Force-directed graph · mimo-v2.5

Let me look at the directory first.

Let me check the d3 version.

D3 v7.9.0, includes d3.zoom, d3.drag, d3.forceSimulation.

Design:
- 40 nodes, 4 clusters of 10. Rings within cluster: node i connects to i+1 (mod 10) within cluster →10 links per cluster ×4 = 40 links. Hub ring: 0-10, 10-20, 20-30, 30-0 → 4 links. Total 44 links.
- Force simulation with link, charge, center, collision.
- Zoom via d3.zoom on svg, transform on a g. Drag nodes via d3.drag on node group, but must convert coordinates correctly: since the g is transformed by zoom, d3.drag gives event.x/y in the local coordinate system of the element being dragged (because d3.drag uses the container's screen->local transform). Actually d3.drag by default uses `container` = parent node of the element, and transforms pointer events through the parent's CTM. So if nodes are inside the zoomed g, dragging automatically accounts for zoom. But the sim nodes positions are in the g's local coordinates which is what we want. Good. But careful: I should set drag subject to node, and set fx/fy in local coords. d3.drag gives event.x/event.y in parent coordinate space (the g), which matches node.x/node.y. Good.

However, background pan: attach zoom to the svg; but node drag needs to stop propagation of zoom. Use `event.sourceEvent.stopPropagation()` in drag start. d3.drag's start event already stops propagation? Actually d3.drag calls `view.on("dragstart.drag"...)` and it stops propagation of the underlying pointerdown? Let me recall: d3-drag's mousedown handler calls `nopropagation` on the event when it selects... In d3-drag, `started()` does `if (drag.disableClick ...)`. Hmm. Standard practice: in drag `start` handler, `event.sourceEvent.stopPropagation()`. Yes, in many force-directed examples (e.g., "La Manna force-directed graph"), they don't need it because zoom is on svg and drag on node with `event.sourceEvent.stopPropagation()`. Actually d3-drag's gesture start calls `selection.on("start.drag", ...)`; the mousedown handler in d3-drag does `if (dragDisable ...)` — I recall d3-drag's `mousedown(event)` does `if (!event.ctrlKey ...) { view.on(...) }` and it calls `event.stopPropagation()`? Let me check d3-drag source: 

```js
function mousedown(event, ...args) {
  if (touchending || !event.ctrlKey) {
    var view = ...;
    gesture("start", event, name, ...);
  }
}
function gesture(type, event, view, datum, name, ...) {
  ...
  if (!view.on("drag." + name, dragged).on("end." + name, ended)) ...
}
```
Hmm, in d3-drag v3:
```js
function mousedown(event, that, args) {
  if (touchending || !event.ctrlKey) {
    var view = select(event.view);
    gesture("start", event, pointer(event, that), that, args);
 ...
    view.on("mousemove.drag", dragged, ...).on("mouseup.drag", ended, ...)
    dragDisable(event.view)  // captures pointer
 ...
  }
}
```
And dragDisable captures the pointer which prevents zoom's drag events from firing? d3-zoom uses its own mousedown handler; both handlers on svg/node. Since event bubbles, node's mousedown triggers d3-drag, and it stops propagation? d3-drag's gesture start calls `emit(type + "start")` which... In d3-drag source, `function gesture(type, event, view, datum, name, ...) { ... view.on("drag." + name, dragged).on("end." + name, ended); ... }` I believe d3-drag does call `event.stopPropagation()` somewhere: in `started()`: `if (dragging) { ... }` Hmm.

The safest is to explicitly call `event.sourceEvent.stopPropagation()` in the drag start handler. That prevents the event bubbling to the svg zoom handler. But if the mousedown on the node bubbles to the svg before drag's handler processes... stopPropagation in dragstart (called synchronously in the same event dispatch) does prevent further bubbling. Good.

Also zoom filter: allow zoom only for wheel and left-drag on background. Default zoom filter excludes right-click and ctrl+wheel. Fine.

