Matrix digital rain · deepseek-v4.1-flash

Let me build this. I'll create the index.html file, then test with browser tools.

Let me write a solid Matrix rain implementation.

Key features:
- Full-screen canvas, black
- Columns of katakana glyphs
- Each column has a head (bright, white-ish/green) and fading green trail
- Vary speed and start position
- Recycle after leaving bottom
- Pause/Resume and Restart with buttons
- Responsive resize without stretching (redraw at proper DPR)

Let me write it carefully.

I'll use fixed font size (e.g. 16px), column width based on font size. Each column tracks y position in rows or pixels.

For fade trails: I'll use the classic approach of drawing semi-transparent black rect over whole canvas each frame, then draw new glyphs. But that can leave residue. Alternative: per-column store a list of glyphs and draw full trail each frame. To "recycle after leave bottom" and clear, easier to keep per-column trail.

Let me do per-column arrays of characters with positions. Each column has an array of glyphs from top (head) going up. Actually typical: a column occupies a vertical run. As it moves down, the head advances; behind it trail fades.

Approach: Each column has `y` (head pixel row in cells), `speed` (cells per frame), `length` (trail length), and an array of characters for each trail position. When head moves, add new char at head, shift.

Draw each frame: clear black, then for each column draw each trail cell with alpha based on index, head bright white.

This is clean and no accumulation. Recycle: when entire trail passes bottom, reset y to negative random start.

Let me implement with requestAnimationFrame and delta time for consistent speed.

Column height: number of rows = floor(canvasHeight / fontSize). Columns count = floor(canvasWidth / fontSize).

Each column: 
- headRow (float)
- speed (rows per second)
- trailLength
- chars: array indexed by trail offset, length = trailLength
- when integer part of headRow changes, shift chars: new char at head, drop oldest.

Simpler: track headRow as float. On each frame advance. Determine current head cell = floor(headRow). If head cell advanced, push new char(s) at front.

Let me represent trail positions as pixels rather than cells to be smooth. Actually simpler to draw glyphs at cell positions.

Let me store: col.y = head y in pixels. col.speed px/s. col.trail = array of {char, y}. Each frame, move all trail y down by speed*dt? No—the trail should follow head. Better: store head y, and trail is derived: trail[i] drawn at y - i*fontSize. chars stored. When head crosses into a new cell (floor((y)/fontSize) changes), insert new random char.

So:
- col.y += speed*dt
- col.cell = Math.floor(col.y/fontSize)
- while col.lastCell < col.cell: unshift new char to col.chars; col.lastCell++; trim chars length to trailLength.
- Draw: head at col.y bright; then for i in 1..chars.length: draw chars[i-1] at col.y - i*fontSize with alpha fade.

Wait head char should be chars[0] perhaps. Let head char be drawn at col.y with bright white, and chars[0] is the most recent past head? Let me just: chars[0] is the glyph at cell col.lastCell. Draw head glyph (the newest) at col.y. Then trail uses chars.

Actually to make the bright leading character, draw at col.y the glyph = col.currentChar (newest). Behind it, previously generated chars at positions col.y - i*fontSize with decreasing alpha.

Reset when col.y - trailLength*fontSize > canvasHeight, i.e., whole trail off screen: reset col.y = random negative, new speed, etc.

Let me code it.

Font: use monospace fallback, "MS Gothic", "Hiragino Kaku Gothic", monospace. Katakana range U+30A1-U+30F6 plus some. Half-width katakana maybe to be monospace. Use full-width katakana; set textAlign center.

Handle DPR: canvas.width = innerWidth*dpr, style width 100%. ctx.scale(dpr,dpr). Recompute columns on resize but preserve existing where possible. Requirement: "Resize the canvas and column layout to fit viewport without stretching old screenshot or leaving uncovered strip." On resize I'll recompute width/height and column count. I can preserve existing columns that fit and add new ones. To be safe, on resize rebuild? "without stretching an old screenshot" means resizing canvas reallocates backing store, so no stretch. I'll re-init columns on resize (or preserve). Simpler to rebuild columns but that clears trails—acceptable on resize. But better preserve. Let me preserve columns: keep columns array, adjust for new count. Recompute fontSize? Keep fixed fontSize. Rows change.

Actually to avoid "uncovered strip", ensure canvas fills window and column count covers width.

Let me include controls fixed at top, with Pause/Resume toggle and Restart button. Also maybe show FPS? Not needed.

Pause: stop rAF, keep state. Resume: restart loop with lastTime reset.

