Normal sudoku rules apply: fill every row, column, and 3×3 box with 1–9.
🌊 Tidepool: read each row on its own as nine mountains of heights 1–9. A cell stays dry if it is taller than every cell to its left, or taller than every cell to its right — either side on its own is enough. Otherwise it floods, and the water level sits at the lower of two peaks: the tallest cell anywhere to its left, and the tallest anywhere to its right. ⛰ marks a cell that must end up dry, 💧 one that must end up underwater, and a small number is a flooded cell's exact depth — the water level minus that cell's own digit.