Matrix digital rain · step-5-preview

No chromium available directly. Let me check the browser tool availability. The browser tool exists in the function list. Let me write the index.html first.

Let me design the canvas digital rain.

Key implementation:
- Full screen black canvas, devicePixelRatio aware.
- Column objects with x position, y (in pixels), speed, glyph array, trail length, head char.
- Each frame: draw a semi-transparent black rect over canvas for fade trails, then draw glyphs.
- Actually to allow "Pause freezes animation", and "Restart resets columns and clears previous trails".

Approach: use offscreen rendering: keep a per-column list of glyphs with y positions in "grid steps". Each frame:
1. ctx.fillStyle = 'rgba(0,0,0,0.08)'; fillRect whole canvas — but this fades everything, causing trails to persist forever which is fine visually, but "no accumulating off-screen state" — that's about columns, fine. However, using the fade approach alone can leave faint residue. A cleaner approach: draw each column's glyphs explicitly with alpha based on index (dimmer further from head). That gives crisp fading trails and full control, and clearing on restart is easy.

Let me do explicit drawing: each column holds an array of glyph chars of length `len`, and `y` = head position in pixels. Each glyph drawn at y - i*fontSize, alpha decreasing with i, color varying brightness. Plus a bright white-ish head.

But note: the requirement says "brighter leading character and a fading trail" — explicit draw works.

For the "resize" test: "Resize the canvas and column layout to fit the viewport without stretching an old screenshot or leaving an uncovered strip." So on resize we must recompute fontSize and column count, rebuild columns, and not just scale the old canvas. Use ctx.setTransform to reset DPR transform and clear.

Implementation details:

```js
const glyphs = 'ｱｲｳｴｵｶｷｸｹｺｻｼｽｾｿﾀﾁﾂﾃﾄﾅﾆﾇﾈﾉﾊﾋﾌﾍﾎﾏﾐﾑﾒﾓﾔﾕﾖﾗﾘﾙﾚﾛﾜﾝ0123456789'.split('');
```

Font: measure fallback. Use a font stack: `'MS Gothic', 'Noto Sans Mono CJK JP', monospace`. Should be fine.

Font size based on viewport: fontSize = clamp(14, round(w/60), 22)? Standard: 16px, columns at fontSize*0.6? Actually typical column width = fontSize. Let's do columns spaced by fontSize.

Column state:
- x = col * fontSize
- speed: pixels per second, e.g. 60..200, scaled by fontSize
- headY: start negative random offset (above screen) 
- trailLen: number of glyphs, random 8..30
- glyphs: array of chars, updated randomly for flicker
- Also individual "advance": headY += speed*dt.

To add variety, per-column also a `brightness` and random "flicker" chance to change a glyph each frame.

Draw: for each column, for i in 0..trailLen-1: y = headY - i*fontSize; if within canvas, alpha = (1 - i/trailLen)^1.6 maybe; i=0 alpha 1 and color near white-green (brighter leading char), else green shades.

Also when column fully exits bottom (headY - trailLen*fontSize > height), recycle: headY = -random(0, 60)*fontSize, new speed, new trail length, new glyphs.

Also when reforming after resize, reset all.

High score/HUD: buttons Pause/Resume, Restart. Also keyboard shortcuts (space, R). And an FPS/columns readout maybe. Keep minimal but nice.

Also "Pause freezes the animation" — pause must also freeze flicker. Use rAF loop with `last` timestamp, and when paused, skip update and skip drawing? If paused, we stop drawing entirely (so nothing changes), and when resuming, don't do a huge dt jump (clamp dt).

Restart: reset dt accumulators, regenerate columns, clear canvas fully.

Careful: pause then restart should work.

Also handle visibility change to reset timer.

Let me write the code carefully.

Drawing performance: with 60 columns * 25 glyphs = 1500 fillText per frame — fine.

Let's write it.

Edge: on DPR, we set canvas.width = w*dpr, and ctx.setTransform(dpr,0,0,dpr,0,0).

Let me also add a subtle glow via shadowBlur on head only — shadowBlur is expensive but only 60 per frame. Maybe skip or keep small. I'll add shadowBlur for head chars with color rgba.

Now write file.

For the HUD overlay styling: small monospace text, semi-transparent.

Let me write it.

Also add a "trail density" maybe not needed.

Font selection: `font = `${fontSize}px "MS Gothic", "Osaka-Mono", "Noto Sans Mono CJK JP", "Hiragino Kaku Gothic ProN", monospace``. Katakana halfwidth ｱ may render in most fonts. Add fallback to ASCII letters if not — fine.

Let me now produce the file.

Now run in the browser and inspect.

Note: GLYPHS string contains 'ｼ' duplicated and '¦' — fine.

Let me test with the browser tool.

The canvas is black — no rain visible. Hmm, why? Possibly the canvas is not rendering. Let me check the console for errors. It seems the screenshot was taken very early (+0ms). Let's wait and take another screenshot, and check console errors.

Actually "Frame 1, +0ms" - it took the screenshot immediately. Let me screenshot again after a delay.

The rain is rendering. Issue: fps Infinity. That's because on the first frame, dt could be 0? Actually lastTime=0 initially and now is a large timestamp, so dt is large (0.1 clamped). Hmm, Infinity means dt === 0 → now === lastTime. But lastTime=0 is set only if lastTime===0... Wait: in frame(), `if (lastTime === 0) lastTime = now;` — so first frame sets lastTime = now, dt = 0. So fpsAvg = 1/0 = Infinity. Then subsequent frames average. It shows Infinity because the average didn't yet recover in the display? Actually fpsAvg = Infinity*0.9 + (1/dt)*0.1 = Infinity. Once Infinity, it stays Infinity. Bug. Fix: if dt <= 0, skip fps update.

Also, glyphs are rendering vertically top-to-bottom but text written vertically? No — they're stacked, fine.

Observations:
1. The columns look OK. Trails are visible. Head glyphs are brighter.
2. Text appears horizontally — good.

Concerns: The glyph texture at the top-left of the HUD overlaps with canvas. Fine.

One issue: the glyph rendering seems to show trails going upward from head. Good.

Another issue: the fps Infinity fix.

Also, glyphs look dense/overlapping — it's fine.

Also "cols 56" — good.

Let me also check the vertical spacing: characters have gaps. Fine.

Potential issue: When paused, does the image freeze? Let's test pause. Also test restart.

Also, an important check: resize. Let's test resizing the window and verifying no uncovered strip / no stretching. I can use browser drag? There's a `drag` action. Maybe simpler: check canvas dimensions via inspect. Let me check DOM attributes.

Let me first fix the fps bug, then test interactions.

Also I should double check: with `alpha: false` context, `clearCanvas` uses fillRect black — fine.

Another improvement: the head glyph's shadowBlur makes a glow — good.

Let me also add: while paused, pressing restart redraws a static frame — good.

Fix fps.

Wait — my first edit was wrong. Let me look at the current state of the frame function.

The original code:
```
    if (lastTime === 0) lastTime = now;
    // Clamp dt so tab-switches / stalls never teleport the rain.
    var dt = (now - lastTime) / 1000;
    lastTime = now;
    if (dt > 0.1) dt = 0.1;

    fpsAvg = fpsAvg === 0 ? 1 / dt : fpsAvg * 0.9 + (1 / dt) * 0.1;

    update(dt);
    draw();
```

Edit 1: replace "    update(dt);" with "    fpsAvg = ...\n\n    update(dt);" — but "    update(dt);" appears... it's unique? `update(dt)` - yes only one occurrence at that indentation (4 spaces). So it inserted the fpsAvg line before update.

Edit 2: replaced the original fpsAvg block with the new guarded version... wait, but edit 2's oldText contains the original fpsAvg line. Both edits target the same region?? They don't overlap: edit 1 inserted a NEW fpsAvg line before update(dt), and edit 2 replaced the ORIGINAL fpsAvg line. So now there could be TWO fpsAvg lines.

Hmm, actually edit 2's oldText: 
```
    var dt = (now - lastTime) / 1000;
    lastTime = now;
    if (dt > 0.1) dt = 0.1;

    fpsAvg = fpsAvg === 0 ? 1 / dt : fpsAvg * 0.9 + (1 / dt) * 0.1;
```
newText:
```
    var dt = (now - lastTime) / 1000;
    lastTime = now;
    if (dt > 0.1) dt = 0.1;

    if (dt > 0) {
      fpsAvg = fpsAvg === 0 ? 1 / dt : fpsAvg * 0.9 + (1 / dt) * 0.1;
    }
```

So that edit was a no-op basically in terms of what I wanted (I intended edit 2 to be the whole fix). And edit 1 added a duplicate. Let me read the file to check.

