The loop runs.
On a real repo. In your terminal.

{
  "sessionId": "jam-sess-2014",
  "vendor": "jam",
  "url": "http://localhost:5173/",
  "browser": { "name": "chrome", "version": "125.0.0.0", "os": "macOS 14.4" },
  "events": [
    { "seq": 0, "type": "nav", "url": "http://localhost:5173/", "ts": 0 },
    { "seq": 1, "type": "state-snapshot", "path": "segments[0].x", "value": 0 },
    { "seq": 2, "type": "state-snapshot", "path": "segments[1].x", "value": 200 },
    { "seq": 3, "type": "state-snapshot", "path": "segments.length", "value": 2 },
    /* …42 more events: pointerdown / pointermove×N / pointerup / final state-snapshot… */
    { "seq": 45, "type": "pointer", "phase": "up",   "targetName": "seg-0", "x": 240, "y": 32, "pointerId": 1 },
    { "seq": 46, "type": "state-snapshot", "path": "segments[0].x", "value": 0 }
  ]
}

import { describe, expect, test } from 'vitest';
import {
  dispatchDrag,
  getStateSnapshot,
  setClock,
} from '@cuit/harness';

describe('issue-2014 — segment 0 drag must not collide-noop', () => {
  test('drags segment 0 right by 100px and asserts state moves', () => {
    setClock(1716800000000);

    dispatchDrag('seg-0', 100, 0);

    const snapshot = getStateSnapshot();
    expect(snapshot['segments[0].x']).toEqual(100);
  });
});

// packages/demo-app/src/App.tsx — bug version

// Inside the pointermove handler:
setSegments((prev) => {
  const next = prev.map((s) => ({ ...s }));
  const moving = next[idx];
  const proposedX = drag.originX + dx;

  // BUG: the collision check is too eager — it blocks
  // every move that would even momentarily overlap.
  const collides = next.some((other, j) => {
    if (j === idx) return false;
    return proposedX < other.x + other.width &&
           other.x < proposedX + moving.width;
  });
  if (collides) return prev;          // <-- silently no-op'd

  moving.x = proposedX;
  return next;
});

// packages/demo-app/src/App.tsx — fix version

// Inside the pointermove handler:
setSegments((prev) => {
  const next = prev.map((s) => ({ ...s }));
  const moving = next[idx];
  const proposedX = drag.originX + dx;

  // FIX: drop the over-eager collision short-circuit.
  // Free positioning; downstream layout handles overlap.

  moving.x = proposedX;
  return next;
});