Boids flocking · qwen3.8-27b

Let's build the app.

Let's test in the browser. Note: if the page is blank, nothing will be drawn — no problem.

The boids are nowhere to be seen. The screenshot might be a frame where they're all drawn extremely small, but... if there are 150 triangles of about 7px, they should be visible. Something might be wrong — maybe an exception is being thrown before draw? The console only shows sandbox warnings. Hmm. Is the canvas being drawn behind? Or is the clear/fill after the triangles? No, the fill comes first. Let me check for errors — inspect the console further, or run a quick check in the browser to see whether the boids are on screen. Actually, maybe the screenshot is being taken at frame 1 before any rAF step has happened, and the boids should still be visible. Let me click somewhere to trigger pointermove, and then take another screenshot to check the console.

The boids aren't visible, and the cursor circle isn't showing either. The pointer should be inside (already clicked). Hmm — is the canvas being drawn but the boids just invisible? A 14px hsl triangle should definitely be visible. Maybe there's a JS error after the init? But the console is only showing sandbox warnings. Wait — is it possible that the exception happened but the console display is getting truncated? Let me try inspecting the DOM / canvas width.

The boids aren't visible, but there are no JS errors either. Suspicious points: is draw() being executed? The canvas background is being filled (dark color). The boids should be drawn with hsl color... could it be that the screenshots are being taken before rAF runs? But it's 150 triangles — they should definitely be visible. The canvas size is zero, or the drawing is... no, the background is being displayed (dark navy, not pure black — the background color #0b0e17 is the body's; the canvas fill is the same color, so I can't tell them apart).

Possible bug: is the canvas's CSS `position: fixed; inset: 0` with display block, with style.width/height also set. No problem there.

Hmm, wait — maybe an error is occurring in step() and rAF is halting, and draw() isn't being executed either. If it's an exception inside frame(), that should show up in the console as an error. I don't see any errors.

Maybe the screenshot tool is capturing before the first frame. But even the click at +0ms was before the frame? "Frame 1, +0ms" — each browser tool call might be reloading, or capturing a new snapshot at +0ms. In fact, each call shows "Frame 1, +0ms", suggesting a fresh capture every time. But the boids are drawn every rAF, and after the first frame they should persist.

Let me try debugging with a different approach: I can't run JS in the browser tool... there's no JS evaluation action. Hmm. The available actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. Can't evaluate JS directly.

Let me try "motion" to see the animation frames.

The screen is pitch black (dark navy). No boids are visible. Could it be that the canvas is behind the body's background? No — the canvas is fixed, with position specified, and it should render on top of the body's background. If the boids are being drawn, they should be visible.

Possible issue: the canvas is being rendered, but is a script error preventing rAF? No, there are no errors in the console. Or... maybe the screenshot is capturing the page, but the canvas is transparent and the boids are being drawn — no, that can't be.

Wait: maybe `requestAnimationFrame(frame)` — the first call is `requestAnimationFrame(frame)` passing `now` — that's fine.

Hmm, one thought: in the sandbox environment the canvas is being drawn, but the screenshot might be using `toDataURL`... no, that's not it.

Let me think: could there be a subtle JS error being swallowed? The console only shows sandbox warnings. If step() throws an exception, frame() gets interrupted and errors would be shown in the console.

Actually — could the browser tool's screenshot be capturing the DOM but not the canvas contents (a common issue in headless environments where canvas is blank without preserveDrawingBuffer or a WebGL flag)? This tool's "images" capture might be rasterizing only the DOM and leaving the canvas blank. But the dark background — body's background is #0b0e17, and the canvas's fill is also #0b0e17. That would be consistent with the theory that the canvas isn't being rasterized in the screenshot.

To distinguish, change the canvas's fill to a different color (e.g., #141a2e) and add a static bright rectangle test... actually there's an easier way: draw a big bright circle at the center in the initial draw, take a screenshot, and if it shows up then the canvas is being rendered. Let me change the background fill to something distinguishable, like "#101527" or so, and see if the canvas area differs from the body.

Actually, let me just add a temporary debug: fill the canvas with a bright color. If the screenshot still shows the dark background → the canvas isn't being captured (tool limitation) and I can't visually verify, but the code is probably fine. If a bright color shows → the drawing code has a problem.

Let me test with a bright fill.

The edit tool interpreted the content strangely — did it insert `\r` characters?? My edit JSON contained \r characters — I made a mistake when writing the edit (I accidentally included \r characters). The tool actually did the replacement (it shows success). Let me read the file and check what state it's in.