As suspected, there's a duplicate at line 328. Let me read lines 315-340 and fix properly.

Now fps 60, good. The rain is dense. 

Now let's test pause: click Pause button and verify image freezes. I need a way to compare. The screenshot tool returns an image; I can visually compare two screenshots after pausing. Let's click pause, screenshot, wait, screenshot again and compare the two images for pixel equality via bash? I can't easily save images from browser tool... Actually the screenshots are attached as images to me. I can visually compare.

Better: use JS evaluation to programmatically check. The browser tool doesn't have an eval action. But I can add a test hook? Not great to add test-only code, but I could use `inspect` to get DOM only.

Alternative approach: I can verify freeze by comparing two sequential screenshots visually (as the assistant I see the images). Let's do that.

Let me click Pause. First find button coordinates. The Pause button is at approximately x=68, y=25 in a 1200x800 viewport image? The image appears 1200x800. HUD is at top 14px + font 13px line-height ~ default 15px → button vertically centered around y≈25-30. Let's click (75, 25).

The click didn't pause it (state still running). The click at (75,25) probably missed the button. Let's inspect DOM to find the button bounding box. The `inspect` action might give element info. Let me try inspecting.

I notice a problem: the rain columns appear to only render on the LEFT portion of the screen? Looking at the screenshots, the right half of the screen (roughly x > 620) appears black/empty! Wait, the columns appear to be more dense on the left... Actually no — the image shows glyphs mostly in the left ~60% and the right 40% is empty black. Hmm, but earlier the "cols 56" with 1200px width at fontSize ~ 21 → 1200/21 = 57 columns. So columns should span the full width.

Wait, look closer: the right side is black. That's suspicious. Let me think about why.

Hmm! Maybe the canvas CSS width is 100vw but the actual canvas attribute width... no, both use `width`.

Oh wait — could it be that the glyph rendering happens but the screenshot is only showing partially? Let me look at the first screenshot after reload: glyphs covered left ~65%. And the far right was empty. Actually in the very first screenshot (frame 1, right after load, 2s later), the glyphs covered more area but still the right portion was empty.

Hmm, but wait: each column's glyphs drawn only when `y >= -fontSize && y <= height + fontSize`. At startup, head = rand(-height*0.9, -fontSize), so heads start above the screen and trails are above too — so initially NOTHING is visible. Then heads descend. After a few seconds, all columns should be visible across the full width.

Unless... the x positions: `i * pitch` where pitch = fontSize. columns.length = ceil(width/pitch)+1. So x from 0 to width. That covers full width.

So why is the right side empty? Let me reconsider: maybe the screenshot images are being cropped/scaled and I'm misjudging. The image looks like it's 1200x800 but maybe it's actually wider, and the visible glyphs region... Hmm.

Actually, look at the screenshots: there's a clear vertical boundary around 62% width where glyphs stop. That's odd.

Hmm, wait. Maybe the right side columns ARE there but with very low alpha because... no.

Let me reconsider: The stats div is at right bottom and visible at bottom right. The HUD at top-left.

Another thought: the `draw()` function: `ctx.textAlign='center'`. So glyph centered at col.x. Fine.

Could `ctx.font = fontSize + 'px ' + FONT_STACK;` fail? No.

Let me test more concretely: use browser `inspect` — it only gives dom text. Hmm, no pixel data.

Better idea: I can add a temporary debug — write a small standalone test harness. Actually, I could take a screenshot with the browser tool and analyze the image... I can't save the image to disk though. But maybe I can! The browser tool output attaches images; I can't download them.

Alternative: Use node with a canvas implementation? No canvas module available.

Hmm, let me think about why the right side is empty. 

OH WAIT. I see it. The screenshot might be from a viewport where the browser window is wider than 1200 and the screenshot is a crop? The tool says coordinates use 1200x800 viewport. The attached image is likely 1200x800.

Let me count columns visually. Hmm.

Actually, let me reconsider — maybe the issue is that many columns recycle: `if (col.head - col.len*fontSize > height) recycle(col)`. After recycle, head = rand(-height*0.75, -fontSize). So heads are above screen, trails above. Fine, they come down.

But note that `col.glyphs` array when len changes is rebuilt. OK.

Hmm, is it possible that the draw loop `for (var g = len - 1; g >= 1; g--)` skips... no.

Let me just check: maybe the right part of the screen is covered by something? The `#stats` is at bottom right with pointer-events none.

Actually!!! I bet the issue is this: the screenshot images are 1200 wide but the actual page viewport in the headless browser might be narrower (e.g., ~780px), and the canvas is 100vw so it covers only the left part, while the rest of the screenshot is... no, the rest would be white/black body background (body is black). So if the viewport were e.g. 800px wide, we'd see rain in the left 800px and black beyond. That matches the boundary at ~62%!

So the actual viewport width is ~750-800px, and the screenshot is 1200 wide with the rest black. That would explain it. Let's verify by checking the stats "cols 56": 56 columns at pitch fontSize. If width were 1200 and fontSize = round(min(1200/55, 800/34)) = round(min(21.8, 23.5)) = 22 → ceil(1200/22)+1 = 56. Hmm, that gives 56 for width=1200. If width were 750: fontSize = round(min(13.6, 23.5)) = 14 → ceil(750/14)+1 = 55. Also ~55-56. Ambiguous.

Better test: resize behavior check + measuring via a different approach. I can determine the real viewport by checking how many pixels wide the rain region is: from the screenshots, the boundary is around x≈750/1200 → 62.5% → 750px. Hmm, if viewport is 750 wide, then fontSize=14, and 55 columns.

Actually the tool docs say "Coordinates use a 1200×800 viewport", which suggests the browser viewport is 1200x800. But the observed boundary contradicts.

Let me test definitively: I'll add a temporary debug line that writes the canvas dimensions into the DOM (e.g., the stats text), reload, and read the DOM via inspect. That's actually useful info to display anyway. Let me add "size WxH · dpr" to the stats area permanently — it's reasonable for a debug HUD, and helps verify resize.

Let me add that.

So the viewport IS 1200x800, css 1200x800, dpr 1, cell 22, 56 columns. So the right side should have columns!

So why does the right part of the screen appear empty in the screenshots? Let me reconsider... Maybe the screenshot is rendered at a lower resolution and downscaled, and I'm misreading. Let's look again at the last screenshot: glyphs appear at the top around x≈1000 (ｱ, ｷ visible). Hmm, in the screenshot just now, there are glyphs at top around x=990 and x=1060 ("ｱ" "ｷ"). So the right side DOES have some glyphs — they're just sparse/scarce.

Wait, why would the right side be much emptier than the left? All columns are identical in distribution... 

OH. I think I understand! The screenshots are taken at various moments, and the columns' trails are only visible when the head is on-screen. But ALL columns should eventually be on screen. Unless... most columns have `head - len*fontSize > height` triggers recycle and they restart from above.

Hmm, but here's the thing: columns are recycled only after their whole trail is below the screen. So at any moment roughly the same fraction is visible across x.

Unless the number of glyphs drawn per column depends on... hmm.

Wait, actually let me reconsider the visual. In the screenshot at 2s after reload, in the left region there were long dense trails; the right region had a few. Look at the screenshot from "sleep 2 then screenshot" earlier: I see glyphs in the left 2/3 with density, and the right third (x>~780) mostly empty but with a few sparse glyphs. And there were visible glyphs at x≈1150 in one shot (the "ｱ" "ｷ" at top).

Hypothesis: the columns' alpha. The `hsla` color with alpha near zero for the tail. But that's the same for all columns.

Alternative hypothesis: the screenshot images are compressed/scaled (the browser screenshot may be downscaled to a fixed width, e.g., 1200 wide but source larger). If the actual viewport is 1200x800 then no scaling.

Hmm, but wait: maybe the browser window viewport is actually much larger, like 2400x1600, and the canvas is 100vw = 2400 wide, but the DOM reported css 1200x800? No, the DOM readout uses window.innerWidth which would report the real viewport. So the viewport is 1200x800.

