A column can be empty, as acme's can; new panes go where acme's makenewwindow puts them

Newcol makes an empty column; closing a column's last pane leaves it empty with
the keyboard on its tag; Delcol and Joincol alone take a column away; the
session's last pane closing quits. The +New stand-in and replaceStillborn /
stillborn_joiner are gone. Every new pane goes through exec.placeNew, which
follows acme's makenewwindow (active column, empty column whole, blank space,
halving the biggest) or, with Placement pardes, the old rules. ColumnTags is
gone: column tags are always shown. A grip drag shows acme's box cursor.

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

1 files changed, 22 insertions, 0 deletions

diff --git a/test/snapshots/emptycol.snap b/test/snapshots/emptycol.snap
new file mode 100644
index 00000000..edf61eed
--- /dev/null
+++ b/test/snapshots/emptycol.snap
@@ -0,0 +1,22 @@
+# A column can hold no pane, as acme's can (cols.c:186). Newcol makes one
+# empty, its tag over blank space and holding the keyboard; the next pane
+# made while it is the active column fills it whole (makenewwindow,
+# util.c:468-469); and a shell that exits there leaves it empty again, the
+# keyboard back on its tag.
+file notes.txt one\ntwo
+config Verbose off
+start 24 100 notes.txt
+wait 8000 notes.txt
+stable 700 20000
+key space c n
+stable 400 5000
+snap newcol
+key a-n
+stable 700 15000
+snap filled
+key c-b
+stable 400 5000
+text exit
+key enter
+stable 700 10000
+snap emptied