Weird — the file looks fine (no \r is visible). The edit must have worked normally (probably the \r characters were normalized, or the matching succeeded). Let me check the draw section.

The file looks correct (no \r). Alright, let me reload and take a screenshot.

Even the red rectangle in the center isn't showing up. In other words, one of the following:
1. The screenshot tool doesn't rasterize the canvas, or
2. A JS error is occurring before the first draw (rAF doesn't fire / an exception gets thrown), so the draw isn't executing.

The console shows no errors. If the exception were inside rAF, an error should show up in the console. The script runs at load time: resize(), reset(), requestAnimationFrame(frame). If any of these synchronously throws an exception (e.g., inside resize), a console error should appear. I don't see any.

Hypothesis: the tool's screenshot doesn't capture the canvas contents (a common thing in DOM-only screenshots; though in headless Chrome screenshots usually do capture the canvas). Or, rAF doesn't fire in a hidden/background tab — but if the tab were hidden, the animation should be paused, and the canvas should be blank (nothing drawn yet, transparent). The first draw is inside frame(), which only runs when rAF fires. If rAF doesn't fire, the canvas is blank/transparent → the body's background shows through. This fits!

But the motion tool captured frames at +548ms etc., so time is passing; rAF should fire in headless Chrome unless the page is occluded or rAF is being throttled.

The safest fix: draw once synchronously after init (call draw() directly), don't rely on the first rAF. This guarantees the canvas has content immediately. Additionally, if the rAF-driven loop is throttled, the screenshots should show a static flock — in which case we can't fully verify the animation, but the presence of the boids can be confirmed.

Let's add draw() after the init. Also, keep rAF for animation. If the motion frames still don't change, it's throttling; we could add a setInterval fallback? Better yet: use both requestAnimationFrame and a 60ms setInterval fallback? That could cause double-stepping. Simpler: keep rAF, and also call draw synchronously once.

Actually, to be more robust in a throttled environment, we could drive the loop with setInterval(fn, 16) instead of rAF. setInterval in background tabs is throttled to 1 second or more, but it fires. Let's do this: keep rAF as primary, but the first draw is synchronous. For the simulation, if rAF is throttled to 1 second, the motion frames at +548/+1075ms will be almost static (with the dt clamp f<=3, only one step per second). This would make "coordinated motion" hard to verify visually.

Alternative: use setInterval(frame, 16) instead of rAF — in a background tab it's throttled to 1000ms. Hmm, headless Chrome often runs pages in the foreground, so rAF should be fine. Let's first try the synchronous draw() and check whether the boids show up.

Wait, I've used those weird \r escapes again, but it worked fine before — the tool seems to be normalizing them. Actually, it's more likely that the tool is matching while ignoring \r. It's working, so I'll continue, but let me confirm that the file isn't corrupted.

Alright. Now let's reload and take a screenshot.

Even the red 40x40 debug rectangle at the center is not displayed, even though draw() was executed synchronously. That means the canvas drawing exists, but it's not being reflected in the screenshot... or the canvas element isn't positioned where I think it is (1200x800), or there's a possibility the screenshot is simply not rasterizing the canvas.

Another possibility: there's no canvas in the DOM, or it's hidden? In the DOM text, only the button and info are shown. Could it be that the canvas has zero size? window.innerWidth should be 1200. canvas.style.width is being set. Hmm.

Wait — the reason the screenshot isn't showing the canvas is because of CSS `position: fixed`... no, fixed elements get rendered in screenshots.

Let me test: I'll add a red border to the canvas via CSS. If the red border doesn't appear, then the canvas element isn't being rendered at all (probably hidden or zero-sized). If the border appears but the inside is empty, then the drawing isn't being reflected in the screenshot (a tool limitation).

It looks like the editing tool is inserting a literal \r character?? When I actually read the file earlier, there were no issues with $ line endings (cat -A shows only $, no ^M). It's possible that \r's in the JSON are being interpreted as carriage returns and are being handled... The earlier grep showed clean content, so this is probably fine. Let me quickly check the file for any CR characters.

Alright, no CR characters. Reload.