So the canvas covers 1200x800, matching the screenshot. Then why is the right region empty?

Let me count more carefully. Let me look at the 2-second screenshot again (the second one). Right region: at top I see "ﾅ" "ｷ" around x≈1000-1060 near y≈30. At the right edge around x≈1160, y≈300-400, there are some glyphs "ﾆ" "ﾅ"... Actually in that screenshot, at the far right I see vertical columns of glyphs at x≈1120-1170 (e.g., "ｾﾆﾅｶ"?). Hmm, I recall seeing "ﾆｼﾞﾑﾛ" etc.

Honestly, the density difference may just be a coincidence of timing: the rain trails are ~8-30 glyphs * 22px = 176-660px tall, so a column covers at most ~80% of the 800px height. With 56 columns and heads spread randomly, at any instant maybe 60-70% of columns have their head on-screen. But that would be uniform across x.

Unless... AH WAIT. I think I've got it! `Math.random()` at boot: `col.head = rand(-height * 0.9, -fontSize)` — that's fine and independent per column.

Hmm, what if it's the browser screenshot being partially rendered (the canvas compositing)? Let me try taking a screenshot at a later time, like 6 seconds, to see if the right fills in.

Actually, let me reconsider the possibility that the screenshots ARE showing the full canvas but the glyphs on the right are just... hmm.

Let me do a controlled experiment: take two screenshots ~1.5s apart and diff them mentally. If the right side never changes, it's suspicious.

Actually, a much better approach: temporarily add a debug draw that fills a colored rect at a specific x to check pixel mapping. Too convoluted.

Alternative: Let me use the browser `motion` action which captures motion frames — that might reveal which regions change over time. Motion detection would show the moving areas! That's a great way to see the full rain coverage.

Let me first take a screenshot after more time, then try motion.

Actually hold on. Let me re-examine: maybe the issue is the `hsla` alpha computation for the trail. `alpha = pow(1-t,1.7)*0.85*bright`. For the head t=0 → alpha 0.85*bright. That's fine, visible.

Hmm, but what about `ctx.fillStyle = 'hsla(...)'` with `alpha.toFixed(3)` — fine.

Wait... maybe the issue: many columns recycle repeatedly because `recycle` sets head to `rand(-height*0.75, -fontSize)` = between -600 and -22. Fine.

OK here's another thought: What if the browser screenshot is a scaled-down capture of a larger viewport? The tool says the viewport is 1200x800 for coordinates. The canvas readout came from JS innerWidth = 1200. So consistent.

I'll just check with the `motion` tool, which likely shows frames where pixels changed. If the right half shows motion, then the rain covers it.

Actually, simplest: take a screenshot now (several seconds in) and look carefully at the right half.

I'm considering whether to use the motion action to capture frames and display them as images, which might reveal changes between frames in the browser environment.

Now I can see the rain covers the full width, including the right side (e.g., x≈1100-1180 has glyphs in frame 4). The columns are independently moving — comparing frames, heads advance and different columns appear/disappear. Good.

Note that glyph brightness: heads are bright (e.g., "ﾎ", "ﾃ" brighter), trails fade. Good.

Now, one issue I notice: the glyphs seem to overlap horizontally somewhat? Looks fine.

Another observation: many columns appear to have a slight "smear"? Fine.

Now let's test Pause. I need to click the Pause button correctly. Earlier my click at (75,25) didn't register. The button "Pause" — from the DOM, HUD at top 14, left 14. The title "MATRIX RAIN" text, then buttons. The button's bounding box: let's estimate. Actually the click may have failed because the click coordinates were relative to the iframe viewport which might be offset. The image is 1200x800 and HUD appears at x≈14..120, y≈14..40. "Pause" button center maybe (75, 27).

Earlier click at (75,25) returned "Frame 1" and the animation kept running. Hmm, maybe the click did work but the screenshot shown was taken before? No, state stayed "running".

Maybe the issue is that the browser tool needs a small delay before screenshotting. Let me try clicking again and then check the DOM text separately (click action returns dom info).

Let's click at (80, 30).

The click isn't registering on the button. fps still 60, state running.

Maybe the click coordinates are being mapped differently — perhaps the browser tool clicks at coordinates relative to a screenshot that's scaled, or maybe there's an offset for the HUD coordinates.

Let me try clicking exactly in the middle of the "Pause" text. In the screenshot, "Pause" appears around x=68..100, y=22..36. Center ≈ (84, 29). I clicked (80,30). Hmm.

Maybe the issue is that the clicks work but the state readout is stale (from before the click)? The dom reported "state running" but the screenshot shows... the button label "Pause" — if paused, the label would be "Resume". The screenshot shows "Pause", so it's running.

Wait — maybe the pause happened and then the click toggled twice? No.

Possibility: the browser tool's click dispatches at coordinates but the canvas has `position: fixed` and covers the viewport, and the HUD is above with z-index 10 — should receive clicks.

Hmm, unless the click event target is the button but... the `keydown` listener? No.

Let me check whether the harness's click works at all: maybe it requires the element to be found. Let me try `type` or keyboard instead: press Space to toggle pause. The key action might send a key to the page. Let's try pressing Space and check whether state becomes paused.

Actually, before that — maybe the problem is the click lands on the button, the handler runs `toggle()`, but `running` was false... no, it's true.

Hmm wait, actually! Look at my `start()` function:

```
function start() {
    if (running) return;
    running = true;
    ...
    rafId = window.requestAnimationFrame(frame);
}
```

and `toggle() { running ? pause() : start(); }`. That's fine.

But note: `document.addEventListener('visibilitychange', ...)` sets lastTime = 0 — harmless.

Let me test with the keyboard: press "p".

Pause works via keyboard: state paused, fps 0, button label "Resume". The image is frozen (the canvas retains its last frame).

Now let's verify the freeze by taking two screenshots separated in time and confirming they're identical. Let me take a screenshot now, wait, and take another.

Then test resume with Space, then restart with R, verifying trails are cleared.

Note the buttons didn't respond to click. Let me investigate: perhaps the browser click coordinates need to target the canvas coordinate space; the click at (80,30) might be inside the button bounding box... Let me check the button position more carefully by measuring in the rendered image: "Pause" button spans roughly x=66..102, y=21..38. Center (84, 29.5). I clicked (80,30) — should hit.

Hmm, maybe the harness's click sends a mouse event to a specific element via coordinates but computed with device pixel ratio scaling where the iframe is smaller? Since the canvas is 1200x800 CSS = viewport, and dpr=1, no scaling.

Wait, maybe the click IS working but toggles twice quickly? No.

Or maybe the tool's click uses `page.mouse.click(x, y)` in the browser but the page has `pointer-events` issues... The `#hud` has z-index 10 and is position fixed — should be on top.

Hmm, but here's a thought: the canvas is `position: fixed; top:0; left:0; width:100vw; height:100vh;` with `display:block`. The HUD is a sibling with position fixed and z-index 10. Since HUD comes after canvas in DOM order and has z-index 10, it's on top. Clicking at (80,30) should hit the button.

Unless... the iframe viewport for the harness is 1200x800 but the actual rendered page inside the iframe is scaled (e.g., the screenshot is a scaled-up image of a smaller viewport). But the canvas readout says css 1200x800 based on window.innerWidth. So the viewport is 1200x800 for real.

So why doesn't the click work? Possibly the harness's click is being delivered to the iframe's document at coordinates that don't account for the iframe's offset within the screenshot. Maybe the screenshot includes the iframe at an offset (e.g., the iframe doesn't start at 0,0). The screenshots appear to show the HUD at the top-left corner, so the offset is likely 0.

Hmm, alternatively, the click may need the target element to be visible at those coordinates — perhaps there's something overlaying that intercepts at (80,30)? The `#stats` is bottom-right, pointer-events none. 

Let me try clicking at the exact center of the Restart button (~(160, 29)) and see if anything happens. If that doesn't work either, the click mechanism might be broken in this harness, and keyboard shortcuts suffice for verification. But since the task requires the buttons to work, I should verify they actually work. I can also make the buttons more robust (they're plain buttons with click listeners).

Actually — WAIT. I bet I know the issue! The keyboard `keydown` listener with `e.code === 'Space'`... no, that's keyboard.

Hmm, what about `#hud` having `user-select: none` — irrelevant.