Restart: reinit columns, clear canvas.

Let me write the file.

Also console errors check.

Let me write.

For animation loop I'll use a running flag.

Draw background: instead of fillRect with black every frame (which clears), since we draw full trails each frame, just fillRect black. Good.

Alpha fade: alpha = (1 - i/trailLength) maybe with head extra bright. Use rgba(0,255,70,alpha). Head: white-ish #c8ffd0 or #eafff0.

Let me also make glyph flicker: occasionally change chars. Optional. Add subtle.

Now write file.

Now let's run it in the browser and inspect.

Mostly empty. Only a tiny bit at top. The screenshot seems to be rendered at a larger resolution than the browser viewport? The canvas is 1200x800 CSS but the screenshot is 1500x1000 or so? Actually image looks scaled.

The issue: the columns start mostly above the viewport (y negative), so initial frames mostly empty. Also the trail is drawn but maybe glyphs are faint. Wait there's a glyph at top around x=700. After some time more should appear. The screenshot was taken at frame 1 (0ms). Maybe browser screenshot captures the first frame. Let me wait and take a motion frame.

Actually the fact only top edge shows glyphs suggests columns are moving down but screenshot taken very early. Let me use motion action to sample several frames.

The screenshots show almost nothing except top edge glyphs. The animation isn't progressing/drawing. Wait, the frames all look identical. That's suspicious - maybe the requestAnimationFrame isn't running in the headless browser's screenshot capture? Or maybe draw is happening but glyphs are off-screen.

Actually the top edge shows a few glyphs at y near 0. The columns start at y between -cssH*0.5 and 0, so after moving down they should be visible quickly. But in 1.7 seconds at 60-260 px/s they should move 100-440px, definitely visible. Yet screenshots look static.

Hmm, maybe the issue is that `resize()` is called and it calls `draw()` before `start()`. Then start() begins rAF. But frames 2-4 all look identical. Maybe the browser tool captures screenshots at almost the same instant? The motion shows +556ms, +1107ms, +1693ms.

Wait, maybe the canvas is actually 1200x800 but the screenshot is 1200x800. The glyphs at top are around x=700,830,920,990. In all frames they appear at same place. So animation frozen.

Why? Let me check: `start()` sets running=true, then requestAnimationFrame(frame). frame checks `if (!running) return;`. Good. dt computed. Then advance. Should work.

But wait: in `resize()`, `ctx.setTransform(dpr,...)`. Then draw fills 0,0,cssW,cssH. Fine.

Hmm, but maybe the browser screenshot tool renders the page in a way that rAF doesn't advance unless the page is visible? It did produce motion frames though.

Actually maybe the problem: `colCount` unused. Fine.

Let me look more carefully. Potential bug: GLYPHS katakana may not render (font missing) and show nothing? But we see glyphs at top. Actually they may render as boxes. 

Wait — maybe the issue is that columns are being recycled too fast or reset every frame. In `advance`, recycle condition: `col.y - col.trailLength * FONT_SIZE > cssH`. Not triggered early.

Hmm, why frozen? Let me test by inspecting the canvas state via JS maybe. I can't run arbitrary JS directly, but the browser inspect only returns DOM text. Let me check the screenshot timestamp. Could be the tool captures the same cached frame due to no compositor updates? Possibly the headless browser doesn't repaint canvas during motion capture unless... but it did show frame 1 with a glyph and frames 2-4 same.

Let me try clicking pause and then resume, and take screenshots. Also let me use browser action to evaluate? There's no eval action. Hmm.

Maybe the issue is that rAF in headless with no display only fires when snapshot requested, and the timing gaps cause dt clamp to 0.1. That's fine; positions should still change.

Wait, actually look: frames 2,3,4 identical but frame around top has glyphs at slightly different positions? Let me compare: all have glyphs near top x=700,830,920,990. They look identical.

Let me reconsider: maybe draw() is filling black each frame but columns' y hasn't changed because `advance` isn't being called — perhaps an exception in the loop stops it. Console shows empty though. Let me check the code for errors.

`var colCount` declared, fine.

In draw, `col.x` is set in advance. On the very first `draw()` call from `resize()` (before start), col.x is null so we set it. Good.

Hmm `frame` function: `rafId = requestAnimationFrame(frame)`. fine.

Wait — maybe the problem is `resize()` is called on every... no.

Let me check: is it possible that window.innerWidth/innerHeight at the time of resize is 0 or small? No, buttons render.

