Issues with reordering system markings in panel

[avvvvve]

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

Found in this PR which will likely be merged tomorrow.

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Adjacent system markings

In the Layout panel, if you drag a system marking next to another one, it seemingly disappears from the list, but this causes other issues.

1. The text displayed in the system marking row changes
   • In the first video (0:00-0:20), I drag a 'Time signature, system text & rehearsal mark' row next to another one, and one disappears but the remaining row just says 'Time signature'. When the options are opened, each system marking type still looks visible, but clicking the eye icons doesn't do anything.
   • In the second video, making system markings adjacent causes the row to say just 'System markings' (the empty state) and the eye appears off.
2. Dragging a system marking row next to the topmost system marking does the same as above, but additionally can cause certain elements to appear twice above the system (i.e. the two rehearsal marks shown after 0:20 in the first video)

system-marking-dupes.mov

system-marking-draghide.mov

Expected behavior: We should not allow two system marking rows to be next to each other in the Layout list

MVP solution: If you move a system marking next to another one, just delete one of them.

Better solution: Instead of deleting one of the system markings...

• If I've dropped it below a system marking/above an instrument, move it to the next available slot between two instruments beneath where it was dropped
• If I've dropped it below an instrument/above a system marking, move it to the next available slot between two instruments above where it was dropped
• Same goes for if I reorder system markings with the arrows—they should jump to the next slot between two instruments. If there is no such slot below, disable the 'Down' arrow next to the 'Add' button (and disable 'Up' if no slot is above).

Adding new system markings should follow similar logic.

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System markings should not be at the end of the list

It's not possible to drag a system marking beneath the last instrument in the Layout list (expected), but you can still get it there by:

• using the arrows in the panel to move it down
• using the arrows in the panel to move the last instrument up

Screen.Recording.2025-02-19.at.4.07.15.PM.mov

Expected behavior:

• If a system marking is above the last instrument in the list, disable the 'Down' arrow at the top of the panel while it's selected.
• If I press the up arrow on the last instrument in the list, copy the same behavior that happens when you try to drag it above the system object (the second to last instrument moves down, and the system object stays above it)

Screen.Recording.2025-02-19.at.4.08.08.PM.mov

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Reaching the maximum number of system markings

Edge case

If there are no available slots in the list left between two instruments, the Layout > Add > 'System markings...' option should be disabled

When this happens...

...disable this.

Supporting files, videos and screenshots

See above

What is the latest version of MuseScore Studio where this issue is present?

#26588

Regression

No.

Operating system

macOS 15

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible