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, 14 insertions, 0 deletions

diff --git a/test/snapshots/emptycol.golden b/test/snapshots/emptycol.golden
new file mode 100644
index 00000000..bb41c028
--- /dev/null
+++ b/test/snapshots/emptycol.golden
@@ -0,0 +1,14 @@
+== snap newcol grid=100x24 cursor=53,1
+|Newcol Joincol Find Grep Help Changelog Tutor Dump NextColor Debug Exit
+|   New Tty Find Grep Joincol Delcol                  New Tty Find Grep Joincol Delcol
+|   /tmp/pardes-snap/emptycol/cwd/notes.txt Save Tt
+|     1 one
+|     2 two
+== snap filled grid=100x24 cursor=54,5
+|2:    /tmp/pardes-snap/emptycol/cwd/notes.txt Save Tt   /tmp/pardes-snap/emptycol/cwd Tty+bash Save Mod
+|3:      1 one                                          ls
+|4:      2 two                                          notes.txt
+== snap emptied grid=100x24 cursor=53,1
+|2:    /tmp/pardes-snap/emptycol/cwd/notes.txt Save Tt
+|3:      1 one
+|4:      2 two