Now I can see the red outline — the canvas is being rendered, but the size is small! The red box is roughly in the range x: 0 to 300, y: -20 to 155. So W and H are not 1200/800. canvas.style.width = W + "px", where W = window.innerWidth. The viewport is 1200x800, but in this sandbox maybe window.innerWidth is around 300? Wait, the red outline extends slightly beyond the left edge (x from -20 to 300?). Actually the right edge is around x=300, and the top edge is above the top of the screen (y < 0). If the outline is inset:0, then the canvas should be positioned at (0,0) with size W×H. Right edge is 300 → W ≈ 296? And the top edge goes off-screen → does y start from a negative value? inset:0 sets top:0. The top edge looks like it's around y=-40... hmm, maybe it's actually starting from y=0 and the outline's thickness is... no, the top red line isn't visible. The top of the red line is around y=0 but off-frame? In the image the red vertical line goes from the top edge (y=0) down to about y=155, and the horizontal line is at about y=152. So the canvas is roughly 300×155.

So window.innerWidth ≈ 300? But the screenshot is 1200×800. Maybe the browser tool is taking the screenshot at 1200×800, but the actual window/iframe size is different, e.g. 300x155? Hmm. Or devicePixelRatio... no, that's not it.

Probably the iframe's viewport is small (300x155) and the screenshot is being scaled up or padded. Either way, the fix is: my code is already resizing based on window.innerWidth/innerHeight on load and on resize events. But if the actual size is 300×155, the canvas should fill that... the red outline matches 300×155 within a 1200×800 screenshot. So the viewport really is about 300×155 CSS px, and the screenshot is either scaled or the page has been zoomed.

Wait, but the HUD buttons and text look normal size relative to the 1200×800 screenshot. If the page were 300px wide, the buttons should appear larger. Unless the screenshot is scaled up by 4x, in which case the text should look 4x larger and blurry. The text looks crisp at normal size.

Alternative explanation: canvas.width = W*dpr, canvas.style.width = W. With W=300... no, that's not it.

Hmm, could it be that `window.innerWidth` returned something weird? For now let me try displaying it: I can't eval JS. But I can add a DOM text element that displays innerWidth/innerHeight to check. Or, more simply: remove the debug, and additionally add a window 'load' + setTimeout resize, and use document.documentElement's size as a fallback.

Let me add a debug: set document.title = W + 'x' + H and read it... the DOM dump might not include the title. I can set info.textContent to include the dimensions.

Wait — that edit: I've once again written \r all over the place. It looks like the tool is doing some weird conversion on my input. But the previous edit matched without issue. Something in my pipeline is converting \n to \r\n, and then the tool is normalizing it back. Whatever, let's just go with it.

No, wait — I'm the one who wrote \r in the edit JSON! That's my bug: I'm literally outputting "\r" into the parameter. The tool apparently normalizes \r to \n on match. Alright, let's just proceed as is.

Reload, and read the info text.

Two discoveries:
1. The info text is still displaying the old string — meaning the change to my textContent in resize() isn't being reflected, i.e., the script errored out before that line, or resize() hasn't executed... but wait, the red canvas outline is still showing up (300x155), so resize() must have been executed previously. But my textContent change is before the return path... actually, textContent is now set after W/H are calculated. If an exception occurred before that (e.g., getElementById("info") is fine)... hmm, or is the page being cached? The DOM still shows the original info text. If resize ran, the text should be "WxH dpr=". It's not — so either resize threw an error before setting the text, or the script failed at parse time (in which case the canvas outline comes from CSS, and the canvas stays at its default 300x155!).

That's it! A default canvas is exactly 300×155! So the script is failing at parse/execution time — probably a syntax error introduced by my \r edit. The CSS outline is showing, and the default canvas size is 300×155. So the script has never run even once! That would explain the blank canvas from the start, with no boids. But there are no console errors... weird, but maybe console capture is incomplete.

Wait, but in the earlier DOM dump the info text was displayed as-is — consistent with the script not having run at all.

Why would there be a parse error? The \r I inserted — my edit JSON contained literal \r escapes, and the tool apparently wrote... let me check the actual bytes of the file. The earlier grep -c $'\r' returned 0, so there are no CRs. Hmm, but that grep was from after the second edit. And the file contents looked fine in the read output.

Wait, actually — could it be that the script is failing because of the \r I typed inside the edits[] JSON? The tool wrote it, grep says there's no \r. OK.

Let me look for syntax errors: node --check the script portion. I'll extract the JS between <script> and </script> and run node --check.

The syntax is OK. So the script parses. Then why isn't resize() running? Let me test execution with node (simulating a DOM-less environment won't work). Let me run it in a near-headless way: use node with a minimal DOM stub, or better yet, if jsdom is available? Probably not installed.

Alternative: the script might be throwing an exception at runtime (an exception inside resize, or before that). For example `document.getElementById("canvas")` is fine. `ctx = canvas.getContext("2d")` is also fine.

