Panes: one uniform gutter, from the DE's own spacing

Every inset around the panes was a different private literal — 10 at the
sides, 15 under the bar and at the bottom, 20 between them. Take them all
from the two DE-wide values instead: root_plate_padding for the frame
(rim to content, 12 here) and root_plate_gap for the split, whose own doc
names pane splits as its case. Left, right, top, bottom and the gap
between the panes are now the same number, and follow the config.

LIST_X, LIST_SEP_GAP, LIST_DETAIL_GAP, LIST_BOTTOM_PAD, SEARCH_ROW_Y and
LIST_TOP_WITH_SEARCH are gone with them; the search band's own spacing
derives from the same pair rather than a 55 that had to be recomputed by
hand whenever anything above it moved. The drag clamp follows the grab
band to the gap's centre line.

DETAIL_PAD stays: padding INSIDE a pane is not padding around one.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

 src/main.rs | 78 ++++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 49 insertions(+), 29 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 34a3c6a..f0a8199 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -594,18 +594,30 @@ const MENUBAR_H: f32 = 36.0;
 const MAIL_BUTTON_PX: f32 = 26.0;
 const MAIL_BUTTON_X: f32 = 8.0;
 
-// List/detail split geometry. The list band starts at LIST_X; the separator
-// line sits LIST_SEP_GAP after the band and the detail pane LIST_DETAIL_GAP
-// after the separator. `list_w` (the band width) is the one draggable value —
-// everything else derives from it through `split_geom`.
-const LIST_X: f32 = 10.0;
-const LIST_SEP_GAP: f32 = 10.0;
-/// How far the detail pane's content sits inside its plate. Also the gap
-/// from the separator line to the plate's left edge, which is LIST_SEP_GAP
-/// so the line is centred between the two plates rather than hugging one.
+// List/detail split geometry. `list_w` (the list plate's width) is the one
+// draggable value — everything else derives from it through `split_geom`,
+// against the two DE-wide spacings below.
+
+/// The gutter between the window plate's rim and what sits on it
+/// (`style.surface.plate.root.padding`, DE-wide). EVERY inset around the
+/// panes is this one value — left, right, under the menubar, bottom — so the
+/// frame around them is uniform. cce-mail used to carry its own 10 for the
+/// sides and 15 for top and bottom.
+fn pane_pad() -> f32 {
+    cce_ui::layout::root_plate_padding()
+}
+
+/// The gap between sibling objects on the window plate
+/// (`style.surface.plate.root.gap`, DE-wide) — its own docs name pane splits
+/// as the case. One gap separates the two panes, with the drag band on its
+/// centre line.
+fn pane_gap() -> f32 {
+    cce_ui::layout::root_plate_gap()
+}
+
+/// How far the detail pane's content sits inside ITS plate. Padding within a
+/// pane, not around one, so it is not `pane_pad`.
 const DETAIL_PAD: f32 = 15.0;
-/// Separator line to detail CONTENT: across the gap, then the plate's padding.
-const LIST_DETAIL_GAP: f32 = LIST_SEP_GAP + DETAIL_PAD;
 const LIST_W_DEFAULT: f32 = 300.0;
 const LIST_W_MIN: f32 = 180.0;
 /// The detail pane never gets squeezed below this by a drag or a narrow window.
@@ -625,10 +637,7 @@ const CONTEXT_ROW_H: f32 = 24.0;
 // The search band. It is not permanent chrome: the `open_search` chord
 // ("/" by default) reveals and focuses it, and closing hands its strip back
 // to the list, so `list_geom` is the single source for where the rows start.
-const SEARCH_ROW_Y: f32 = 15.0;
 const SEARCH_ROW_H: f32 = 26.0;
-const LIST_TOP_WITH_SEARCH: f32 = 55.0;
-const LIST_BOTTOM_PAD: f32 = 15.0;
 
 // Detail-pane vertical layout, every offset measured from the pane plate's
 // top edge (`detail_origin_y`) — they were measured from the menubar back
@@ -2962,19 +2971,27 @@ impl ClearEmailApp {
     /// layout, and every hit-test — the stored `list_w` preference is never
     /// mutated by a window resize, only re-clamped here.
     fn split_geom(&self) -> (f32, f32, f32) {
-        let max_w = (self.width as f32 - LIST_X - LIST_SEP_GAP - LIST_DETAIL_GAP - DETAIL_W_MIN)
-            .max(LIST_W_MIN);
+        let (pad, gap) = (pane_pad(), pane_gap());
+        // What is left for the detail plate once both outer gutters and the
+        // split gap are taken: it may not fall under DETAIL_W_MIN.
+        let max_w = (self.width as f32 - 2.0 * pad - gap - DETAIL_W_MIN).max(LIST_W_MIN);
         let lw = self.list_w.clamp(LIST_W_MIN, max_w);
-        let sep = LIST_X + lw + LIST_SEP_GAP;
-        (lw, sep, sep + LIST_DETAIL_GAP)
+        // The grab band rides the gap's centre line; the detail plate starts a
+        // whole gap past the list, and its content one plate padding inside.
+        let sep = pad + lw + gap / 2.0;
+        (lw, sep, pad + lw + gap + DETAIL_PAD)
     }
 
