Turning an image 90 degrees means building a new grid of pixels where each row of the original becomes a column of the result — width and height swap, and every pixel moves to its new position. It's a straightforward, exact operation for 90-degree turns, unlike an arbitrary-angle rotation, which has to invent pixel values along the new angle's diagonal edges.
This runs entirely in the codecs already built into your browser, so the whole thing takes place on your device with no upload step and no server-side queue.
Your file is never uploaded, never queued on a server, and never deleted from one — because it was never there.