compact: shared borders instead of gaps (D23)

One knob, `compact true`: panes pack flush against 1-cell divider lines
that meet in real junctions, one frame rings the tab, and a pane's title
rides the line above it -- a boundary costs one cell where the default
look spends four. The lines are strokes: each write says which edges of
its cell it needs, unions with what is there, and never clobbers text,
so ├ ┬ ┼ fall out of paint order and the focus ring recolours without
inventing arms. The divider *is* the gap (eff_gap, one answer for the
layout, split_fits and the resize clamp), so gap hits, hover hints and
corner drags work unchanged. Interior edges give up click-to-split --
one cell cannot hold two verbs -- and a pane's status row overlays its
last content row. Floats, zoom and the D6 flatten keep classic frames
through place_hidden: zero new tree cases.

Underneath it, mode or no mode: a border drag now moves the boundary on
that side, converted on the first motion so the press that never moves
keeps its old meaning -- the handle's click still splits, the rim's is
still deliberately nothing (drag.rim). Which is also the fix for gap 0,
where flush panes leave no gap cell to grab and the resize gesture had
silently vanished with it.

1 files changed, 7 insertions, 0 deletions

diff --git a/include/config.h b/include/config.h
index b251aed..93b1081 100644
--- a/include/config.h
+++ b/include/config.h
@@ -135,6 +135,13 @@ typedef struct {
    * and so a number means the same thing wherever it appears, however many of
    * them were written. Written as 1, 2 or 4 values, CSS order. */
   uint16_t pad_top, pad_right, pad_bottom, pad_left;
+  /* Shared borders instead of gaps: panes pack flush against 1-cell divider
+   * lines, one outer frame rings the tab, and each pane's title rides the
+   * line above it. `gap` and `gap_aspect` stop applying (the boundary *is*
+   * the divider); `padding` still does. The dividers carry the same resize
+   * drag the gaps did; interior edges give up their click-to-split — a
+   * one-cell line cannot be both verbs — and the outer frame keeps it. */
+  bool compact;
   bool rounded;
   align_t title_align;
   /* Cells between a frame's corner and the start of its title. The title