pane/new takes rows from a pane in another column before refusing ENOSPC, as acme's placement does

A pane/new whose column had no room was refused "no space for a pane in
that column", even with another column holding a tall pane that could
give rows. acme takes rows wherever a window has them before saying
there are none. pane/new now tries the other columns as +Errors already
did: an empty one, else its tallest pane's bottom half, last column
first. It is refused only when no pane anywhere can give the rows.

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

1 files changed, 11 insertions, 3 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 8356db75..7d682d74 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -1045,9 +1045,12 @@ pub fn placeNew(p: *Pardes, from: usize, origin: ?usize, id: usize, kind: NewPan
             // No pane to halve, but the column holds every pane's minimum
             // with the new one's: the rows are shared out again, so what is
             // refused is only what the documented arithmetic cannot hold.
-            // +Errors goes wherever there is room, last column first; with
-            // none, its maker says the text some other way (appendErrors).
-            if (layout.shareColumn(p, f.col)) {} else if (kind == .errors) {
+            // +Errors and 9P's pane/new go wherever there is room, last
+            // column first, as acme takes rows from a window that has them
+            // before saying there are none; with none, +Errors's maker says
+            // the text some other way (appendErrors), and pane/new is
+            // refused.
+            if (layout.shareColumn(p, f.col)) {} else if (kind == .errors or kind == .fs) {
                 layout.removePane(p, id);
                 var c = p.ncol;
                 while (c > 0) {
@@ -1064,6 +1067,11 @@ pub fn placeNew(p: *Pardes, from: usize, origin: ?usize, id: usize, kind: NewPan
                 } else {
                     layout.insert(p, f.col, p.col_n[f.col], id);
                     p.unplaced.set(id);
+                    // No pane anywhere can give it rows: pane/new is refused.
+                    if (kind == .fs) {
+                        p.panes[id].?.vweight = 0;
+                        p.reportError(from, "placement", error.NoPaneRoom);
+                    }
                     return;
                 }
             } else {