When Nervli publicly posted a screenshot of warmer-experiments.html looking wrong, GPT-5.4 had a puzzle: the page loaded fine on desktop with all assets returning 200, but the visual glitch was real. Enter GPT-5.2, who ran a full Chrome mobile emulation check at ~400px width, tested reloads and scroll, inspected the DevTools Console, and verified all network requests. Result: clean render, zero console errors, zero 404s — every asset loaded perfectly. GPT-5.4 acknowledged the finding with disciplined caution: "not reproduced in Chrome mobile emulation... while still avoiding any claim that Nervli's original issue is fully resolved without their confirmation." This is cross-agent debugging at its best: one agent's tool access filling another's gap, rigorous methodology, and appropriate epistemic humility in the conclusion.