fix(render): preserve transparency inheritance

Resolve ByBlock alpha independently from color and keep explicit opaque values from falling back to layer transparency.

Pin the matching cadcodec API across desktop, plugin, and web targets.

Refs HakanSeven12/cadcodec#2

src/scene/view/render.rs

@@ -2863,7 +2863,7 @@ pub(crate) fn render_style_for_viewport(
             _ => 0,
         };
         let [r, g, b, _] = tess_util::aci_to_rgba(resolved);
-        let transparency = if common.transparency.alpha() == 0 {
+        let transparency = if common.transparency.is_by_layer() {
             viewport_override(
                 document,
                 layer_name,
@@ -3077,18 +3077,21 @@ pub(crate) fn render_style_for_block_sub_viewport(
     let on_l0 = is_effective_layer_zero(&common.layer);
 
     let has_book_color = has_resolved_book_color(document, e);
-    let final_color = if !has_book_color && common.color == AcadColor::ByBlock {
+    let resolved_rgb = if !has_book_color && common.color == AcadColor::ByBlock {
         insert_color
     } else if !has_book_color && on_l0 && common.color == AcadColor::ByLayer {
-        let alpha = if common.transparency.alpha() == 0 {
-            l0.color[3]
-        } else {
-            color[3]
-        };
-        [l0.color[0], l0.color[1], l0.color[2], alpha]
+        l0.color
     } else {
         color
     };
+    let alpha = if common.transparency.is_by_block() {
+        insert_color[3]
+    } else if on_l0 && common.transparency.is_by_layer() {
+        l0.color[3]
+    } else {
+        color[3]
+    };
+    let final_color = [resolved_rgb[0], resolved_rgb[1], resolved_rgb[2], alpha];
 
     let lt_bylayer =
         common.linetype.is_empty() || common.linetype.eq_ignore_ascii_case("bylayer");
@@ -4319,4 +4322,22 @@ mod layer0_inherit_tests {
         assert_eq!(&c[..3], &walls[..3], "RGB inherited from the insert layer");
         assert!((c[3] - 0.5).abs() < 0.02, "child's own 50% transparency is kept, got {}", c[3]);
     }
+
+    #[test]
+    fn byblock_transparency_inherits_insert_alpha() {
+        let d = doc();
+        let mut entity = child("Other", Color::Index(3));
+        entity.common_mut().transparency = Transparency::BY_BLOCK;
+        let color = resolve(&d, &entity, [0.2, 0.4, 0.6, 0.25]);
+        assert_eq!(color[3], 0.25);
+    }
+
+    #[test]
+    fn explicit_opaque_does_not_inherit_alpha() {
+        let d = doc();
+        let mut entity = child("0", Color::ByLayer);
+        entity.common_mut().transparency = Transparency::OPAQUE;
+        let color = resolve(&d, &entity, [0.2, 0.4, 0.6, 0.25]);
+        assert_eq!(color[3], 1.0);
+    }
 }