Reset view: store initial transform identity (k=1, x=0, y=0) — but "keep the initial graph within view" — I'll set initial transform based on viewBox. Simplest: use viewBox fixed to a coordinate space matching width/height at load (e.g., 1200x800), force center at (600,400). Then zoom transform starts at identity, and reset calls `svg.transition().duration(750).call(zoom.transform, d3.zoomIdentity)`.

Better: make the SVG fill the container, use a fixed viewBox "0 0 1200 800" with preserveAspectRatio. Zoom works in screen coords though — d3.zoom's transform is applied in the coordinate system of the element... d3.zoom transform applied to g; zoom's pointer coordinates are computed via pointer() on the target which accounts for SVG transforms including viewBox. So zooming works fine with viewBox.

Hmm, but there can be subtle issues with d3.zoom + viewBox in some browsers — generally fine.

Alternative simpler: no viewBox, use width/height from container and center force at (w/2, h/2), update on resize. I'll do that: on resize, update center force and re-center? But resizing also should keep graph in view. Let's just compute width/height from container and update simulation center force; on reset also reframe.

"Reset view to restore the initial camera framing without replacing the graph data." So reset just resets the zoom transform (and maybe also repositions camera, not the node positions). I'll capture the initial framing transform (identity, but maybe we fit the graph). To keep it simple and deterministic: initial framing = identity, with forceCenter at center of viewport, and node positions within radius ~ half. To "keep the initial graph within view", I could run a few pre-simulation ticks and then fit. Simpler: set initial random positions in a small disc around center and rely on charge/link forces. And also do `simulation.stop()` with initial ticks? Let's do: set x0/y0 for each node deterministically in a disc radius 150 around center, tick simulation 100 times before rendering (with forceCenter), then draw. That guarantees initial layout in view.

Actually with40 nodes and charge strength -240, the layout spreads to maybe 600px diameter. Fine for a 1200x800 viewport.

Let me also add a legend showing cluster colors, a title, and a Reset view button. Maybe a "Reheat" button isn't required. Also highlight behavior.

Labels: text labels with node id, drawn next to node circle. Keep in the same g.

Hover highlight: on mouseover of node group (or circle), set classes: dim non-neighbors, keep neighbors and links incident. Implementation: add class 'highlight' to svg root; compute neighbor set; add 'faded' class to non-related links and nodes. Use D3 data joins with attribute/class function.

Let me write the code.

Structure:

```html
<div id="app">
  <header> title + buttons </header>
  <div id="chart"> svg </div>
  <div id="legend"> ... </div>
</div>
```

JS:

```js
const W = 1200, H = 800; // viewBox
```

Hmm, let me use actual pixel sizes with resize handling, no viewBox. But then testing with the browser tool at 1200x800 viewport — the chart height should be less than 800 due to header. Let's make layout: body full height, header ~56px, chart fills rest. Compute w/h from chart's clientWidth/clientHeight.

I'll implement:

```js
const svg = d3.select('#chart').append('svg')...
```

Zoom:
```js
const zoom = d3.zoom().scaleExtent([0.2, 8])
  .filter(event => { ... allow wheel and left-button background drag; but not on nodes since node drag stops propagation anyway })
  .on('zoom', (event) => { g.attr('transform', event.transform); g.attr(...) });
```
Also record transform for camera readout display (k, x, y) — nice for verification.

Drag:
```js
const drag = d3.drag()
  .on('start', (event, d) => {
    if (!event.active) simulation.alphaTarget(0.3).restart();
    d.fx = d.x; d.fy = d.y;
    event.sourceEvent.stopPropagation();
  })
  .on('drag', (event, d) => { d.fx = event.x; d.fy = event.y; })
  .on('end', (event, d) => { if (!event.active) simulation.alphaTarget(0); d.fx = null; d.fy = null; });
```
Note: "release lets the simulation settle" — clearing fx/fy on end lets it settle. Good.

