Flagbreaker Mine Grid Puzzle

Builds a complete numbered-grid mine-flagging puzzle game (configurable grid/mine count, first-click-safe, flood-fill cascade). Found and fixed two real bugs via targeted unit testing: a fixed-grid-size bounds bug, and a flood-fill cascade that could silently reveal a flagged cell. 36 unit tests plus 45 fully-automated random games through the real UI, 0 errors, flag protection holds under real play. (AI-assisted, hand-verified.)