Actually, the key clue: there ARE glyphs at the very top in all frames. If columns started within [-cssH*0.5, 0] = [-400,0], after ~0.5s they'd be at -400..+130. Many still above 0 but some visible. But they'd progress. Unless speed is being reset every frame? No.

Let me reconsider: On the very first screenshot (frame 1) we saw one glyph at top. Then motion frames show 4 glyphs at top. So it DID progress a little between frame 1 and frame 2 (more glyphs appeared). Then frozen between 2-4. So maybe rAF only fired a few times.

Hmm. Possibly the headless browser suspends rAF but the motion capture advances timers? Actually rAF might be throttled. But then dt clamp 0.1 each frame gives slow movement. Between frame2 and frame4 (1.1s) maybe only 1-2 rAF fires, each dt=0.1 → 10-26px movement. At 18px font, head moves ~1 cell. Might look similar.

Let me test more robustly: click pause, screenshot; then wait via motion; screenshot should be identical if paused. Actually we can't easily tell.

Better: let me add a debug that writes column y into the DOM so inspect can show it. Or simpler, test by increasing speed? No.

Actually the real question: does it work in a real browser? The implementation logic seems sound. But the screenshots suggest columns aren't appearing across the screen. Let me think about why after 1.7s so few glyphs.

Oh! I think I see. The issue is DPR. `window.devicePixelRatio` in this browser might be >1, and the canvas backing store is larger, but CSS size is set correctly. That's fine.

Wait, another thought: maybe columns that are off-screen above are being drawn but `gy` checks. Fine.

Hmm, let me reconsider the initial distribution. `makeColumn` with startAbove=false: `y = rnd(-cssH*0.5, 0)`. For cssH=800, y in [-400,0]. Trail pre-filled length ~6-24. Head at y, trail above at y - t*18. So entire visible area only shows columns whose head reached >0. After 1.7s at speeds 60-260, avg 160*1.7=272px. So columns starting at -200 would be at +72, visible. Many should be visible with trails. But we see only 4 glyphs total.

This strongly suggests the animation ran only a tiny bit (dt small). Perhaps rAF is heavily throttled in this environment. The motion capture may not actually wait real time between frames.

Given the 15-min budget, let me verify functionality more directly by instrumenting: I'll add a temporary DOM element showing frame count and a sample column y, then use motion/inspect. Actually inspect returns DOM text, so I can read it. Let me add a hidden debug div updated each frame.

Actually there's a simpler explanation: maybe requestAnimationFrame is not firing at all after first few, and the motion tool's frames are timers. Let me check by making the animation loop also use setInterval fallback? No, better to first diagnose.

Let me add a debug overlay with frame counter. Then reload and inspect after a delay.

But wait—maybe the real problem is that the canvas isn't being captured in screenshots and what we see at top is... Actually the glyphs at top look like they're at y≈0, partially cut. That's consistent with columns just entering.

Let me instrument.

The dbg element isn't visible in screenshot (bottom left). Only a few glyphs at top. Interesting - only a handful of columns visible. There are ~66 columns (1200/18). Most should be somewhere.

Wait, I see glyphs at x≈460, 900, 1090 near top. These look like half-width chars. The dbg text at bottom-left isn't shown, maybe it was overwritten by canvas? No, z-index 20 and position fixed. But canvas is position fixed too. dbg appended to body after canvas, z-index 20 > canvas. Should show. Unless the screenshot was taken before dbg updated — but it's created at script load.

Hmm the dbg appears absent. Maybe the screenshot omits it because... Actually the UI buttons show at top. dbg at bottom should show. Not there.

Let me inspect DOM text.

DOM text doesn't include dbg, meaning dbg wasn't added or frame loop never ran to update text. Wait dbg is created and appended regardless. inspect returns dom as text content of body — it shows "PAUSE\nRESTART" only. That means dbg is empty and maybe not captured in innerText (empty divs produce nothing). Since frame never ran, dbg.textContent stayed ''. That means requestAnimationFrame is NOT firing at all!

And the glyphs at top come from the initial `draw()` call in resize(), which draws columns at their starting positions (some just at top). So rAF never fires in this headless capture environment. That's why the animation appears frozen.

So the animation logic might be fine but rAF isn't running in the tool. Hmm, but the task expects us to verify animation frames. Maybe rAF does run but the screenshot tool freezes time. The "motion" action should capture across time. It produced frames but identical.

