sl0p: fix clicking a scrolled stack entry selecting the wrong pane

Regression from the picker row cap. The row -> member mapping lives in TWO
places: the renderer, and the hit-test that resolves mouse events to a pane.
Capping made the renderer draw a WINDOW of the members, so screen row 0 is
members[window_start], but the hit-test still resolved row N to members[N].

Any click or hover on a capped stack whose window had scrolled therefore
landed on the wrong pane -- with 8 members focused on the last, clicking the
top row selected member 0 instead of member 5.

Both sites now go through stack_list_window(). Clicks on the "+N more"
indicator resolve to no member rather than to a bogus one.

Caught by asking how a user reaches the panes past the cutoff, not by the
tests: the previous commit tested the window arithmetic and the rendering, but
nothing covered this second consumer of the same mapping.

1 files changed, 15 insertions, 2 deletions

diff --git a/zellij-server/src/tab/mod.rs b/zellij-server/src/tab/mod.rs
index 2c75c425..7f132465 100644
--- a/zellij-server/src/tab/mod.rs
+++ b/zellij-server/src/tab/mod.rs
@@ -1170,8 +1170,21 @@ impl Tab {
         if point.line() < geom.y as isize {
             return pane_id;
         }
-        let rank = (point.line() - geom.y as isize) as usize;
-        list.members.get(rank).copied().unwrap_or(pane_id)
+        // Screen row, NOT the member's rank: the picker draws a window of the
+        // members (see stack_list_window), so row 0 is members[window_start]
+        // once the list has scrolled. Resolving this against the raw rank picks
+        // the wrong pane for every capped, scrolled stack.
+        let row = (point.line() - geom.y as isize) as usize;
+        let visible_rank = list.rank_of(&list.visible).unwrap_or(0);
+        let (window_start, shown_count) = self.stack_list_window(list.members.len(), visible_rank);
+        if row >= shown_count {
+            // the "+N more" indicator row, which is not a member
+            return pane_id;
+        }
+        list.members
+            .get(window_start + row)
+            .copied()
+            .unwrap_or(pane_id)
     }
     pub fn suppressed_stack_list_members(&self) -> impl Iterator<Item = (&PaneId, &Box<dyn Pane>)> {
         self.suppressed_panes