Агар-агар (Agar-agar)

hackerlab

Task: a deployed fork of huytd/agar.io-clone hides the flag as stego in a served static asset, teased by a hint about writing dots a special way since school. Solution: diff all served assets against the upstream repo via SHA-256 to isolate a modified css/main.css whose added comment stores ~86 (x,y) coordinate pairs; plotting them in order on a grid spells the phrase wrapped in CODEBY{}.