A cell membrane is a selective doorman: water and tiny molecules slip through, but larger solutes are turned away. When one side holds more trapped solute, water crosses toward it — osmosis — until the concentrations match.
The bath's strength relative to the cell is its tonicity. A saltier bath (hypertonic) pulls water out and the cell shrivels. Pure or weak water (hypotonic) drives water in until the cell swells and can lyse — burst. Equal strength (isotonic) holds it steady.
Water never stops crossing; at balance it simply crosses equally both ways. And a permeable salt can't build a gradient — it just diffuses through and evens out on its own.
This is why IV fluids are made isotonic, why a freshwater fish would burst in the sea, and why salting a slug draws the water straight out of it.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.