fix: preview wells flush with the pane rect across the split

The section frames were inset 8px inside the pane (SectionContext's 4 +
pad) and the content fill another 12 inside the well, so the visible
split gap read ~24px against cce-data-editor's 12. The frames now span
the full pane width (left = cx - pad cancels the inner pad; titles stay
centered), the recess carves at the pane edge, and the content fill
spans the well like the list's fill spans its rect. Wheel hit region
follows the fill.

Co-Authored-By: Claude Fable 5 <[email protected]>

 src/preview_pane.rs | 39 ++++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/src/preview_pane.rs b/src/preview_pane.rs
index cf751b0..8ec002f 100644
--- a/src/preview_pane.rs
+++ b/src/preview_pane.rs
@@ -116,10 +116,11 @@ impl PreviewPane {
     /// never reaches the widgets beneath it.
     pub fn wheel(&mut self, delta: &MouseScrollDelta, mx: f32, my: f32) -> Option<bool> {
         let (prev_x, prev_y, prev_w, prev_h) = self.rect;
-        // Inner content-preview region (below the metadata header).
-        let px = prev_x + 12.0;
+        // Inner content-preview region (below the metadata header); the fill
+        // spans the full pane width, so the hit region does too.
+        let px = prev_x;
         let py = prev_y + 32.0;
-        let pw = prev_w - 24.0;
+        let pw = prev_w;
         let ph = prev_h * 0.5 - 40.0;
         if mx < px || mx > px + pw || my < py || my > py + ph {
             return None;
@@ -208,9 +209,12 @@ impl PreviewPane {
         let relief = cce_ui::layout::control_relief();
         let radius = cce_ui::layout::list_corner_radius();
 
-        // 1. Top pane: File Preview Section
+        // 1. Top pane: File Preview Section. The section frame spans the FULL
+        // pane rect (left = cx - pad cancels SectionContext's inner pad), so
+        // the well edge sits at the pane edge like the list across the split —
+        // the visible split gap is exactly backplate_gap on both sides.
         {
-            let mut preview_sec = SectionContext::new(pc, cx + 4.0, cy + 12.0, cw - 8.0, "Preview", false, false);
+            let mut preview_sec = SectionContext::new(pc, cx - pad, cy + 12.0, cw + 2.0 * pad, "Preview", false, false);
             preview_sec.content_y = cy + half_h - pad - 12.0;
             if !relief {
                 preview_sec.finish();
@@ -218,19 +222,22 @@ impl PreviewPane {
         }
         if relief {
             let fy = cy + 12.0 + 7.0;
-            pc.relief_recessed(cx + 4.0 + pad, fy, cw - 8.0 - 2.0 * pad, (cy + half_h) - fy, radius);
+            pc.relief_recessed(cx, fy, cw, (cy + half_h) - fy, radius);
         }
         let rect_y = cy + pad + 31.0;
         let rect_h = half_h - 2.0 * pad - 43.0;
 
+        // Content fill spans the FULL well width (like the list's fill spans
+        // its rect) — the recess carves over it, so the well reads as one dark
+        // surface flush with the pane edge across the split.
         let bg_color = cce_ui::color::list_bg_color();
-        pc.rect(bg_color, cx + 12.0, rect_y, cw - 24.0, rect_h);
+        pc.rect(bg_color, cx, rect_y, cw, rect_h);
 
         if let Some((id, img_w, img_h)) = self.image_tex {
             let fitted = fit_rect(
                 img_w,
                 img_h,
-                Rect { x: cx + 12.0, y: rect_y, width: cw - 24.0, height: rect_h },
+                Rect { x: cx, y: rect_y, width: cw, height: rect_h },
                 FitMode::Contain { max_upscale: 4.0 },
             );
             pc.image(id, fitted.x, fitted.y, fitted.width, fitted.height, 1.0);
@@ -243,13 +250,13 @@ impl PreviewPane {
                 // Chars-per-width from one measured glyph (cached) instead of
                 // the old magic 6.8 px/char guess.
                 let char_w = measure_text_width("M", "monospace", 11.0).max(1.0);
-                let limit = (((cw - 40.0) / char_w).floor() as usize).max(20);
+                let limit = (((cw - 24.0) / char_w).floor() as usize).max(20);
                 let line_truncated = truncate_tail(line, limit);
-                pc.text_with_font(&line_truncated, cx + 20.0, text_y, 11.0, text_fg, "monospace");
+                pc.text_with_font(&line_truncated, cx + 12.0, text_y, 11.0, text_fg, "monospace");
                 text_y += 15.0;
             }
         } else {
-            pc.text("No preview available", cx + 20.0, rect_y + 12.0, 11.0, text_dim);
+            pc.text("No preview available", cx + 12.0, rect_y + 12.0, 11.0, text_dim);
         }
 
         // 2. Bottom pane: Details Section
@@ -271,7 +278,7 @@ impl PreviewPane {
         }
 
         {
-            let mut details_sec = SectionContext::new(pc, cx + 4.0, bottom_y, cw - 8.0, "Details", false, false);
+            let mut details_sec = SectionContext::new(pc, cx - pad, bottom_y, cw + 2.0 * pad, "Details", false, false);
             details_sec.content_y = details_content_end_y;
             if !relief {
                 details_sec.finish();
@@ -279,13 +286,7 @@ impl PreviewPane {
         }
         if relief {
             let fy = bottom_y + 7.0;
-            pc.relief_recessed(
-                cx + 4.0 + pad,
-                fy,
-                cw - 8.0 - 2.0 * pad,
-                (details_content_end_y + pad + 12.0) - fy,
-                radius,
-            );
+            pc.relief_recessed(cx, fy, cw, (details_content_end_y + pad + 12.0) - fy, radius);
         }
 
         let header_y = details_content_start_y + 6.0;