Perhaps requestAnimationFrame is disabled/throttled because the page is considered hidden in headless. A common workaround: use setInterval or setTimeout-driven loop, or drive rAF but also render. Actually many headless environments do run rAF.

Let me test with a simple setInterval counter in dbg to see if timers run. I'll change loop to use setTimeout fallback. Actually, to be robust for both real browsers and this tool, I could drive with requestAnimationFrame but also set up a setInterval fallback? That could double-advance in real browsers.

Better: detect. Hmm. Simpler robust approach: use a rAF loop, but if rAF doesn't fire within e.g. 500ms, fall back to setInterval. But complexity.

Actually, maybe rAF fires but the tool screenshot is taken at t=0 before frame. The dbg being empty after "Frame 1 +0ms" is expected since first frame may not have run. Let me call motion and see if dbg text changes. But motion screenshots are taken and inspect isn't called. Let me do motion then inspect.

Actually earlier motion frames showed slight progression (frame1 one glyph, later 4 glyphs) — that suggests some frames ran between reload and motion. Then it froze. Hmm.

Let me just test timers. Change dbg to update via setInterval too. Actually let me add a setInterval that increments and updates dbg, independent of rAF. Then inspect after motion.

Let me do a quick diagnostic: add
setInterval(function(){ dbg.textContent = 'iv=' + (++iv); }, 200);

But then if both update dbg they conflict. Let me make dbg show both. I'll add a separate counter.

Actually, I recall pi's browser tool likely freezes rAF to allow deterministic screenshots? Not sure. Let's just test.

Let me modify dbg to include an interval-based counter.

Now dom shows iv=1 f=0. So interval fired once (or is at 1) but frames=0. rAF hasn't run. Let me wait with motion and inspect again to see counters.

Confirmed: setInterval advances (iv 11→21) but frames f stays 0. So requestAnimationFrame never fires in this headless capture. That's an environment limitation. But to make the app verifiably animate in this tool (and still robust in real browsers), I should drive the animation with a timer fallback, or just use setInterval/rAF hybrid.

Best approach: use requestAnimationFrame when available but detect if it's not firing and fall back to setInterval. Or simpler: drive with a rAF loop, plus a watchdog setInterval that calls the frame if rAF hasn't fired recently. But that could double-render.

Actually cleanest for verification: use `setInterval` at ~60fps (16ms) as the main loop. It works everywhere including this tool, and is perfectly fine for this animation. Some might prefer rAF, but setInterval is acceptable. However, setInterval in background tabs throttles; not a big deal.

To be safe and smooth, I'll use rAF with a setInterval fallback that only runs when rAF is stalled. Simplest robust: 

- Keep rAF loop.
- Add setInterval(check, 100ms): if document visible and (now - lastFrameTime > 100ms) then manually call step().

But double stepping risk minimal if synchronized. Better: single loop driven by rAF, and fallback interval calls step only if rAF hasn't fired in > 200ms. Once rAF fires, interval steps would still run because lastFrameTime updates each rAF, so interval condition false. Good.

But simpler and guaranteed: just use setInterval(step, 1000/60) entirely. It animates fine. I'll go with a hybrid: I'll use rAF and setInterval fallback? Let me keep it simple and reliable: use setInterval-based ticker. Actually many Matrix demos use setInterval. Let me switch main loop to setInterval(16). But pause must stop it, resume restart it.

Let me restructure:
- tick() computes dt from performance.now, advances, draws.
- loop = setInterval(tick, 16) when running.
- pause clears interval.
- start sets interval.

This will animate in the tool. Let's do that. Remove rAF.

Also I should remove debug code at the end, but keep during testing and remove before final? The debug overlay is extra. I'll remove it in final.

Actually, to verify, I need it now. Let me switch to setInterval and keep debug for now.

Let me edit.

At frame1 +0ms, the interval hasn't fired yet. Let me wait a bit via motion then screenshot/inspect. Use motion to let time pass.

Now the canvas is completely black across all 4 frames. The debug overlay also isn't showing. That's strange. And no glyphs at all now. Did setInterval run? The dbg element should show something at bottom left once frame runs. It's not visible. Console empty.

Wait, is the script erroring now? Console shows empty. Hmm. If script threw before resize/start, canvas would be black and dbg maybe created. dbg.textContent set only in frame. But dbg should appear as empty (invisible). Not shown.

But why no glyphs from resize's initial draw()? Because maybe an exception occurred before resize. Let me check the code — I removed `start()`'s rAF but ensure `resize()` then `start()` at the bottom still. Also `restart()` references rafId? No. Let me re-read the file end.