Hover:
```js
function neighbors(d) { return new Set(adjacency.get(d.id)) }
nodeG.on('mouseenter', ...).on('mouseleave', ...)
```
Implement with classes:
```js
function highlight(d) {
  const nb = new Set([d.id]);
  links.forEach(l => { if (l.source.id === d.id) nb.add(l.target.id); if (l.target.id === d.id) nb.add(l.source.id); });
  nodeSel.classed('dimmed', n => !nb.has(n.id)).classed('faded' ...)
  linkSel.classed('dimmed', l => l.source.id !== d.id && l.target.id !== d.id);
}
function clearHighlight() { nodeSel.classed('dimmed', false); linkSel.classed('dimmed', false); }
```
CSS: .node.dimmed { opacity: .15 } .link.dimmed { opacity: .08 } .node.highlighted circle { stroke-width: 3; stroke: #111 }

Also on hover, the hovered node gets 'active' class → bigger stroke.

Mouse events on node group need pointer-events; labels too. Put drag on node group; mouseenter on node group. Note: during drag, mouseenter/leave could fire weirdly; acceptable.

Reset view:
```js
function resetView() {
  svg.transition().duration(650).ease(d3.easeCubicInOut).call(zoom.transform, d3.zoomIdentity);
}
```
"restore the initial camera framing" — the initial framing is identity (k=1,x=0,y=0) since coordinates are in the same space as viewport pixels. Good. But should reset also re-heat the simulation? No — must not replace graph data. I'll only reset camera. Maybe offer "Reset layout" too? Not required; keep only Reset view to avoid confusion. I could add a "Reheat" button but the requirement only lists Reset view. I'll add only Reset view (plus maybe a small note). Keep it minimal.

Camera readout: display "zoom: 100%, pan: (0, 0)" — helps verification.

Ticks: after creating simulation with nodes seeded, run `for (let i=0;i<200;i++) simulation.tick();` then simulation.stop() and render, then simulation.on('tick', ticked).restart() — Actually we want the graph to settle visually but start near-final. Run 150 ticks pre-render then let it run live (it will continue settling smoothly). Good.

Center force: use forceCenter(w/2, h/2) with node positions seeded around center; also forceX/forceY weak? Keep link + charge + center + collide.

Cluster colors: 4 colors: #4e79a7, #59a14f, #f28e2b, #e15759 (Tableau).

Cluster index: c = Math.floor(i/10).

Ring links within cluster: for c in 0..3: for k in 0..9: source = c*10+k, target = c*10+((k+1)%10).
Hub ring: [0,10,20,30] pairs (0,10),(10,20),(20,30),(30,0).

Note node 0 has degree 3 (ring neighbors 1 and 9, plus hub 10). Good.

Also add link distance maybe larger for hub links. Fine with uniform 60.

Let me also add "fit to view"? no.

Labels: use text with dy3.5, dx = radius + 4, and always visible (font-size 11). Or place labels centered inside circles? Radius ~9 with id up to 2 digits — font10 centered works. I'll place label to the right of circle, with paint-order stroke for readability.

Add a keyboard shortcut 'r' for reset? Optional, harmless.

Now, write the file.

Also handle resize: recompute w/h, update forceCenter, and if camera is at identity, keep. I'll just update forces.

Write file now.

There's a typo in CSS: `border-color: #3a4considerable;` — I accidentally wrote garbage. Fix it.

Also `svg.attr("viewBox", ...)` combined with zoom pointer coordinates — with viewBox set to pixel dims, and svg width 100% height 100%, viewBox maps 1:1 to pixels, so zoom coordinates fine. But if the viewBox is set to the same size as the rendered size, no scaling issue. However d3.zoom uses the svg element's client rect to compute; that accounts for viewBox. Fine.

Actually one issue: setting viewBox on resize may conflict slightly, but 1:1 so it's fine. Actually I could skip viewBox entirely. Keep it, harmless.

Fix the CSS typo.

Also ResizeObserver fires initially, calling resize() which sets alpha restart — fine.

Let me also check `#legend` position top:12px right, hud bottom left — fine.

Fix CSS.

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

But wait — the runner inlines d3.min.js; my script tag src="d3.min.js" is correct per instructions.

Let me test with the browser tool.

Note: the browser tool probably serves index.html from cwd. Let's reload and inspect.

The browser tool loads index.html presumably from the current working directory. Let's check with the browser tool - reload and screenshot.

