feat(handles): carry the swell through the corners, and spread it

The swell was squeezed into the edge bars, between two corner pieces held
flat at band_min. Two things followed, both wrong for a moulding: the ramp
was steep, because it had only the bar's length to climb, and the corners
were visibly a different, constant thickness rather than part of the curve.

The thickness is now one profile per side — band_min at the very corner
easing to band at the midpoint — computed independently of where the ring is
cut into zones. So the corner pieces ride the same swell, and spreading the
ease over the full half-side rather than the bar alone is what makes it
gradual. smoothstep flattens the curve at both ends, leaving no crease where
the halves meet at the midpoint and none where it starts at the corner.

`corner_length` now only places the gaps and the zone boundaries; it no
longer bounds the swell.

Measured across a side, window 839px wide: 11px at 5% in, then 13, 15, 18,
24, 29, 31 at the middle, symmetric back down.

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

 CLAUDE.md                                     |  7 +++--
 scenefx/render/fx_renderer/shaders/frame.frag | 38 ++++++++++++++-------------
 2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/CLAUDE.md b/CLAUDE.md
index 73a1338..4f6dd0a 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -322,8 +322,11 @@ where the old band sat outside them.
   to be spent on moving the way the outside band's did.
 - The ring is drawn by **one scenefx node**, `wlr_scene_frame`
   (`scenefx/render/fx_renderer/shaders/frame.frag`), not by rects. Its
-  thickness swells from `band_min` at the corners to `band` at the middle of
-  each side — a picture-frame moulding — and that profile is continuous along
+  thickness swells from `band_min` at the very corner to `band` at the middle
+  of each side — a picture-frame moulding. The profile is ONE curve per side,
+  independent of the eight-zone cut: the corner pieces ride the same swell
+  rather than holding a flat thin run, and `corner_length` places the gaps
+  without bounding the curve. That profile is continuous along
   a side, which a rect cannot express: its only shaping tool is a clipped
   region whose corner radius is a single scalar, capped by the thickness
   change (tens of px) while a side is hundreds long, so it reads as a bump
diff --git a/scenefx/render/fx_renderer/shaders/frame.frag b/scenefx/render/fx_renderer/shaders/frame.frag
index 935b7ed..6ed967e 100644
--- a/scenefx/render/fx_renderer/shaders/frame.frag
+++ b/scenefx/render/fx_renderer/shaders/frame.frag
@@ -3,9 +3,12 @@
 // of a picture frame.
 //
 // The ring is cut into eight zones — four corner pieces and four edge bars —
-// separated by `gap`. A corner piece keeps the thin `band_min` thickness for
-// `corner_len` along each of its two sides; an edge bar runs from there to
-// the side's midpoint, easing from `band_min` up to `band`.
+// separated by `gap`, but the THICKNESS is one continuous profile per side,
+// independent of that cut: `band_min` at the very corner easing to `band` at
+// the side's midpoint. The corner pieces are part of the same curve rather
+// than a flat run, so the swell reads as moulding carried right around the
+// frame instead of a bar that steps up between two constant corners.
+// `corner_len` therefore places the gaps; it no longer bounds the swell.
 //
 // Why a shader rather than rects: the swell is continuous along a side, and
 // a scene rect can only approximate it with a clipped region whose corner
@@ -88,30 +91,29 @@ void main() {
     // Distance from the nearer end of that side.
     float u = min(along, len - along);
 
-    // Thickness profile and zone.
-    float thickness;
+    // Thickness: one curve over the whole half-side, corner pieces included.
+    // Spreading it across the full run rather than only the bar is what makes
+    // the swell gradual; smoothstep flattens the curve at both ends, so it
+    // leaves no crease where the two halves meet at the midpoint and none
+    // where it starts at the corner.
+    float half_side = max(0.5 * len, 1e-3);
+    float t = clamp(u / half_side, 0.0, 1.0);
+    float thickness = mix(band_min, band, smoothstep(0.0, 1.0, t));
+
+    // The cut into zones is separate from the profile: it decides where the
+    // gaps fall and which zone the pointer is over, nothing about thickness.
     float zone;
     if (u <= corner_len) {
-        // Corner piece: thin, and constant for its whole run.
-        thickness = band_min;
         bool left = dl <= dr;
         bool top = dt <= db;
         zone = top ? (left ? ZONE_TL : ZONE_TR) : (left ? ZONE_BL : ZONE_BR);
     } else if (u <= corner_len + gap) {
         // The gap between a corner piece and its neighbouring bar.
         discard;
+    } else if (vertical) {
+        zone = (dl <= dr) ? ZONE_LEFT : ZONE_RIGHT;
     } else {
-        // Edge bar: eased from band_min at the corner end to band at the
-        // side's midpoint. smoothstep rather than a straight ramp so the
-        // join at either end has no visible crease.
-        float run = max(0.5 * len - corner_len - gap, 1e-3);
-        float v = clamp((u - corner_len - gap) / run, 0.0, 1.0);
-        thickness = mix(band_min, band, smoothstep(0.0, 1.0, v));
-        if (vertical) {
-            zone = (dl <= dr) ? ZONE_LEFT : ZONE_RIGHT;
-        } else {
-            zone = (dt <= db) ? ZONE_TOP : ZONE_BOTTOM;
-        }
+        zone = (dt <= db) ? ZONE_TOP : ZONE_BOTTOM;
     }
 
     if (depth > thickness) {