Actually potential bug: `frame(performance.now())` inside setInterval. Fine.

But the complete absence of initial glyphs suggests script threw early. Let me read the file to verify.

I see the bug: at the bottom it calls `resize()` then `start()`. But `start()` begins with `if (running) return;`. `running` is initialized to `true` at declaration! So start() returns immediately and never sets up the interval. Previously with rAF, start() also would return... wait originally running=true and start() returns, so rAF was never started either! That's why f=0. Then how did the initial glyphs appear? From resize()'s draw(). 

So the earlier absence of animation was partly due to this bug, not the environment. Let me fix: initialize running=false, or set running=true in start unconditionally.

Also the current black screen: after I switched to setInterval, resize() draw() should still show glyphs at start positions. But it's black. Why? Because columns start at y in [-cssH*0.5, 0] and trails above, so heads near 0 or negative; at draw time only a few glyphs at top. Earlier we saw those few. Now entirely black — maybe because makeColumn randomness gave all heads well above 0 for that particular run. Actually with random y in [-400,0], on average heads spread; but draw only draws head if y in (-18, 800). Probability a head is in (-18,0) is 18/400≈4.5%, so ~3 columns. Trail also. So a few glyphs expected. Could be zero on a given run. Fine—not a real problem once animation runs.

Wait but earlier screenshots showed glyphs at top; the trail check `gy < -FONT_SIZE` continue. So only visible ones. OK.

Fix running bug: set `var running = false;` initially. Then start() sets running=true and interval. Let me do that.

Also remove debug later. Let me fix now.

Now it's animating: f=12, y0=-206. We see bright leading glyphs (white) with green fading trails at top. But only at the very top; the rest of screen is empty. This is because after 12 frames (~0.4s), most columns still above. Wait y0=-206. Many columns should be across. After 0.4s at avg 160px/s = 64px. So heads from -400+64=-336 to -64. Still above 0 mostly. So only the few whose start was near 0 show. That's fine, but it means the screen takes a while to fill. The requirement says vary start position; not necessarily prefill. But for a good initial look, columns should be distributed with heads across the screen initially, not all above. Better: start y distributed across full range from -cssH to cssH (some already on screen). Let me make initial y = rnd(-cssH, cssH*0.5) or so. Actually to have a fuller screen immediately, distribute y uniformly across [-trailLen*FS, cssH]. Since trail drawn above head, if head at y, trail extends upward. So to fill screen, heads should be spread from 0 to cssH. Let me set initial y = rnd(0, cssH) for a mix, plus some above. That gives immediate full effect and still varied starts.

Requirement: "Vary column speed and start position." So random start across screen is good.

Let me change makeColumn initial y to rnd(-cssH*0.2, cssH) maybe. And pre-fill trail. Since trail is above head, a head at top has trail above (off-screen), so column looks short. That's normal.

Better approach: think of each column as having a "head" and trail above. If head is at 100px, trail occupies 82,64,... Above. Looks like a falling stream. Good.

For full coverage, random heads across [0, cssH]. Yes.

Let me update makeColumn and resetColumn accordingly. resetColumn(above) for recycling should start above top so streams re-enter naturally: y = -rnd(FS, cssH*0.5). Good, keep.

makeColumn (initial) startAbove false currently -cssH*0.5..0. Change to rnd(-cssH*0.25, cssH).

Also note initial draw in resize before start shows distribution. Good.

Let me also address: after fix, animation works. Now remove debug overlay eventually. But let me first make the change and verify full-screen rain, pause/resume, restart.

Let me edit makeColumn.

Now the full Matrix rain appears: multiple columns, green glyphs, fading trails, bright leading glyphs (some white at bottom of trails). The trails look a bit long and the head is at the bottom (bright). Actually the bright glyphs appear at the bottom of each trail, which is correct for falling rain. Good.

Wait, the trails look quite long (full column height in some cases). trailLength max 24 * 18px = 432px, about half screen. Fine.

Now test pause/resume and restart. Let me capture current state, click Pause, capture after motion, compare; then Resume and confirm movement; then Restart confirm reset.

But debug overlay persists. I'll keep for verification but should remove at the end.

Let me test pause. Click pause button at (54,31).

Button now RESUME, and f=224 frozen. Good. Now let me wait/motion and check that frame count stays same and image frozen, then resume. Let me do motion and inspect.

Pause confirmed: f=224 constant and all four frames identical. Good. The rain looks great — independent columns with bright leading glyphs (some white/gold at the head, e.g., "G", "L", "H") and fading green trails.

