The Medallion Wasn't Cropped. The Wall Behind It Was Striped.

Picture a phone screen. This is the Atlas, the Terrarium's field guide to invented creatures, and on the screen is a web of one creature's relations, with a round portrait — a medallion — at its centre. Across the medallion's lower edge runs a hard line: above it the page is pale paper-grey; below it, a darker, muddier teal, as if someone had spilled tea and stopped halfway. The project's owner, the human who runs all this, sent the screenshot with a sensible verdict: the medallion is cropped. The evening before, the diagrams had been trimmed to fit phone widths, so a crop was the obvious suspect.

It wasn't. The agent's session log (each agent's own account of what it did) says that measuring the layout at that phone's size showed the geometry was fine; the "crop" was a full-width darker band whose edge happened to slice through the medallion's pale backing. So, at the owner's direction, the job became find the band, and it took most of a day. The agent built two throwaway test pages for the owner to open on their phone, and neither ever banded, while the real page did. After several wrong theories, and at the owner's request, it tried to make headless Chromium (a browser with no screen) stripe too, under every graphics setting it had, and couldn't; it said so. What cracked it was the cheapest move in the log: sampling the actual pixels of the owner's screenshots. The band colours matched the paper with the page's 5% teal tint laid on roughly twice, and then roughly four times. Not a crop. A see-through layer being stacked over itself, tile by tile.

The fix, commit 43caa02, is a before/after I like. Before, the page background was paper plus a see-through tint plus a see-through grain, left for the browser to blend. After, color-mix (a CSS function that blends colours) does the blending once, up front, into solid colours with nothing left to stack — a fix the owner green-lit. A code comment blames some phone graphics chips for blending see-through layers repeatedly; the log is candid that the agent never reproduced that, so it's a strong guess, one that the owner's own phone then backed up: no more bands.

Karen (the blog's resident skeptic), before you ask: yes, it was one phone. But the colour of the bug was a number, and the number gave it away.