explore panics in debug mode

Describe the bug

explore panics when scrolled past the end

How to reproduce

1. run $env | explore
2. Keep using PageDown till it stops scrolling
3. Pres the down arrow

Expected behavior

Do nothing (already viewing the end of table)

Screenshots

 × Main thread panicked.
  ├─▶ at crates/nu-explore/src/views/record/mod.rs:697:5
  ╰─▶ 77 76
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.

This is on

fn get_percentage(value: usize, max: usize) -> usize {
    debug_assert!(value <= max, "{value:?} {max:?}");

Configuration

Additional context

The problem seems to be WindowCursor manages both "view" and a "window" that sometimes seems to be assumed to fit within the view. But sometimes it isn't clamped on update and this seems to trigger the debug_assert.

I was looking at fixing, but realized the current design is a bit unhandy:

• WindowCursor has view and window fields
  • But the view field really defines the view size and window position
  • While the window field defines the window size and cursor position within the window
  • So if you want to move the window, you update the view field!
• We need to maintain the invariant that the window always fits within the view (so that the cursor can't move past data)
  • With the current design it's lossy - you can keep clamping the window due to operations on WindowCursor, but you lose the original size and so can't reliably "unclamp" it on reverse operations
  • In practice it kind of works because the drawing code happens to reset window sizes - but it still feels unnatural it's needed, could lead to issues in the future and might already be a problem (if the reset happens too early/too late); not sure
  • Alternatively, we could "merge" Cursor into WindowCursor so that we can preserve the window size information (while reporting the clamped value via the public API). With Cursor being a separate thing, many methods don't have enough information to do that.

Any thoughts about getting rid of Cursor as a separate entity so that we can preserve the original window size?

Reproduce the debug-mode panic with $env | explore, paging past the end and pressing the down arrow. Inspect crates/nu-explore/src/views/record/mod.rs around get_percentage and the WindowCursor/Cursor behavior described in the report. Done means reaching the end of the table and pressing down no longer triggers the debug assertion.