Actually wait — maybe the script is running fine, but the browser is caching the old file? The first load was before the debug edits… no, I've reloaded many times since then, and the red outline (a new edit) did show up, so the reload is loading the new file. The red outline edit and this edit are in the same file version… actually, the outline was added in the previous edit, and the resize() debug is in this edit. Both should be in the current file. But the info text hasn't changed.

Hold on — maybe resize() is throwing an exception at `document.getElementById("info").textContent = ...` — no, that's fine.

Hmm, is the script running but failing partway through, before resize? Order: function declarations, then at the bottom: resize(); reset(); draw(); rAF. If `draw()` or something throws, resize is called first and the info text should have changed. It hasn't.

Could it be that… the script is running and changing the text, but the DOM dump is reading a cached value? Unlikely.

Let me check the whole file again — could it be that my edit containing \r inserted literal characters in a weird way and broke the structure, leaving multiple script tags or duplicated blocks behind? Let me look at the resize function and the end of the file.

The file contents appear correct. But the page isn't reflecting this (the info text hasn't changed). So the browser must be serving a cached/old version of the file! The red outline showed up... wait, when did the outline first show up? After the outline edit was reloaded. And the outline is from the edit before the info debug. So the version the browser is serving contains the outline but not the info change? Both were separate edits: (1) debug fill, (2) init draw(), (3) outline, (4) info debug. The current screenshot has the outline but no info text update. If caching had stopped at version 3, that would be consistent.

Maybe the browser tool is caching the file (ETag?). Let me try adding a query parameter... I can't control the URL. I'll try reloading one more time.

The info text still isn't updating. In other words, the script really isn't executing that line. Given that the syntax is OK, the script must be failing at runtime before resize() — or the script isn't running at all. If the script weren't running at all, the red rectangle inside draw() shouldn't be visible... it isn't visible. Consistent with the script not running at all.

Why wouldn't it run? Perhaps the browser tool is loading a cached version from before the debug edits — but in that case, even that old version's script should run and... the old version's info text matches the original. Hmm! The served version might be the original file (before the debug fill), and the outline... no, the outline edit was inside the CSS. If it's the original version, the outline shouldn't be showing.

Wait, maybe the served version is version 3 (with the outline), and the reason the info text isn't updated is because the script failed at runtime. What could fail in version 4 (current file)? Syntax is OK... but wait, did node --check pass on the current file? Yes, I extracted it from the current file.

So in the current file: the script should run, resize() should set the text. It isn't being set. Unless an exception is being thrown before it: `pauseBtn.addEventListener` etc. are fine. Actually wait — an exception inside `buildGrid`/`step` would only show up in the console as an error. The console is clean.

Maybe the page being served is really an old copy. Let's test: modify the info text in the HTML itself (statically) to "VERSION5" and reload. If the DOM shows VERSION5, then the served file is fresh.

Hmm, wait, this sed is a replacement for `<div id="info">150 boids`—in the original source, this div is written as `<div id="info">150 boids &middot; ...`. No problem.

The file is being delivered freshly (VERSION5 is displayed), yet resize() isn't updating the info text (it should become "WxH dpr=" and replace the text). So the script is failing at runtime before that point in resize(), or it isn't running at all. But no console errors are showing up...

Wait — maybe the console is only capturing messages from a specific source. Or maybe an error is occurring. Let's check: the script runs in the body... `document.getElementById("info")` works. What's failing?

Let's trace it: I'll write a small Node test using a DOM stub to check for runtime errors. No, simpler: let's add error reporting to the page: wrap the init in try/catch, and output the error into a DOM element (since console messages might not be visible... though they should actually be visible). Let me add a window.onerror handler that writes to the info div.

The \r character seems to be automatically converted to \n (the previous grep didn't find any \r). No problem.

Reload.

Still no errors displayed, no changes to the info text, and the red rectangle is missing. In other words, the entire script block isn't being executed (if it were, the "WxH dpr=" text would be displayed, and an error would be caught).

Hypothesis: Is the browser tool serving the HTML through a pipeline that strips out `<script>` tags? No—the original file had a script, and the red rectangle... wait, the red rectangle was never visible. The only thing that got rendered was the CSS outline. So it's highly likely that either the script content is being stripped/sanitized, or the script is failing at parse time (syntax errors are fatal, and in some browsers they don't fire window 'error'... no, actually they do fire). Hmm, but maybe my onerror handler is also in the same script, so if the script has a parse error, the handler isn't registered either.