Let me look at the DOM more carefully. Maybe the harness's click works but the coordinates are in a scaled space: the screenshot images might be rendered at 1200x800 but the actual page viewport might be 1200x800 — consistent.

Let me try a click at (200, 100) — in the middle of black canvas area — and see if the frame changes... that wouldn't show anything visible.

Better test: click on "Restart" at around (165, 29): if restart works, the trails clear and the screen becomes mostly black (columns start above the screen). That's an easily observable effect! Let's try.

The image is identical to the paused frame from 3+ seconds earlier — the animation is frozen. 

Now test resume: press Space again and verify it continues (image changes).

Resumed: fps 60, state running, and the image changed (columns advanced).

Now test Restart via the button click (which earlier didn't seem to work) — this time the goal is also to verify that clicking the button works. Let me click Restart at approximately (168, 29).

Actually wait, earlier the click on Pause at (80,30) didn't work. Let me reconsider why. Maybe the harness dispatches a click at those coords but the element is a `<button>` inside `#hud` which is `position: fixed` — clicks should work.

Hmm... maybe the harness click coordinates are for the top-level page, and the app runs inside an iframe whose visible area is offset. The screenshots might be of the iframe only (1200x800). If the iframe occupies the full browser window, coordinates match.

Let me try a different approach to figure out the click mapping: click at (168,29) for Restart. If trails clear → click worked. If nothing happens → try other coordinates.

Actually, let me first try the keyboard R to verify restart clears trails, then try the button click to check whether clicking works at all.

Restart works: the screen is now black (all trails cleared, columns start above the viewport). 

Now let's test the Restart button click, and also resize behavior. For resize, I can use the `drag` action on the window? Probably not. Alternatively I can test the resize handler by simulating via the browser viewport... The harness has a fixed 1200x800 viewport.

Hmm, how to test resize? Options:
1. Use `drag` to resize the window — not applicable (it'd drag on the page).
2. Trust the resize code (tested by review) — but the requirement is important.

I could verify resize logic in a headless way: extract the JS logic into a node test with a fake DOM? That's heavy but doable: I could simulate by evaluating the script in a jsdom-like environment. No jsdom available.

Alternative: Use the browser tool's `inspect`/`screenshot` after simulating a resize event via keyboard? Not possible without eval.

Hmm — but maybe I can verify resize differently: I can dispatch a resize by changing the viewport through the browser tool? Not available.

Wait — maybe I can use the mobile emulation? No.

Option: I can add a temporary test hook in the page that calls resize() with fake dimensions, e.g., a hidden debug function exposed on window and a small on-screen "test size" button... but modifying the app for testing is undesirable; still, exposing a debug hook isn't harmful if unobtrusive. Actually, a simpler and legitimate approach: temporarily add a query-param-driven test that forces a viewport size, test, then remove. But that costs time.

Alternative approach: verify the resize logic by writing a small node harness that stubs `document`, `window`, and a fake canvas context that records calls. The script is an IIFE using document.getElementById, canvas.getContext, window.addEventListener, requestAnimationFrame. I can stub all of these in node with a minimal fake, including a recording 2D context. Then I can call the captured 'resize' handler with a fake window.innerWidth/innerHeight and assert:
- canvas.width/height updated to match
- ctx.setTransform called with (dpr,0,0,dpr,0,0)
- fillRect called with full backing size (clearing)
- columns rebuilt with count matching new width
- no drawing with stale transform

This is a solid verification approach that doesn't touch the app. Let's do it — it's fast.

Let me write the harness:

```js
const fs = require('fs');
const src = fs.readFileSync('index.html','utf8').match(/<script>([\s\S]*?)<\/script>/)[1];

function makeCtx() {
  const calls = [];
  const ctx = {
    calls,
    setTransform(...a){calls.push(['setTransform',...a]);},
    fillRect(...a){calls.push(['fillRect',...a]);},
    fillText(...a){calls.push(['fillText',...a]);},
    save(){}, restore(){},
    set fillStyle(v){calls.push(['fillStyle',v]);}, get fillStyle(){return '';},
    set font(v){calls.push(['font',v]);}, get font(){return '';},
    set textAlign(v){}, set textBaseline(v){},
    set shadowColor(v){}, set shadowBlur(v){}
  };
  return ctx;
}
```
Careful: `ctx.fillStyle = ...` assignment in a plain object works normally (no getter/setter needed). Using setters that record is fine but then reading isn't needed. Simpler: just use plain properties, and record fillRect/setTransform/fillText.

I need `document.getElementById` to return elements with addEventListener, textContent, innerHTML. And `window` with addEventListener, requestAnimationFrame, cancelAnimationFrame, innerWidth, innerHeight, devicePixelRatio, clearTimeout, setTimeout.

Also `document.addEventListener` for visibilitychange.

The script also immediately calls resize(), draw(), start() at boot. With a fake rAF that doesn't call the callback, frame never runs. Good — I'll control the captured frame callback manually.

Let me capture the rAF callback so I can step frames.

Then test:
1. Boot at 1200x800 dpr 1 → canvas.width=1200, height=800, setTransform(1,0,0,1,0,0), columns count = ceil(1200/22)+1 = 56. Verify by checking the internal state? I can't access internals of the IIFE. But I can check the stat readouts via the fake element textContent: statCols.textContent should be '56'. And statSize.innerHTML contains canvas dims.

2. Fire the captured 'resize' window handler after changing innerWidth to 900, innerHeight 500, devicePixelRatio 2 → expect canvas.width=1800, height=1000, setTransform(2,...), statCols = ceil(900/fontSize)+1 where fontSize = round(max(12,min(26,min(900/55,500/34)))) = round(min(16.36,14.7)) = 15 → ceil(900/15)+1 = 61. And a fillRect covering the whole backing store (clear) — check that a fillRect(0,0,1800,1000) call occurs after the size change (in device pixels).

Wait, `clearCanvas` uses setTransform(1,0,0,1,0,0) then fillRect(0,0,canvas.width,canvas.height) — good, full coverage.

3. Also verify draw() after resize uses new coordinates: run a frame and check fillText x values are within new CSS width (i.e., max x < 900) — confirms no uncovered strip and columns built for the new width.

Also verify recycling: run many frames with a large dt and confirm the number of columns stays constant (no accumulation) — check statCols text stays the same and that no new arrays are created... simplest: after running 500 frames of dt=0.1, statCols remains 61 and drawing continues to work (fillText calls succeed). Also I can check that heads stay within bounds by inspecting fillText y values — after many frames, all drawn y should be within [-fontSize, height+fontSize]... Actually when a column is recycled, its head goes above the screen so nothing is drawn for it until it re-enters. So drawn y values are always within the visible range. I can assert that across many frames: all fillText y in [-fontSize, height+fontSize]. That verifies "no accumulating off-screen state".

This is a good automated verification. Let me write it.

Note: the fake `ctx` needs `fillRect` etc. Also `canvas.style` object. And `canvas.getContext` returns the fake ctx.

Also the script uses `window.requestAnimationFrame` — I'll implement a queue.

Let me write the harness now.

The harness isn't exercising the app: cols stayed 56 and no glyphs drawn, and resize handler didn't update. The issue: `winLog.find(e => e[0] === 'resize')` — my fake `addEventListener` pushes [type, fn] for window. But the script calls `window.addEventListener(...)`. Since `global.window = win` and the script references `window` — inside `new Function(src)`, `window` resolves to the global property. That should work.

Hmm, but the issue could be that the script uses `window.innerWidth` (fine) — but the app seems to have booted with 1200x800 (default W/H). And resize did nothing... 

Ah, I see the problem: the resize handler is debounced with setTimeout(60), but my call `resizeHandler()()` calls the listener directly, so it should run resize(). Unless resizeHandler() returned undefined — meaning winLog has no 'resize' entry?? But then `resizeHandler()()` would throw TypeError. It didn't throw, so the handler exists and ran.

Wait, but if the handler ran, canvas.width should be 1800. Unless... `resize()` computed `needsRebuild` false and... no, it always sets canvas.width.

Unless the handler found is from a different source. Hmm.

OH WAIT. The real problem: `document.getElementById(id) { return els[id] || (els[id] = el(id)); }` — this creates elements lazily. The script ran `resize()`, `draw()`, `start()` at boot. But `start()` calls `requestAnimationFrame(frame)`. My `step()` runs queued callbacks. That should work.

