Skybox image: fix HDR sky binding; clip checkbox/arrow drawing

The HDR sky materials use the "sky" shader with $hdrcompressedtexture (DXT5).
Assigning an RGBA8 procedural texture there sampled as compressed data and
rendered black. Point $hdrbasetexture at the image, undefine
$hdrcompressedtexture (and its 0/1/2 variants) so the shader falls back, and
call IMaterial::Refresh (37) because the sky shader binds textures in
SHADER_INIT, which is otherwise cached.

GUI: draw_checkbox and the card expand chevron ignored the content clip, so
cards scrolled out of view leaked header widgets outside the window.

Log the first regenerator call (size/pitch/first pixel) for diagnosis.

1 files changed, 13 insertions, 3 deletions

diff --git a/CONTEXT.md b/CONTEXT.md
index 5bd0436..b07e407 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -144,6 +144,10 @@ vocabulary / decisions.
   `x`, `y`, `category` and an `expanded` bitmask (card index order). Every
   feature now persists an `active` and `bind` pair, including movement, melee
   and spread.
+- All card contents are clipped to the scrolling content rect, including
+  checkboxes and the expand chevron; only clipped fills/text were handled
+  before, so cards scrolled out of view leaked header widgets outside the
+  window.
 - **Colour control (`CK_COLOR`)**: row shows a live swatch; clicking the row
   expands an inline picker (saturation/value square + hue bar + hex/RGB
   preview) instead of three RGB sliders, growing the card in place so it
@@ -377,9 +381,15 @@ vocabulary / decisions.
   `IVTFTexture::ImageData(frame,face,mip)` (39). `IVTFTexture`'s virtual
   destructor occupies two slots, so Width=15, Height=16, RowSizeInBytes=19.
 - The texture is assigned with `IMaterialVar::SetTextureValue` to
-  `$basetexture`, plus `$hdrbasetexture` / `$hdrcompressedtexture` when those
-  vars exist, on every material in the `SkyBox textures` group or named
-  `skybox/*`. The same image is mapped onto all six faces.
+  `$basetexture` and `$hdrbasetexture` on every material in the `SkyBox
+  textures` group or named `skybox/*`. The same image maps onto all six faces.
+- HDR sky materials use the `sky` shader, whose texture binding happens in
+  `SHADER_INIT`: it samples `$hdrcompressedtexture` (DXT5) when defined and
+  otherwise `$hdrbasetexture`. Putting an RGBA8 texture into the DXT5 slot
+  renders black, so `$hdrcompressedtexture` (+ its `0/1/2` variants) is
+  `SetUndefined()` and `$hdrbasetexture` is pointed at our texture instead.
+  The shader state is then rebuilt with `IMaterial::Refresh()` (slot 37),
+  otherwise the old bindings stay cached.
 - Original textures are recorded per material/var (texture pointer plus the
   string as a fallback) and restored when the feature is disabled. Records
   survive level changes so a reused sky material can still be restored; the