pub const MAX_HEADER_SIDEBAR_ACTIONS: usize = 2;Expand description
The header strip is shared with the window controls, so it holds a few actions rather than an open-ended list. Exceeding it rejects the whole declaration instead of truncating: silently dropping one entry would leave an app believing it published something the user cannot see.
The header is a borrowed corner of the window’s caption row, shared with the traffic lights or app menu and the collapse toggle. Two icon-only buttons is what reads as a pair a person can learn; past that it becomes a row of unlabelled glyphs in the part of the window that belongs to the window.
Exceeding it rejects the whole declaration instead of truncating: silently dropping one would leave an app believing it published something the user cannot see. Anything that must always be reachable belongs in the footer, which is unbounded and scrolls.