Reading this maze
Grand gallery starts at row 3, column 5. Of the 42 grid positions, 29 are paintable and 13 are walls. The start is already painted; the other 28 tiles remain to be reached.
The switch at row 3, column 4 toggles gate A on every entry. Start up; opening the gate changes where later slides can stop. The first slide covers 2 of 29 target tiles; 27 remain. Both diamonds control the same gate; visiting either flips its state, so plan the return crossing.
The verified opening crosses 1 tiles before stopping. A breadth-first search proves a 28-slide finish from this exact starting board; that is a reference target, not a move limit. You may revisit any painted tile.
Switch A is a diamond; gate A has bars when closed and a dashed outline when open. Entering the switch toggles it immediately, including during a slide. If you get trapped, undo or restart; Hint checks the current gate and painted-floor state.