     /// The email list's band: (top y, height). The search row above it only
     /// exists while the band is open, and the list takes that strip back when
     /// it closes — so nothing hardcodes the top.
     fn list_geom(&self) -> (f32, f32) {
-        let top = if self.search_open { LIST_TOP_WITH_SEARCH } else { SEARCH_ROW_Y } + MENUBAR_H;
-        (top, (self.height as f32 - top - LIST_BOTTOM_PAD).max(50.0))
+        let pad = pane_pad();
+        // One padding below the bar; the open search band and its own gap push
+        // the plate further down.
+        let band = if self.search_open { SEARCH_ROW_H + pane_gap() } else { 0.0 };
+        let top = MENUBAR_H + pad + band;
+        (top, (self.height as f32 - top - pad).max(50.0))
     }
 
     /// The detail pane's plate: (x, y, w, h). It shares the list's vertical
@@ -2982,10 +2999,11 @@ impl ClearEmailApp {
     /// right — two plates either side of the separator, which the equal gaps
     /// leave centred between them.
     fn detail_pane_geom(&self) -> (f32, f32, f32, f32) {
-        let (_, sep, _) = self.split_geom();
+        let (lw, _, _) = self.split_geom();
         let (top, h) = self.list_geom();
-        let x = sep + LIST_SEP_GAP;
-        let w = ((self.width as f32 - LIST_X) - x).max(DETAIL_W_MIN);
+        let pad = pane_pad();
+        let x = pad + lw + pane_gap();
+        let w = ((self.width as f32 - pad) - x).max(DETAIL_W_MIN);
         (x, top, w, h)
     }
 
@@ -3470,7 +3488,7 @@ impl ClearEmailApp {
         let w_f32 = self.width as f32;
         let h_f32 = self.height as f32;
 
-        let list_x = LIST_X;
+        let list_x = pane_pad();
         let (list_w, _separator_x, detail_x) = self.split_geom();
         // Row-label char budgets scale with the band; the bases are the
         // hand-tuned counts at the 300px default.
@@ -4555,7 +4573,7 @@ impl Application for ClearEmailApp {
 
         let current_folder_str = self.current_folder.clone();
 
-        let list_x = LIST_X;
+        let list_x = pane_pad();
         let (list_w, _separator_x, detail_x) = self.split_geom();
 
         if self.needs_rebuild || size_changed {
@@ -4611,7 +4629,7 @@ impl Application for ClearEmailApp {
             // when closed so a stale rect can't be hit by anything that still
             // routes to it.
             if self.search_open {
-                self.search_box.set_rect(list_x, SEARCH_ROW_Y + MENUBAR_H, list_w, SEARCH_ROW_H);
+                self.search_box.set_rect(list_x, MENUBAR_H + pane_pad(), list_w, SEARCH_ROW_H);
             } else {
                 self.search_box.set_rect(-9999.0, -9999.0, 0.0, 0.0);
             }
@@ -5145,9 +5163,11 @@ impl Application for ClearEmailApp {
         // neither pane collapses. Clamp into the stored value (not just at
         // paint) so the release persists what the user actually sees.
         if !self.compose_open && self.split_dragging {
-            let max_w = (self.width as f32 - LIST_X - LIST_SEP_GAP - LIST_DETAIL_GAP - DETAIL_W_MIN)
-                .max(LIST_W_MIN);
-            let new_w = (px - LIST_X - LIST_SEP_GAP).clamp(LIST_W_MIN, max_w);
+            let (pad, gap) = (pane_pad(), pane_gap());
+            let max_w = (self.width as f32 - 2.0 * pad - gap - DETAIL_W_MIN).max(LIST_W_MIN);
+            // The pointer holds the gap's centre line, which is where the grab
+            // band is — so the list ends half a gap back from it.
+            let new_w = (px - pad - gap / 2.0).clamp(LIST_W_MIN, max_w);
             if (new_w - self.list_w).abs() > 0.5 {
                 self.list_w = new_w;
                 changed = true;