → this changes to A* and triggers replaySolver → screenshot mid-search.

Let me do reload + motion first.

Now let me pause mid-generation to inspect carving closely (the required "inspect maze-carving progress"), then switch to A*.

Actually let me use the Pause button to freeze the generation and inspect. Click Pause at (325,128) — but Pause is disabled during generation (btnPause.disabled=true until replay). Hmm, in newMaze I set btnPause.disabled = true, and it's only enabled in replaySolver. That's a UX flaw: you can't pause generation. Let me enable Pause during generation too (it's useful for inspection). Fix: in newMaze, set btnPause.disabled = false.

Also, when paused during generation, the loop still runs (raf continues, tick returns early after `if (paused) return;`) — fine, but render isn't called while paused so the frozen frame stays. Good.

Let me make that change, then reload, pause mid-generation, inspect, then A*.

Also note: `finishRun` disables pause; replaySolver enables. OK.

Edit: in newMaze, `btnPause.textContent='Pause'; btnPause.disabled=false;`.

Careful: if paused and then New Maze is clicked, paused is reset to false. Good.

Wait, there's a bug: if paused, tick() returns early and never renders, so the "Pause" freeze works. But if the user pauses and the loop is running, `raf` stays scheduled — fine.

However: `if (mode === 'done') stopLoop();` is after the `if (paused) return;` — if paused while mode==='done'... can't happen since done stops the loop.

Another subtlety: pausing during generation → tick returns early → no render → frozen frame. Resume → continues. ✓

Reload and test: pause mid-generation, inspect, resume, then A*.

Now Pause is enabled during generation. Let me click Pause to freeze and inspect carving closely.

The run completed before my Pause click landed (the tool click happened after generation+solving finished, ~2.5s later). The final state: path verified 81 cells, and the combined verification line reads nicely.

Looking at this solved maze: the gold path clearly follows corridors (I can verify visually: the path runs along open passages, and walls are visible as white lines that the path never crosses). This looks correct and much clearer than before.

Note the explored cells are only near the top (BFS found the goal quickly, 101 cells). Frontier cyan cells near the bottom-right. Good.

Now let me test A*. Click the select and press ArrowDown. Since focus matters, click on the select first, then key ArrowDown.

Note: the select change triggers replaySolver on this same maze.

The dropdown is open. Click the A* option at (540, 187).

The select still shows "BFS (breadth-first)" — my click at (540,187) landed after the dropdown closed, or the click on the option didn't register (native select popups aren't part of the page, so coordinates may not work). The DOM readout confirms the select value is still BFS and the maze is still solved with the same path (nothing happened).

Let me instead focus the select and use keyboard: click the select (opens dropdown), then press Escape? Better: use the `key` action with ArrowDown after focusing. Clicking the select opened the dropdown; a subsequent key press should move the selection. Let me try: click select at (553,128) then key "ArrowDown".

Actually simpler and more robust: click the select to focus, then press "ArrowDown" — but with the popup open, ArrowDown changes the highlighted option and Enter/blur commits. In Chromium, keyboard on a focused select changes value immediately on ArrowDown.

Let me do: click select, then key ArrowDown, then screenshot.

Note: my earlier click at (553,128) opened the dropdown and the screenshot showed it open. Then clicking at (540,187) apparently dismissed it without selecting (the popup is an OS overlay; the synthetic mouse event at that coordinate may have gone to the page beneath, closing the popup). So keyboard is the way.

I'm at ~13 min of the 15-min budget? Let me be efficient: do the two calls (click, key) and one screenshot, then finish with a final syntax check and report. Actually I can combine: click then key in one block? They're dependent (must focus first) but both are sequential tool calls; the harness allows multiple independent calls in one block — these are dependent in ordering but the tool executes them in order within a block? Risky. I'll do click+key as two calls but skip extra screenshots: after the key press, the returned DOM readout tells me the phase/value.

The dropdown is open again with BFS highlighted. Now press ArrowDown to select A*.

The select now shows "A* (Manhattan heuristic)" selected in the popup, but the phase is still SOLVED with the same stats — meaning the `change` event may not have fired yet while the popup is open (Chromium fires `change` when the popup closes / value committed). Let me press Enter/Escape to close the popup and commit, which should fire `change` → replaySolver with A*.

I'm running low on budget (~14 min). Let me press Escape (commits in Chromium) and check the DOM readout.

Let me use "Enter" as the key name.

Actually the tool takes `text` param for key action? Earlier I passed text: "ArrowDown" and it worked. Let me pass "Enter".

A* is now running on the same maze (walls unchanged — same maze as the BFS screenshot), the stale path claim is gone, and the exploration visibly follows open corridors (the blue wave hugs passages, frontier cyan at the leading edge). 

I'm at the end of my budget. Let me do a final quick sanity check that the file is valid (no syntax errors — the page is running fine, so JS parses) and confirm the file exists. Let me also verify the A* run completes with a verified path — one last screenshot after it finishes. That's cheap and valuable.

Let me do a quick `motion` or `screenshot` call to confirm the A* run finishes with path verification, then report.

Time's up. The A* run found the same 81-cell path on the same maze as BFS (proving walls unchanged and both solvers correct on the unique path). File is already saved. Let me do a final quick validation that the file is complete and well-formed, then report.

Everything is in place: single self-contained index.html, no external refs, JS syntax valid. Report concisely.