Let me test: extract the exact bytes of the script block and verify whether node --check can still parse it now (after the latest edits). Also, let's check whether the file is using weird Unicode characters. Let me dump the hex of the beginning portion of the script.

The JS file is syntactically valid and clean. Therefore, either the script tag isn't being executed in the browser tool's environment, or... wait. Could it be that the browser tool's screenshot/DOM is coming from an iframe, and scripts are being disabled? The sandbox warning mentions the "allow-scripts" sandbox attribute—if the sandbox has allow-same-origin but **not** allow-scripts, then scripts won't execute! The warning says "both allow-scripts and allow-same-origin"—so both are present, and scripts should execute.

Hmm. But the evidence: the script never runs. Let me test with a dead-simple experiment: replace the entire script with just `document.getElementById("info").textContent = "SCRIPT RAN";`.

No Python 3. The script hasn't been modified. Let me check whether node exists (it does, I just used it). I'll do the replacement with node.

node -e failed silently? No output, exit 1. Probably because the quotes got messed up by the shell. Should I write a node script to a file and execute it, or just use node to directly rewrite the entire index.html as a minimal test — an easier way: write a minimal index.html with the write tool, then restore from backup afterwards.

Still failing. Is node unavailable? Earlier, `node --check` output SYNTAX_OK, so node does exist. But `grep -n "SCRIPT RAN"` returning exit code 1 means there was no match, so the replacement wasn't performed. Could it be that node /tmp/repl.js silently failed? No, the && chain: node succeeded, and then grep failed. Let me check the contents of index.html.

Line 69 only has `<script>` — where's `</script>`? Did my regex `<script>[\s\S]*<\/script>` not match because `</script>` doesn't exist?! But in the earlier `awk '/<\/script>/'`... the reason the awk extraction worked earlier was because it output everything after `<script>` all the way to EOF. Wait, the earlier awk was `/<script>/{f=1;next}/<\/script>/{f=0}f` — if `</script>` doesn't exist, it would output from line 69 to EOF. Let me check the end of the file.

The file ends with `})();` — the `</script>`, `</body>`, and `</html>` are missing! It seems the last edit (adding onerror) truncated the end of the file. The onerror edit replaced `<script>\n(function () {` — but wait, the file previously ended with `</script></body></html>`. Hmm, actually, the original write ended with `</script></body></html>`. Let me verify: was the original file intact? The onerror edit should have only touched the top of the script. But now the file ends with `})();` with no closing tags.

Something truncated the tail. Whatever the cause, this explains everything: no `</script>` means the script never gets parsed, and HTML5 treats the rest as a script up to EOF… actually, an unterminated script would consume up to EOF as JS — but the JS is complete, and an implicit script end at EOF is tolerated, so the script should actually execute… hmm, in practice browsers terminate a script at EOF. The code should work. But the missing `</html>` is weird.

Whatever the cause — the simplest path: rewrite the entire file cleanly with `write`, removing the debug elements (keeping the synchronous `draw()` at initialization, but removing the debug fallback, the red rectangle, the outline, the onerror, and the VERSION5).

I made a typo: `function limitY(vy, max) { return vy > max ? max : (vy < -max ? -max : vy; }` — the bracket isn't closed, and moreover I'm not even using these limitX/limitY functions! I'll delete them.

Check whether the file ends properly, and also check the syntax.

I also want to quickly verify the step logic headlessly. Let's run the extracted JS in node using a small canvas/document stub, and confirm that there are no runtime errors and that the boid coordinates stay in a finite range.

The 'info' element was never created (the script doesn't touch #info — correct, no error handling that touches info currently exists). So it's a bug in my harness. The important thing is that eval + 120 frames ran without throwing. Good — 120 frames executed without a runtime error.

Better test: expose the boids and verify that movement is coordinated. Can I modify the source before eval, replacing `})();` at the end of the IIFE with `})(); globalThis.__get = function(){return boids;};`? The IIFE closes scope... `boids` is in the IIFE's scope, so the assignment to globalThis has to be inside. Replace the trailing `})();` with `window.__boids = boids; window.__paused = function(){return paused;}; })();`.

Results so far:
- 150 boids, all finite, average velocity is aligned (meanV is non-zero → coordinated movement, aligned).
- Spread is close to the entire screen (with 150 boids in 1200×800, it's expected that they disperse. meanV shows alignment).
- Pointer test: after 5 seconds only 2 boids were within 120px of the center (the flock was elsewhere), and 0 fled. Should improve by placing the pointer at a location with boids.
- Pause test failed. Because the click capture in the harness was performed after the addEventListener call had already happened during eval (the listener is registered first, and my override was performed later, so the original addEventListener is a noop). A different approach is needed: capture the listener via the stub from the beginning.

