Under pardes's placement a pane whose neighbour is in no column goes at a column's foot, not nowhere

After Delcol took the last column's panes, pane/new under Placement made a scratch that no column held, since a scratch was placed only under the asking pane, which was gone; a look from it then unwrapped the missing parent in belowParent and panicked (the 9P monkey's crash-e1873f34). Both now fall back to the foot of the active column, else the last.

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

1 files changed, 11 insertions, 2 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 87f6da40..2c42389c 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -1150,7 +1150,7 @@ fn pardesPlace(p: *Pardes, from: usize, id: usize, kind: NewPane) void {
         .scratch, .fs => if (layout.findPane(p, from)) |sf| {
             layout.insert(p, sf.col, sf.idx + 1, id);
             layout.splitBelow(p, from, nt);
-        },
+        } else atFoot(p, id),
         .shell => belowParent(p, from, id),
         .doc, .errors => pardesDoc(p, from, id),
         .command => {
@@ -1160,9 +1160,18 @@ fn pardesPlace(p: *Pardes, from: usize, id: usize, kind: NewPane) void {
     }
 }
 
+/// Where a pane goes when the one it would go under is in no column (Delcol
+/// took them all, or it was never placed): the foot of the active column,
+/// else of the last.
+fn atFoot(p: *Pardes, id: usize) void {
+    const c = p.activeColumn() orelse p.ncol - 1;
+    layout.insert(p, c, p.col_n[c], id);
+    if (p.col_n[c] == 1) p.panes[id].?.vweight = 1;
+}
+
 fn belowParent(p: *Pardes, from: usize, id: usize) void {
     const parent = layout.splitParent(p, from);
-    const f = layout.findPane(p, parent).?;
+    const f = layout.findPane(p, parent) orelse return atFoot(p, id);
     layout.insert(p, f.col, f.idx + 1, id);
     layout.splitBelow(p, parent, p.panes[id].?);
 }