Now let's run it in the browser and inspect. The browser tool runs index.html presumably from cwd.

No network anyway. The browser tool likely opens index.html directly. Let's use browser tool.

The environment may not have python or networking. Let's just use the browser tool which likely loads index.html from the working dir.

No python. The browser tool probably opens index.html directly via file path. Let's use the browser tool.

No python available. Use the browser tool to load the file directly.

The browser tool presumably loads index.html from cwd. Let's try reload and inspect.

Let's use the browser tool to open index.html. The browser tool presumably loads index.html from cwd.

No browser action tool available? The instructions say use browser tools. But my available tools are read, bash, edit, write. Hmm — "Run the application in the browser" but I don't have a browser tool in my function list. Only read, bash, edit, write. So I cannot actually launch a browser. Let me check if there's a headless browser available via node (puppeteer/playwright).

Playwright is available. Let me try to run the page in playwright to verify behavior.

No errors, 40 nodes, 44 links, 4 hub links. Now check that all nodes are within view. Let me screenshot and also test drag, pan, zoom, reset.

Let me write a test script.

Two problems:

1. **Node drag pans the camera.** After dragging node 5, camera became `translate(120,80) scale(1)` — meaning the zoom/pan handler fired during the node drag. The stopPropagation in drag's "start" apparently didn't prevent zoom's mousedown listener... Actually the issue: d3.zoom attaches its mousedown listener to the svg element; d3.drag attaches to each node `<g>`. The event order: mousedown on node → drag's handler (on the g, bubbling from circle). Both handlers run on the same event dispatch chain — the drag handler on the ancestor `g` runs first (bubble phase from circle to g), then the svg. stopPropagation should prevent reaching the svg. But d3.zoom uses `view.on("mousedown.zoom", mousedowned)` with capture? Let me check: d3-zoom's selection.on("wheel.zoom"...) uses "on" with the view (window/document). Actually d3.zoom adds listeners to the element: `zoom.on("wheel", wheeled)` internally registered via `selection.on("wheel.zoom", wheeled)`. And mousedowned on "mousedown.zoom". These are non-capture listeners on the svg element.

Hmm, but d3-drag's `mousedown` handler calls `event.stopPropagation()`? No — d3-drag's mousedowned calls `nopropagation(event)` which does `event.stopImmediatePropagation()` and `event.preventDefault()`. But d3-drag only does that if... let me check: in d3-drag, `mousedowned` calls `gesture("start", ...)` which calls `nopropagation`? Actually in drag.js:

```js
function mousedowned(event, that, args) {
  ...
  if (!filter.apply(this, arguments)) return; ...
}
```

Hmm. Let me look at d3-drag source. Actually in d3-drag:
```js
function mousedowned(event, that, args) {
  var view = select(event.view), ...;
  ...
  if (gesture("start", ...)) ...
}
```
Actually the important part: d3-drag's `dragstarted` calls `event.sourceEvent.stopPropagation()`? No. In d3-drag, the `start` handler gets a synthesized event; `event.sourceEvent` is the mousedown. d3-drag calls `nopropagation(event)` on the *synthetic* event when starting? Let me check source:

```js
function gesture(type, event, view, datum, name, container, dispatch, args) {
  ...
}
```

Let me actually read the d3.min.js or fetch d3-drag source from node_modules... not present. Let me just grep d3.min.js for "stopImmediatePropagation".

Actually the real issue may be different: my zoom filter. I filtered mousedown to allow background pan. But the drag on node fires "start" and I call stopPropagation on the sourceEvent. Yet camera moved by exactly (120,80) = the drag delta. That means zoom's dragmove handler ran, i.e., zoom's mousedown handler on the svg fired and started a pan.

Why did stopPropagation not work? Because d3-drag's mousedowned handler itself calls `nopropagation(event)` — but wait, my handler is the "start" listener of drag, invoked by d3-drag, and I call `event.sourceEvent.stopPropagation()`. That should stop the event from continuing to bubble to the svg. Unless... the listener registration order/element: the node `<g>` is inside `root` g inside `svg`. Bubble: circle → g.node → g.root → svg. Drag listener is on g.node. stopPropagation at that point stops it from reaching svg. So it should work.