But 0 glyphs drawn... The `draw()` at boot draws glyphs only if heads are on screen (they start above). So boot draw = 0 glyphs is expected. Then frames should draw.

But `step(1000/60)` → the queued callback is called with now=16.67. In frame(): `if (lastTime === 0) lastTime = now;` — but lastTime is set to 0 again when...? In `start()`, lastTime = 0. Then first frame: lastTime = 16.67, dt = 0. Then next frames: dt = 16.67-1000/60... wait, I pass the SAME ms value each time (1000/60)! So dt = 0 every frame → nothing moves → no glyphs ever drawn (heads never advance from off-screen). That's the harness bug.

I need to increment the timestamp: step(i * 16.67).

Also `fpsAvg` not relevant.

And the resize test: my `resizeHandler()()` call — hmm, canvas.width should have been set to 1800 regardless. Unless the exception... Let me check: after `resize()` at boot, `updateSizeReadout()` was called, setting statSize.innerHTML with canvas.width... but the "after resize" log shows 1200x800 unchanged. So resize didn't take effect.

Wait — maybe `resizeHandler()` returned a handler from an earlier registration... no.

Hmm, maybe the issue is that `new Function(src)()` — the script body starts with `(function () { 'use strict'; ... })();` so it's fine.

Let me debug: print winLog types and whether resize() ran. Possibly the `document.addEventListener('visibilitychange')` etc. Let me check: my document stub lacks... it has addEventListener. Fine.

Actually! I wonder whether `resize()` threw an exception inside the resize handler (e.g., `statSize` undefined?) — `updateSizeReadout` uses statSize which exists. Hmm.

But actually, wait: could the whole boot have thrown? If `resize()` threw at boot, then `draw()`/`start()` wouldn't run, and the IIFE would throw out of `new Function(src)()` — uncaught, so my script would have crashed. It didn't crash. So boot completed, including `draw()` and `start()`.

Let me actually debug by adding prints. Also the dt issue: with dt=0, update does nothing, draw draws nothing (heads off-screen). That explains 0 glyphs.

For the resize: OH! I see it now. In `resize()`, the local variable `needsRebuild` is computed... and canvas.width is set unconditionally. So it must be 1800 after the handler. Unless the handler I called isn't resize...

Hmm, `winLog.find(e => e[0] === 'resize')` — my fake addEventListener pushes `[type, fn]` where type is like 'resize', 'keydown', 'orientationchange'. Yes.

Unless... `resizeHandler()()` — I wrote `resizeHandler()()`. That's calling the result. Right.

Wait, maybe the exception occurred inside the handler and was swallowed by the fake setTimeout? No, the handler runs synchronously.

Hmm, actually — maybe `window.getComputedStyle`... no.

Let me just debug it directly.

Actually hold on! Look at the output more carefully: "after resize: cols=56 size=canvas 1200x800". Since resize sets W=900 globally, but `resize()` reads `window.innerWidth` — which is the getter on `win` → 900. So canvas.width = round(900*2)=1800.

Unless the handler that ran was... Let me add a print inside. Let me debug.

So the resize handler runs but canvas.width stays 1200x800! That means `resize()` read window.innerWidth as 1200 — i.e., the app captured something else... 

OH! I see it. In `resize()`:

```
var w = Math.max(1, window.innerWidth);
```

That reads the live getter → 900. Hmm.

Unless... `needsRebuild` false → but canvas.width assignment is unconditional...

WAIT. Look at the order in my edited file. Let me re-read resize():

```
function resize() {
    var w = Math.max(1, window.innerWidth);
    ...
    width = w; height = h; dpr = ratio; fontSize = newFont;
    canvas.width = Math.round(width * dpr);
    ...
```

Hmm, that should be 1800. Unless there's an early return or the function was overwritten...

OR: the assignment `canvas.width = ...` — my fake canvas object is a plain object with width property. Assignment works. Unless `canvas` variable inside the IIFE refers to `document.getElementById('rain')` — my stub returns `els['rain']` which I set BEFORE running (els.rain = {...}). Yes, that's the same object. And after boot canvas.width = 1200 confirms it's the same object. So assignment works.

So why didn't it change? Because `window.innerWidth` returned 1200?? My getter... `get innerWidth(){return W;}` and I set W=900 before calling. Unless the handler captured something...

Hmm wait, is it possible the resize listener is NOT the debounced function but... it is: `window.addEventListener('resize', function () {...})`. Calling it runs clearTimeout + setTimeout(resize, 60) — and my fake setTimeout returns 0 WITHOUT calling resize! THERE's the bug in my harness: the resize listener is debounced, so calling it doesn't invoke resize() directly.

In the earlier verify.js I had `setTimeout: (fn,t)=>setTimeout(fn,t)` — a real timer, so it would eventually fire but after the synchronous script ends... Actually `setTimeout(resize, 60)` real → fires after the script ends; but the script's synchronous part finished before, so the checks ran too early. Also `clearTimeout(resizeTimer)` with a real id... Since the harness ended synchronously, callbacks never ran. That explains all the resize failures.

Fix: make the harness's setTimeout execute the callback immediately (or capture it). Best: implement a fake that stores the pending callback and let me flush it manually.

Let me update verify.js: `setTimeout(fn){ pending.push(fn); return pending.length; }` and `flushTimers(){ pending.splice(0).forEach(f=>f()); }`. And clearTimeout → remove? Keep simple: track ids.

Also fix dt: step with increasing timestamps.

Let me rewrite verify.js accordingly.

Good progress. Remaining "failures" are harness artifacts:

1. "boot uses dpr transform" — my check looks for setTransform with c[1]===1 && c[4]===0. In boot, `clearCanvas` does setTransform(1,0,0,1,0,0) → args [1,0,0,1,0,0], c[1]=1, c[4]=0 → should pass. But the log array is shared... wait, the log is `makeCtx([])` — a fresh array. But at boot, the log entries: setTransform(1,0,0,1,0,0) from clearCanvas at the end of resize. Also draw() calls save/restore — no setTransform. So the check should pass. Unless the order: resize() → clearCanvas() → setTransform(1,...) — yes logged. Hmm, why fail?

Oh! Because my check ran AFTER the 20 frames of `advance()`, and `ctx.log` — no, log accumulates, never cleared. So `ctx.log.some(...)` should find it.

Wait... unless `setTransform` gets called with (1,0,0,1,0,0) — c[1] is 1 → true, c[4] is 0 → true. Should be true. Let me print the log to check. Maybe the Proxy... no, in verify.js the ctx is a real object with methods. Let me check `makeCtx`:

```js
function makeCtx(log) {
  return {
    log,
    fillStyle: '', font: '', ...
    setTransform() { log.push(['setTransform', ...[].slice.call(arguments)]); },
```
That's fine.

Hmm, but hold on: does the app call `ctx.setTransform` or does it maybe fail because `ctx.save()`/`restore()`... no.

Actually! I bet the issue is: `resize()` is called at boot BEFORE `clearCanvas()`... and the log's first entry... let me just debug print.

2. "draws glyphs -> 254 glyphs" with my threshold of 500 — the count is over 20 frames but heads start above the screen so few visible. That's fine; threshold too strict. Let me lower to >100. Actually 254 for 20 frames ≈ 12.7 glyphs/frame. Hmm, that seems low: after 20 frames (0.33s), columns have moved 0.33 * speed(~90-330) ≈ 30-110px. Heads start at rand(-height*0.9, -fontSize) → e.g., -720..-22 at 1200x800... wait, `rand(-height*0.9, -fontSize)` = rand(-720, -22). So heads are between -720 and -22 — mostly far above. After 0.33s, most are still off-screen. So 12 glyphs/frame visible is plausible. Fine — lower threshold.

3. "post-resize framebuffer never rescaled/stale" FAIL: my check asserts no setTransform with c[1] !== 2. But `clearCanvas()` (called by resize) does setTransform(1,0,0,1,0,0) — that's the intentional clear, not a stale scale. My assertion is too strict. It should allow the reset-to-identity clear. Let me refine: assert that the LAST setTransform after the size change is (2,...) i.e., the drawing transform. Actually the sequence in resize: setTransform(dpr) then clearCanvas → setTransform(1) then restore() → back to (2). Wait: `ctx.save(); ctx.setTransform(1,...); fillRect; ctx.restore();` — save/restore restores the (dpr) transform. Then buildColumns, updateSizeReadout. So after resize, the current transform is (dpr,0,0,dpr,0,0). Good. The draw() in subsequent frames doesn't setTransform.

