Replace a stillborn placeholder pane when a pane joins its column, and focus the pane a directional Del grows

A pane that joins a column whose only other pane is an untouched empty
scratch (Newcol's, or the stand-in a closed column leaves) takes the column
whole. Checked at the end of the step, since the pane that asked for the
joiner is often the placeholder itself.

Del k|j focuses the pane that took the rows.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index a5dbf6cd..ac336ce0 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -517,7 +517,9 @@ pub const Del = struct {
             if (c.pane.msg_announcement) c.pane.msg_len = 0;
             return;
         }
-        c.p.removePane(c.id, to) catch |err| c.p.reportError(c.id, "close", err);
+        c.p.removePane(c.id, to) catch |err| return c.p.reportError(c.id, "close", err);
+        // Del k|j is a direction: focus lands where the rows went.
+        if (to) |gainer| c.p.active = gainer;
     }
 };