Unless d3-drag's `mousedowned` is registered on the view (window) with capture, i.e., d3-drag uses `view.on("mousedown.drag", ...)` where view = the window, and it uses capture... Let me recall d3-drag source:

```js
function mousedowned(event, that, args) {
  var view = select(event.view), ...
  if (touchending || !event.ctrlKey) {
    ...
 gesture("start", event, name, ...)
  }
}
```
Actually d3-drag does: `selection.on("mousedown.drag", mousedowned)` — a bubbling listener on the node itself. And inside, when started it calls `view.on("mousemove.drag", dragged, {capture: true}).on("mouseup.drag", ended, {capture: true})` and importantly `dragDisable(event.view)` which captures pointer events to prevent text selection — it sets `document.body.style.userSelect` etc. and importantly does NOT stop the mousedown from propagating.

Hmm wait — actually d3-drag's `mousedowned` DOES call `event.stopPropagation()`? Let me grep the min file.

Alternatively — maybe the problem is that `event.sourceEvent.stopPropagation()` in the "start" handler happens but zoom's listener is on the **svg**, and the event reached the svg already? No, bubble order guarantees not.

Wait — actually maybe zoom's mousedowned is registered via `selection.on("mousedown.zoom", mousedowned)` with `capture: true`? Let me check d3-zoom source:```js
function ZoomGestures(selection, filter) {
  selection.on("wheel.zoom", wheeled, {passive: false})
           .on("mousedown.zoom", mousedowned)
           .on("dblclick.zoom", dblclicked)
           ...
}
```
Non-capture. Hmm.

But wait: `svg.call(zoom)` — I called zoom on the svg element. The node `<g>` is a descendant. So mousedown on node bubbles: circle → g.node → g.root → svg. Drag handler on g.node should run first.

Let me check whether d3-drag stops propagation internally before calling handlers... Actually d3-drag's mousedowned:
```js
function mousedowned(event, that, args) {
  ...
  if (!filter.apply(that, arguments)) return;
  var view = event.view, ...
  ...
  view.on("dragstart.drag", nopropagation).on("blur.drag", dragended) ...
}
```
Hmm, `nopropagation` is registered on the *view* (window) for "dragstart.drag" — the dragstart event doesn't bubble...OK rather than guessing, let me check: is `event.sourceEvent` defined? For the synthetic drag event, `sourceEvent` is the mousedown — yes. And I call stopPropagation on it.

Hmm, but wait: in the test, did I even hover over a node correctly? before pos was (1016.8, 579.9) and after drag the camera moved by (120,80). But maybe what actually happened: the node drag worked (node moved), AND zoom panned. Let's verify whether the mouse press actually landed on the node. The node moved from 1016.8 to 1137.6 in screen coords = +120.8, +77.3 — that matches the drag delta. So the node drag worked. But the camera also moved +120,+80. So both happened. With camera moving +120,+80 and node fx/fy fixed at local coords, the node's screen pos = camera + local. If node local moved +0,+0... Actually node local position: after drag, fx/fy = event.x,event.y in the **node's parent coordinate system**? d3.drag's event.x/y are in the coordinate system of the container (default: parent node of the dragged element). The parent is g.root, which has a transform. d3-drag converts the pointer into the container's coordinate space using `pointer(event, container)` which uses getScreenCTM inverse — so event.x/y are in root's local coords = the same coords as node.x/node.y. Good.

Node moved screen +120.8,+77.3 while camera moved +120,+80 → node local moved +0.8, -2.7?? That's odd. Unless the node's local didn't change much because... hmm, actually during the drag, the camera panning shifted, and the pointer conversion compensated, so fx/fy stayed roughly at the original local position. That's consistent with both drag and pan running simultaneously.

So I need to prevent zoom's pan during node drag. Better approach: in the zoom filter, ignore mousedown events whose target is inside a `.node`. That's robust regardless of propagation. Let's do:

```js
.filter(event => {
  if (event.type === 'wheel') return !event.ctrlKey; // or just true
  if (event.type === 'mousedown' || event.type === 'touchstart') {
    const t = event.target;
    if (t && t.closest && t.closest('.node')) return false;
    return !event.ctrlKey && !event.button;
  }
  return true;
})
```

Also keep the stopPropagation. Also for touchstart.

2. **Hover doesn't highlight** — dim=0, neigh=0. The hover test moved the mouse to node 0's screen position after the camera had been changed... and I used `p.mouse.move` which should trigger mouseenter. But 0 counts everywhere. Possibly the issue: `mouseenter` listener registered via d3 `.on("mouseenter", ...)` — that works. But maybe the mouse position wasn't over the node because the camera had moved (screenPos accounts for camera, so should be right). Hmm, but after the pan/zoom the node positions may have shifted slightly due to the simulation still running (alpha decays). Actually screenPos was computed right before moving, should be accurate.

Wait — bigger issue: d3-drag on the node registers `mousedown.drag`, not mousemove capture. But d3-zoom... no. Let me think about mouseenter: playwright's mouse.move generates a mousemove; mouseenter should fire on the element under cursor. Unless the element under the cursor isn't the node because the node `<g>` bounding: circle at center, text offset to the right. Moving to the circle center should hit the circle.

Hmm, but wait — maybe `screenPos(0)` was wrong because node 0's `x/y` in data vs. actual: camera.applyX(d.x). That's the transform applied. Node group transform = translate(d.x, d.y). So circle center = camera.apply(d.x,d.y). Should be right.

Unless the simulation restarted and moved nodes between computing screenPos and the mouse move — the resize handler restarts alpha 0.35, and resetView... no reset yet at that point. Actually `resize()` is called by ResizeObserver initially, restarting the sim with alpha 0.35, so nodes drift for a while. But I waited 1s before, then did drag (which sets alphaTarget 0.22 and restarts, then alphaTarget 0 on release — after release the sim keeps going with alpha from... hmm, after drag end alphaTarget(0) means alpha decays from current value ~0.22+, so it keeps simmering for a while: alphaDecay 0.022 → time constant ~45 ticks, several seconds. So during the hover test the nodes were still moving → screenPos computed, then mouse.move immediately after; move takes a few ms; node could move a couple px. Circle radius 9-11 px, so still likely to hit.

Let me debug hover separately with fresh page and longer settle. Possibly the issue is something else: my `applyHighlight` uses `adjacency` built from links — fine. But `.classed("dimmed", n => ...)` on nodeSel — fine.

Hmm, one real possibility: **`p.mouse.move(x,y)` to node 0 position, but node 0 is at a spot where the legend overlays it!** Legend is top-right. Node 0 is one of the hubs. bounds maxY 767, minY 99. Node 0's position unknown. If it's under the legend (right side, top) or hud, the mouse would hit the legend div instead (legend has no pointer-events:none!). The legend sits at right:12px top:12px and could overlay nodes. Also the HUD at bottom-left has pointer-events: none, good, but legend doesn't.

Let me add pointer-events:none to legend (and hud already) — but legend doesn't need interaction, so pointer-events:none is safe.

Let me debug by checking elementFromPoint at the node position.

Let me write a focused debug test.

Nodes are far from the screenPos computed. The node transform is applied to `g.node` via translate(x,y) — but the elementFromPoint returns svg. Hmm, the circle should be at that point. Unless the coordinates are wrong because screenPos uses camera.applyX on d.x — but the root also may have a scale. That's fine at k=1.

Wait, node 33's y is 56 — that's inside the header area (header is at top with height ~ 50). Node positions are in stage coordinates, but screenPos returns page coordinates without adding stage offset! The svg is inside #stage which is below the header. So screen coords need stage.getBoundingClientRect().offset. That's a testing bug, not app bug. But also node 0 at x736 y 472 within stage → page y = 472 + headerHeight(~50) = 522. elementFromPoint at 472 in page coords pointed to svg (inside stage) but maybe at a spot between nodes. So my hover test used wrong coordinates too.