So my check should be: the last setTransform call in the log is (2,0,0,2,0,0). Let me fix.

For #1, let me debug what's in the log.

Also y range at boot: [-21.7, 90.1] — heads entering. Fine.

Let me debug the log content.

The boot does call setTransform(1,0,0,1,0,0). So why did the check fail in verify.js? Because in verify.js, `makeCtx([])` passes a log array, but the check looks for `c[0]==='setTransform' && c[1]===1 && c[4]===0`. c = ['setTransform',1,0,0,1,0,0] → c[1]=1, c[4]=0. Should be TRUE...

Hmm wait, in verify.js the check is:
```js
report('boot uses dpr transform (no stale stretch)',
  ctx.log.some(c => c[0] === 'setTransform' && c[1] === 1 && c[4] === 0));
```
That should pass. Unless... `makeCtx` in verify.js is defined as:

```js
function makeCtx(log) {
  return {
    log,
    ...
```
Hmm, and the canvas `getContext() { return ctx; }` where `const ctx = makeCtx([]);`. So ctx.log is the same array referenced. So ctx.log has entries. 

OH WAIT. The `report` for that check ran BEFORE... no.

Hmm, hold on: maybe the issue is `els.rain = canvas;` — but in verify.js, `el(id)` has `click(){}`... and `document.getElementById` returns `els[id] || (els[id] = el(id))`. Since I set els.rain = canvas before running, getElementById('rain') returns my canvas. Fine.

So why did it fail? Let me re-run verify.js with a debug print of ctx.log's setTransform entries. Maybe the `[...].slice.call(arguments)` inside makeCtx... that's in verify.js:

```js
setTransform() { log.push(['setTransform', ...[].slice.call(arguments)]); },
```
Hmm — `...[].slice.call(arguments)` — spread of an array. That works. But wait: `...[].slice.call(arguments)` — is `[].slice.call(arguments)` = arguments array? Yes.

Hmm, but in a non-strict function, arguments→array conversion is fine.

Let me just print in verify.js. Actually — I wonder if the problem is that the 'boot uses dpr transform' report ran when `ctx.log` was... Let me add a print of ctx.log.filter(setTransform) length right before that report.

Actually!!! I know! In verify.js, `makeCtx` is defined with parameter `log`, and the returned object has a property named `log`. But the object ALSO has methods `setTransform() { log.push(...) }` which reference the outer `log` parameter — fine.

Hmm, so let me just debug-print. Let me add a temporary print.

The log has setTransform entries that should satisfy the condition... `c[1]===1 && c[4]===0` — for `['setTransform',1,0,0,1,0,0]`, c[1] is 1 ✓, c[4] is 0 ✓. So `some` should be true!

Unless... the `report` call evaluates the condition but `ctx.log` — WAIT. Look at report signature: `function report(label, cond, extra)`. And the call:

```js
report('boot uses dpr transform (no stale stretch)',
  ctx.log.some(c => c[0] === 'setTransform' && c[1] === 1 && c[4] === 0));
```

Hmm that's fine... unless the string in the file differs. Let me look at the actual line in verify.js. Maybe there's an arrow-function issue with `=>` and... no.

OH WAIT!! I see it. In verify.js the canvas creation:

```js
const ctx = makeCtx([]);
```

and `makeCtx(log)` returns `{ log, ... }`. So `ctx.log` is the same array. Fine...

Hmm, but the DBG output shows ctx.log has 4 entries — so `ctx.log` works and has the setTransform entries. So `.some(...)` must be true. Unless the condition in the actual file is different from what I think. Let me grep the exact line.

The condition looks right. Wait — `resize sets dpr transform` PASSED with `c[1] === 2`, meaning `.some` works. And the boot one with `c[1]===1 && c[4]===0` FAILED while the DBG print shows `["setTransform",1,0,0,1,0,0]`.

Hmm! `...[].slice.call(arguments)` — spread in an array literal. `[].slice.call(arguments)` gives [1,0,0,1,0,0]. So the entry is ['setTransform',1,0,0,1,0,0] — 6 elements. c[4] = 0.

Wait, wait. Maybe the `['setTransform', ...]` spread in a method shorthand in a non-strict... no.

Hmm, DBG printed total log 4 but earlier run showed draws 254 glyphs across 20 frames... that's a separate phase. At the time of the boot check, log length is 4 — matches the DBG output.

So `ctx.log.some(c => c[0] === 'setTransform' && c[1] === 1 && c[4] === 0)` on `[["setTransform",1,0,0,1,0,0],["setTransform",1,0,0,1,0,0],["fillRect",0,0,1200,800],["fillRect",0,0,1200,800]]` ... 

For the fillRect entries: c[0]='fillRect' → false, short-circuits. For setTransform entries: c[0]==='setTransform' true, c[1]===1 true, c[4]===0 true → TRUE.

This is bizarre. Unless... the file being run by node is not the same as what I grepped? I ran `node verify.dbg.js` for the DBG output which is a copy. And the FAIL was from... wait, in the DBG output the report right after DBG printed FAIL. So the same file, same ctx.log... 

OH!!! I GOT IT. `report(label, cond, extra)` — the FAIL line prints `(cond ? 'PASS' : 'FAIL')`. But hold on, is it possible that the arrow function `c => ...` where `c` shadows something? No.

Hmm, is it possible that `c[4]` for `["setTransform",1,0,0,1,0,0]`... indices: 0='setTransform', 1=1, 2=0, 3=0, 4=1, 5=0. 

AH HA! THERE IT IS! `['setTransform', 1, 0, 0, 1, 0, 0]` — index 1 is the FIRST argument (a=1), index 2 is b=0, index 3 is c=0, index 4 is d=1, index 5 is e=0. So c[4] = 1, not 0! I mislabeled. The check should be `c[1]===1 && c[2]===0 && c[3]===0 && c[4]===1 && c[5]===0`.

That's my harness bug. The transform scale is at index 1 (a) and 4 (d). Let me fix the assertion to check the diagonal: c[1]===1 && c[4]===1.

Same for the resize check (c[1]===2 passed since a=2 ✓).

And the "post-resize framebuffer never rescaled/stale" check: I want to assert that the final active transform is dpr. Let me assert that the LAST setTransform call is (2,0,0,2,0,0).

Also "draws glyphs" threshold → lower to 100.

Let me fix these three in verify.js.

Two remaining:

1. "draws glyphs -> 76 glyphs" across 20 frames: heads start far above the screen (up to -720px) and move ~90-330px/s, so after 0.33s most are still off-screen. That's expected behavior (columns fade in from the top). The threshold was too high. But hmm — 76 glyphs over 20 frames = 3.8/frame. That's low but correct given the start positions. Let me instead run more frames (e.g., 120 frames = 2s) and check glyph count is substantial, and also check that the *conserved* structure is right. Let me run 180 frames (3s) and assert glyphs > 300.

Actually a more meaningful check: after enough time, all 56 columns should have entered. Let me run 600 frames (10s) and count distinct x positions drawn — should be ~56 columns visible over that window.

2. "post-resize draw transform" — the LAST setTransform is (1,0,0,1,0,0) because the last call in the log is from `clearCanvas()` inside resize (the identity clear). But `clearCanvas` does save() → setTransform(1) → fillRect → restore(), which restores the dpr transform. My stub's save/restore are no-ops, so the log's last setTransform is identity. The actual browser restores correctly. So this assertion is a harness artifact. I can make the stub track a transform stack to model save/restore properly. That's better: implement save() { stack.push(current) }, restore() { current = stack.pop() }, setTransform sets current. Then I can read the "current transform" and verify it equals dpr. Let me do that — it validates the real behavior including that restore() returns to dpr.

Let me restructure the ctx stub: maintain `current` and `stack`:

```js
function makeCtx(log) {
  let cur = [1,0,0,1,0,0], stack = [];
  const c = {
    log, fillStyle:'', font:'', ...,
    setTransform(...a){ log.push(['setTransform',...a]); cur = a.slice(); },
    save(){ log.push(['save']); stack.push(cur.slice()); },
    restore(){ log.push(['restore']); cur = stack.pop() || cur; },
    get current(){ return cur; }
  };
```
But `cur` needs to be exposed. Use `c.current` getter or return {ctx, getCurrent}.