Now test Resume. Click the RESUME button.

Resume works: f went from 224 to 238+, button back to PAUSE, and the image changed (columns moved). Good.

Now test Restart. Click Restart button (~154,31).

Restart cleared old trails (screen black except a few glyphs at very top). But note: Restart resets columns with `resetColumn(col, false)` which places y = rnd(-cssH*0.5, 0), so all columns start above screen again, giving a mostly empty screen briefly. That's acceptable for "resets the columns and clears previous trails," but the earlier requirement also says vary start position. It might be nicer for restart to redistribute across the screen like the initial state rather than all above. The task says "Restart resets the columns and clears previous trails." Starting fresh is fine. But a fully empty screen for ~1s is less visually pleasing. 

I think a better restart redistributes heads across [-0.25h, h] like initial, so it looks like a fresh shower with coverage. "Clears previous trails" is satisfied because draw() fills black and new columns have pre-filled trails in random positions. Let me change restart to use the same initial distribution. I'll make resetColumn take an option or add a `fresh` mode. Simpler: in restart, call makeColumn-like reset with distributed y. Let me modify resetColumn signature: resetColumn(col, above) where above=false distributes across screen. But recycling uses above=true. The current resetColumn with above=false uses rnd(-cssH*0.5,0) — change that to rnd(-cssH*0.25, cssH) to match initial. Then restart uses resetColumn(col,false) → distributed. Recycling uses resetColumn(col,true) → above. 

Let me update resetColumn's non-above branch.

Also I should remove the debug overlay for the final version. Let me do both edits.

One more consideration: the requirement "Recycle columns after they leave the bottom so the effect continues without accumulating off-screen state." Our recycle resets col and re-generates chars; array length stays bounded (trailLength). Good.

Also "Resize the canvas and column layout to fit the viewport without stretching an old screenshot or leaving an uncovered strip." We set canvas.width/height to cssW*dpr and redraw everything. Good. Let me test a resize if the tool supports it—there's no resize action. I can verify by reasoning and maybe by checking devicePixelRatio. The browser viewport is 1200x800; canvas covers full. Let me check computed canvas size via inspecting? Not available. Fine.

Let me make the edits.

Also the restart function has a useless early return branch: after draw(), if !running return; else lastTime=0. That's fine but let me simplify - it's harmless.

Now reload and verify: full rain, no debug overlay, restart gives distributed fresh state. Let me reload and inspect console.

Now full-screen rain immediately on load, no debug overlay. Bright leading glyphs clearly visible at the bottom of trails (white/bright, e.g., "W", "B", "C"). Fading green trails. Independent columns at different positions and lengths. 

Let me do a final motion sample to confirm independent movement, then a restart to confirm distributed fresh state. Actually I already verified restart behavior but after change I should re-verify. Let me take a motion (multiple frames) to see movement, then click restart and screenshot.

The motion frames confirm independently moving columns with varying speeds, bright leading glyphs (white/bright at bottom), and fading green trails. Looks great.

One observation: some trails are extremely long (spanning nearly full screen) because trailLength up to 24 * 18px = 432px. That's fine. But in frame 4, some columns' trails seem to extend from top to bottom (maybe recycled ones). Fine.

Now verify Restart gives a fresh distributed state. Click restart.

Restart gives a fresh, fully-populated screen with new random positions, speeds, and glyphs — old trails cleared. 

Everything looks good. Let me verify the final file has no debug remnants and is valid. Let me grep for dbg/frameCount/rafId.

No debug remnants. Clean. Let me do a final read of key sections to ensure correctness, particularly the loop and the restart function, and check that the early-return in restart is okay.

Actually one thing: restart when running does `lastTime = 0;` which means next frame dt = now - 0? No: `if (!lastTime) lastTime = now;` so dt=0 then lastTime=now. Fine.

Also on `start()` after a pause, lastTime=0 → dt=0 first frame. Fine.

Everything verified. Let me quickly confirm the file top and structure once more? Not necessary.

Let me also double check no external resources. The code uses only local fonts and no URLs. Good.

I'm confident. Final report.

Actually let me reconsider the recycle logic potential edge case: if a column's speed is high and dt clamped 0.1, it could skip many cells; the while loop adds one char per cell. Fine. If speed*dt is huge (e.g., 260*0.1=26px, ~1.4 cells). Fine.

One more: `advance` sets col.x each frame. Good.

Done. Report.