Also the drag test: node 5's page pos should be offset. It dragged from the wrong point but mouse.down at a background point... Actually the drag moved the camera (pan) because the mouse press started on the background — exactly the reported "cam: translate(120,80)". That's why the camera moved. So the drag test was invalid.

Fix test coordinates by adding stage offset. Also add a helper in __graph that returns page coordinates? Better: use getBoundingClientRect of the svg. Let me fix the test.

Also consider adding pointer-events: the legend/hud overlay; elementFromPoint hit svg so fine there.

Let me rerun the test with corrected page coords.

Everything works now. Camera stays fixed during node drag (translate(0,0) scale(1)). Pan works, zoom works, hover works (node 0 has 3 neighbors + itself = 4 non-dimmed; 4 active links; 40 dimmed links), leave restores. Reset returns to identity, data preserved.

Earlier the "camera moved during drag" was because in the first test I was using screen positions computed before the layout settled / offset issue — the mouse actually grabbed the background. Wait — in the first test, the drag at node 5's reported pos moved the camera by (120,80), which equals exactly the drag delta. That was because screenPos was offset by the header (~64px?) causing misses. In the corrected test it works.

One thing: link5 target moved by 17.87 — that's because the simulation continues moving. The requirement is that connected links follow the dragged node. During the drag (mid), let's verify the link end followed. Let me do a more precise check: while dragging, capture link data and node position.

Also let me check that the link start stayed attached to node 5 during drag (it should, since links read source.x/source.y).

Let me do one more precise test of "links follow the dragged node while camera stays in place": during drag, hold the pointer at a position and check the link endpoint is within ~0 of node position.

Also verify screenshot visually. Let's take a screenshot and view it.

Links stay glued to the node (gap 0), camera fixed, and after release fx/fy are cleared so simulation settles.

Now check the visual screenshot.

One consideration: the initial graph. After220 pre-ticks plus a resize-driven restart with alpha 0.35, the graph settles centered. The bounds check showed nodes spanning 174–1058 x, 98–768 y within a 1200×800 viewport (header takes ~55px, so the stage is ~745px tall; node maxY 768 page = ~713 in stage, fine). All in view. Good.

Let me look at the screenshots to confirm the visual.

The graph looks good. Four rings, hub ring linking 0-10-20-30, all in view. Let me check the hover screenshot.

Hover works: node 15 highlighted, neighbors 14 & 16 highlighted yellow, links active yellow, rest dimmed. 

One small issue: the HUD at bottom-left overlaps the graph area and has pointer-events: none, so that's fine. The legend overlaps nodes too but pointer-events default on legend — the legend is at top-right; it may block hover on nodes beneath it. Minor. I could add pointer-events:none to the legend and hud so nodes underneath stay interactive. Let me do that for robustness (legend/hud aren't interactive).

Also note the drag test worked but earlier failure was due to my test using wrong coords (header offset), not the app.

Let me add pointer-events:none to legend (hud already has it).

Also, verify zoom in/out works — yes. Reset returns to translate(0,0) scale(1) — yes, matching initial framing.

One more: initial camera framing is identity; but resize() is called on load which sets alpha to 0.35 restart — that continues simulation moving. That's fine since layout settles. But "keep the initial graph within view" — the bounds show all within1200x800. Good.

Add pointer-events:none to legend. Also verify that wheel zoom with cursor-at-600,400 keeps things centered — it did (zoom around cursor).

Then final recheck quickly.

Wait — the legend has pointer-events: none, which is fine. But hold on, the earlier hover test worked even without it. Also the earlier problem: node 33 was at y=56 in page coords which is in the header region — meaning some nodes may be hidden behind the header? No — nodes' y coordinates are relative to the SVG stage, which starts below the header. screenPos returns SVG-local coords. Bounds check showed minY ~98 in page coords, maxY ~768, so all nodes are in the stage viewport (stage is from y~56 to 800). Good.

Let me rerun the final check quickly to make sure nothing broke and confirm the full test suite passes.

All good. Clean up temp test files (they're in /tmp, not cwd, so fine). Final file exists.