Simpler: keep a module-level `ctxState = {cur, stack}` and assert on it. Let me restructure with an object.

Also need to verify: fillRect during clearCanvas uses full backing store. That passed.

Additionally, I want to check that the identity fillRect in clearCanvas happens in device pixels (it did: 0,0,1800,1000 ✓) and that draw() fillRect uses CSS pixels (0,0,900,500). Let me add that check too — it proves the transform is applied for drawing. With a transform-tracking stub, I can verify each fillRect/fillText coordinate space:
- clearRect in clearCanvas: device pixels, transform = identity at that moment.
- draw's fillRect: CSS px, transform = dpr.

Let me implement: record for each draw call the current transform. Then assert:
- The clear fillRect (0,0,1800,1000) happened with transform identity.
- Every fillText happened with transform (2,0,0,2,0,0).

That's a strong verification. Let me rewrite verify.js's ctx stub and add these assertions.

Let me also handle the glyph coverage check: run 600 frames and gather distinct x values.

Wait, there's an issue: the `textCalls`/`textAfter` filter changes shape since fillText now has extra entries at indices 4,5. Earlier lines use `c[2]` (x) and `c[3]` (y) — still valid. Good.

But the earlier `maxX = Math.max(...textCalls.map(c => c[2]))` still works.

Also the last check `textCalls = ctx.log.slice(-60000).filter(...)` then uses c[2], c[3] — fine.

Also I need to fix the "glyphs fit viewport" check after resize: it uses textCalls from a log slice taken BEFORE my new fillText entries have the transform. Fine.

Also note the resize check "resize clears whole new backing store" uses c[3]===1800 && c[4]===1000 — but now fillRect entries have extra '|t' at index 5,6,7. c[1]=0,c[2]=0,c[3]=1800,c[4]=1000 → still valid. Good.

Let me also add a distinct-column check to prove independent columns across the full width. Let me run and see.

Too many log entries with spread. Let me reduce frames to 120 and use a reduce-based max instead of spread.

326363 glyphs over 600 frames is ~544/frame across 56 columns ≈ 9.7 glyphs per column — hmm, that's the trail length average (8-30, avg 19). Wait, 544 glyphs per frame with 56 columns → 9.7 glyphs per column. That means many columns are still off-screen or... hmm, average trail length is 19, so a fully-visible column draws ~19 glyphs. 56*19 = 1064. We got 544, so about half the columns are off-screen at any time? That seems like a lot.

Hmm, wait. Consider: heads start at rand(-height*0.9, -fontSize). A column's trail occupies head..head+len*fontSize. With speed ~90-330 px/s (avg 210) and height 800: time to traverse from -720 to 800 is up to (1520/90)=16.9s for the slowest, ~7s for fast ones. Average cycle maybe 10s. During the cycle, the column is on screen for roughly (800 + len*22)/speed seconds ≈ (800+420)/210 = 5.8s out of ~10s → ~58% visible. Plus at boot, columns are spread over the initial -720..-22 range so they enter staggered. That matches ~544/1064 = 51%. Reasonable.

OK so the logic is fine. Let me reduce the frame count and use safe max computation.

Interesting: `active=[2,0,0,2,0,0]` is correct, yet the check `lastST[1] === 2 && activeTransform[0] === 2 && activeTransform[3] === 2` FAILED. Hmm: lastST is the last setTransform entry, which is (1,0,0,1,0,0) from clearCanvas → lastST[1] = 1, not 2. So the `lastST[1]===2` part fails. That's expected — the last setTransform call is the identity clear inside save/restore. The active transform is correct (2). So drop the lastST part of the check; the important thing is the active transform.

The second failure: "all glyphs drawn with dpr transform — offenders=502". These are fillText entries from BEFORE the resize (in CSS space 1200x800 with transform (1,...)). I filter all fillText in the whole log rather than just post-resize ones. The `textCalls` in that check uses the whole log. I need to only consider glyphs drawn after the resize. The log order: entries before the resize marker. I can find the index of the last setTransform with value 2... Simpler: snapshot the log length right before running post-resize frames, then filter entries after that index.

Let me restructure: after `flushTimers()`, record `const mark = ctx.log.length;` then after frames, filter `ctx.log.slice(mark)`.

Also note: the clearCanvas fillRect in resize has '|t' identity, which is expected (device-pixel clear). I'll exclude fillRect from that check and assert separately that the identity-space fillRect covers the full backing store (already checked).

Let me fix.

The offenders check: `c[4][0] !== 2` — the fillText log entry is `['fillText', t, x, y, '|t', cur.slice()]`, so the transform is at index 5, not 4! I wrote `'|t'` at index 4 and the array at index 5. Fix: use c[5].

Also `post-resize glyphs fit new viewport` uses maxX=645 — because only columns that entered so far. Fine (the check is `maxX <= 901`).

Let me fix the index.

All automated checks pass. Now let me also verify pause/restart behaviors programmatically in the harness, and also verify the button click handlers work (since the browser click didn't seem to register — I should investigate whether it's a harness/tool issue or a real issue).

Let me test in the harness:
- The pause button element's addEventListener registration — my fake element records nothing. I should record listeners so I can invoke them. Let me extend the fake element to record click listeners, then simulate a click on pauseBtn and restartBtn, and assert the rAF loop stops (no more frames) and that the canvas is cleared.

Also I need to model `requestAnimationFrame`/`cancelAnimationFrame` to know if the loop is stopped: after pause, calling `step()` should not queue new frames.

Let's add:
- `el()` gets `listeners: {}` and `addEventListener(type, fn)` storing them.
- Simulate `els.pauseBtn.listeners.click()` → then `advance(1/60)` and check no frame callbacks run.
- Then simulate click again → resume: frames run again.
- Simulate restart click: assert clearCanvas happened (a fillRect with full backing store right after) and columns rebuilt (statCols unchanged count) and no stale glyphs remain: check that the log's last fillRect is the full-screen clear, and that subsequent draw calls only contain fresh glyphs.

Also test keyboard handlers (space, r, p) via the window keydown listener.

Let me add a second test section to verify.js. Since the app's internal `columns` isn't accessible, I can check that after restart the drawing only draws glyphs for reinitialized columns... Hard to check. But I CAN verify the clear happened: a fillRect covering the full canvas, and that glyph drawing after restart has different x positions (rebuilt layout with same pitch though). Hmm, simplest: verify clearCanvas full-screen fillRect happens immediately upon restart, and that the frames continue (running) or stay frozen (paused).

I could also check memory growth: "no accumulating off-screen state" — the column count stays constant (already verified over 400s of simulation).

Let me add the interactive section.

Also note: for the pause check in the harness, `statState.textContent` should be 'paused' and `pauseBtn.textContent` 'Resume'.

Let me write it.

I need to make the fake element record click listeners. Let me update the `el()` function in verify.js.

Two failures:

1. "Pause button stops the animation loop" — the condition includes `aliveAfterPause === 0`. But `aliveAfterPause = framesQueued()` measured AFTER `btnClick('pauseBtn')`... Let me look: 

```js
btnClick('pauseBtn');
const aliveAfterPause = framesQueued();
```
So aliveAfterPause is 0 (correct, since cancelAnimationFrame in my stub doesn't actually remove... wait, my cancelAnimationFrame is a no-op! So the queued rAF callback stays in rafQueue. Hmm, but framesQueued() returned 0 — because `step()`/`advance()` splices the queue each time, so after the last advance the queue is empty; the next frame is only queued when the previous frame callback runs. So after pause, no new callbacks are queued → 0. Good.

So why FAIL? Maybe `els.pauseBtn.textContent === 'Resume'`? Let me print the values. The condition is:
`els.statState.textContent === 'paused' && els.pauseBtn.textContent === 'Resume' && framesQueued() === 0 && aliveAfterPause === 0`

The stats textContent is set via `statState.textContent = 'paused'` — yes. Hmm, but wait: `statState` readout is `<div>state <b id="statState">running</b></div>` — I set `statState.textContent = 'paused'` — that works on my fake element.

Hmm, but earlier in the test I did:
```js
if (!els.statState.textContent.startsWith('running')) btnClick('pauseBtn');
```
The state at that point: 'running' (from boot) — unless something changed it. The console printed "controls: state=running label=Pause fps=60" → correct.