Let me fix the harness: save the listener in the el stub: addEventListener saves the handler into el._handlers.

Results:
- Escape behavior: only 4 out of 31 escaped — weak but it's working. The problem: boids near the centroid might be moving toward the pointer's direction of motion. The force exists but is weak. Acceptable, but the test metric (distance > +1px over 30 frames) — a boid moving away at ~3px/frame should pass easily. 4/31 suggests that many boids were moving nearly tangentially, or that the flee force is weak. MOUSE_FORCE 0.25 × (0.5+t) × force cap MAX_FORCE*3 = 0.24/frame vs. speed 3.2 — acceleration is small relative to speed, so it takes about 15 frames to reverse direction. Over 30 frames it should mostly escape. The ones that didn't escape were probably moving tangentially. Well, acceptable.

- Resumption of movement: false — a concern! After the pause button was clicked, frames(60) → no movement? Wait, the button text shows "Pause" after the second click, so paused=false. But s2===s3? s3 is after the resume click but without a frames() call! I computed s3 immediately after the click without stepping. My bug: I didn't run frames between s2 and s3. So "resumed moves: false" is a bug in my harness, not a bug in the code. Right: after `click('pauseBtn'); const s3 = ...` — no frames. So it's a false negative.

- Order parameter 0.57: moderate alignment — no problem, it's being coordinated.

Remaining time is 5 minutes. I'll quickly verify resume in the harness, and do one browser screenshot to confirm visual rendering. Then I'm done.

Confirmed that Resume works. Next, check the browser visuals — reload and take screenshots of several moments.

150 triangles are now displayed, with different orientations and speed-based colors, and the dashed circle for cursor influence appears near the pointer (upper-left, pointer is at approx. (75,20)).

Next, I'll check the motion frames for coordinated behavior, pointer repulsion, and pause/resume in the browser.

Excellent! Clear flocks forming, triangles aligned to their direction of motion, moving coherently across frames — flocking is clearly working.

Next I'll test pointer interaction: drag/click toward the center of the flock (around 900, 300) to make it scatter, then verify pause/resume. Click (600,400) — pointer circle appears, nearby boids flee.

Pointer at (950,350) — you can see the dashed influence circle, and the boids at its edge have been pushed out: the flock is clearly avoiding the circle (there's a gap around the circle's boundary, and the boids are bending around it).

Next, I'll test pause: click the Pause button and take 2 screenshots to confirm it's frozen, then resume.

The button currently displays "Resume" — pause has been enabled. Beautifully organized flock (strongly aligned, all triangles pointing in the same direction). Note: The pause click also moved the pointer to (41,32), so a radius is displayed at the upper left, but since it's paused there's no response.

Confirming that the simulation is frozen while paused: take screenshots twice with a time gap between them. Since the "motion" action might step rAF even during the pause (draw is executed but step is not), the positions should be identical. Use the screenshot twice.

Completely identical to the previous frame — the simulation is frozen during pause. Next, I'll resume and confirm that it continues.

The button shows "Pause" (already resumed). Since this screenshot was taken immediately after the click, the flock still appears to be in roughly the same position. Let's take one more screenshot to confirm that it's moving again.

After resuming, the flock continues smoothly to the lower right, maintaining its alignment. All required behaviors verified:

1. ✅ Flocking: The flock forms, moves in a coordinated manner (order parameter 0.57; visible coherent motion in the frame), and triangles point in their direction of movement.
2. ✅ Speed/steering constraints: Smooth motion across frames, no teleportation; verified via numerical harness (finite, bounded).
3. ✅ Cursor repulsion: The flock curves around the dashed 120px radius, and a gap forms; the harness shows boids escaping; confirmed flock reformation after resumption (within 200px, 123/150).
4. ✅ Pause/Resume: While paused, pixel-identical frames; resumes on Resume and continues; button label toggles.
5. ✅ Reset: Verified via harness (N=150, finite).
6. ✅ Resize: resize() recalculates size and clamps boids; the window resize listener redraws when paused. Not visually verified in the browser (no resize tool) — the code path has been run in the harness (resize was called at initialization).

Time check: About 4 minutes remaining. Final state is good; the file is the final version. Done — writing up the report.