So after btnClick('pauseBtn'): state should be 'paused', label 'Resume'. Then `framesQueued()`: at that moment, has a frame been queued? After the last `advance(1/60)` in the loop of 60, the frame callback re-queues itself via requestAnimationFrame → so rafQueue has 1 entry! So `aliveAfterPause === 1`, not 0.

Wait but I measured aliveAfterPause AFTER the pause click: pause() calls cancelAnimationFrame (no-op in stub) → queue still has 1 → framesQueued() = 1 → `aliveAfterPause === 0` fails. And the later check `framesQueued() === 0` — after `advance(5)` twice: advance runs the queued callback → frame() → but `if (!running) return;` → returns without re-queueing → queue becomes 0. So framesQueued()===0 passes but aliveAfterPause==1 fails.

So the assertion `aliveAfterPause === 0` is wrong — the correct assertion is that after pause, the queue drains and no new frames are requested. Let me fix: assert that after two advances, framesQueued() === 0 (already covered) and remove aliveAfterPause.

2. "R restarts while paused": condition `framesQueued() === 0 && els.statCols.textContent === '61'`. Before that, `key(' ')` twice → paused. Then key('r') → restart. framesQueued() should be 0 (paused). statCols = '61'. Hmm, so why fail? 

Wait — the keydown handler: `else if (e.key === 'r' || e.key === 'R') { restart(); }`. My `key(k)` builds `{code: k===' '?'Space':'', key:k}`. For ' ', code='Space' → first branch toggles. Then for 'r': code='' → falls to `e.key === 'r'` → restart(). Should work.

Hmm, but the preceding step: `key(' ')` — pause. Then `key(' ')`... wait the sequence is:
```
key(' ');  // space toggles -> running
report('Space resumes', ...)  PASS
key(' ');  // pause again
report('Space pauses', ...)  PASS
key('r');  // restart while paused
report('R restarts while paused', framesQueued() === 0 && els.statCols.textContent === '61')  FAIL
key('p');
```

Hmm, so framesQueued() must be 1? No — we're paused, so nothing queues... unless the pause happened and then the frame callback... no, we're not calling advance.

Wait: after "Space pauses", is the state truly paused? Yes (PASS). So restart() while paused → no rAF. framesQueued()===0. And statCols '61'.

Unless `els.statCols.textContent` isn't '61' at this point! Note: restart() → buildColumns() → `statCols.textContent = String(count)` where count = ceil(width/pitch)+1 with width=900, pitch=15 → 61. Unless resize() ran... no.

Hmm, but wait: in my harness, W=900, H=500, DPR=2 were set earlier, and the canvas width is 1800 — but statCols was verified as '61' in the earlier "Restart keeps column layout count stable" PASS. So statCols is '61'.

So the failure must be `framesQueued() === 0`. Hmm, why would frames be queued while paused? 

OH! I see — `key(' ')` toggles. Before "Space resumes", the state was... let's trace: "Restart while paused redraws a fresh (cleared) frame" → then "still paused after restart-while-paused" → state paused. Then `key(' ')` → resume → running → rAF queued = 1. Then `key(' ')` → pause → cancelAnimationFrame (no-op) → queue still has 1! So framesQueued() === 1 → FAIL.

Right — my stub's cancelAnimationFrame is a no-op, so the queue retains the pending callback. The correct assertion is "no NEW frames are requested after pause": i.e., after advancing twice, the queue is empty. Let me restructure the assertions:

- After pause: `advance(2)` → queue should be 0 (loop stopped).
- For "R restarts while paused": assert `framesQueued() === 0` AFTER draining: advance(2) then check 0.

Let me fix both. I'll implement a helper `drain()` that advances twice and returns the remaining queue length.

Also make cancelAnimationFrame actually remove the pending frame to be more faithful:

```js
let rafId = 0;
requestAnimationFrame(fn) { rafQueue.push({id: ++rafId, fn}); return rafId; }
cancelAnimationFrame(id) { const i = rafQueue.findIndex(q=>q.id===id); if(i>=0) rafQueue.splice(i,1); }
```
And step() should call `q.fn(ms)`. Let me restructure: rafQueue entries {id, fn}. `framesQueued()` returns length. cancelAnimationFrame removes matching id. That's faithful and then `framesQueued()===0` right after pause works.

Let me implement that.

All automated checks pass, including button click handlers (so the buttons DO have working click handlers; the browser tool's click coordinates just missed the buttons).

Now let me go back to the browser and try clicking the buttons again with better coordinates. The earlier click at (80,30) and (75,25) didn't work. Maybe the harness's click uses a scaled coordinate system: the page might be displayed at a different scale. Let me test by clicking at a position and observing. I know the button's visual location: In the screenshot, HUD "MATRIX RAIN Pause Restart" spans from x≈14 to x≈200, y≈20..36. Pause button center ≈ (78, 28).

Hmm, wait. Maybe the browser tool's click coordinates are for a viewport that is 1200x800 but the actual iframe content is rendered with a device pixel ratio or scaled... Let me try clicking at (100, 40), (60, 20), etc. Or maybe the harness click requires the page to be focused and it clicks at viewport coords of the top-level page, where the iframe is positioned at some offset (e.g., if the iframe is smaller than the window, there's an offset).

Since the keyboard events DO reach the page (space worked!), the harness has focus on the iframe. So a click at (80,30) should hit the button if coordinates map 1:1.

Let me look at the screenshot image dimensions... The images appear to be 1200x800 based on the canvas readout matching. Let me try a few clicks at slightly different positions and check the state via the DOM readout (each click result includes the dom text). I'll try (78,28).

Actually — maybe the issue: the button's clickable area. `#hud` has `display:flex; gap:10px; padding? no`. The buttons have padding 5px 12px, font 13px. "MATRIX RAIN" with letter-spacing 1px ≈ 11 chars * ~8.7px ≈ 96px + margin-right 4 → HUD content: title 96 + gap 10 + Pause button (~50) ... Pause button starts at x≈120 and ends ≈170, center ≈145! Wait, the title "MATRIX RAIN" is 11 characters at 13px monospace ≈ 7.8px/char = 86px + letter-spacing 11px = ~97px. Starting at x=14 → ends at 111. + gap 10 → Pause button spans x≈121..170. Center ≈ 145, y≈28.

I clicked (80,30) and (75,25) — those are ON THE TITLE "MATRIX RAIN" text, not on the button! That's why nothing happened. My coordinate estimate was wrong.

Let me click at (145, 28).

Also the Restart button: spans ≈180..245, center ≈212, y 28.

Let me click Pause at (145,28).

The Pause button click works: state paused, fps 0, button label "Resume".

Now let's test the Restart button click at ≈(212, 28) and confirm trails clear.

Also I notice the rain is quite dense/thick in the browser (many glyphs). Looks good.

Let's click Restart.

Restart while paused cleared the screen completely (all old trails wiped) and remained paused. 

Now let me resume via the button and confirm the animation restarts from scratch with fresh trails. Then do a final visual check.

Click Resume (145,28).

State is running (fps 0 because it just resumed and the fps stat updates every 0.25s). The screen is black right after restart — expected since columns start above the viewport.

Let me do one final check: wait a couple seconds and take a screenshot to confirm the rain refills, then finalize. The file is already saved (index.html). I should also remove the verify.js helper? The task says write everything to index.html; extra files are fine but let me keep the workspace tidy — I'll leave verify.js (harmless) or delete it. Better to remove it to keep only index.html, but it documents verification. The addendum says "End with index.html present." I'll keep index.html and delete the temp verify script to avoid confusion... Actually keeping it is harmless and shows verification. I'll delete it since the deliverable is a single self-contained file.

Let me do the final screenshot first.

The rain refilled after restart+resume, running at 60fps. Effects verified:
- Multiple independently moving columns ✓
- Brighter leading glyphs (visible as brighter glyphs, e.g. "ﾌﾑ", "ﾎ", "ﾃ") ✓
- Fading trails ✓
- Varying speed/length ✓
- Pause/Resume/Restart buttons ✓ (verified in browser + harness)
- Resize verified in the harness ✓

Let me finalize: remove the temp verify.js (and dbg files are in /tmp, not the cwd) to leave a clean deliverable. Actually, verify.js is in the cwd — I'll delete it to keep the deliverable clean per "End with index.html present".

Let me confirm index.html is intact and self-contained (no external refs).