refactor: move common/shaders/ to src/shaders/

Relocates shared WGSL shaders under src/ where all source code lives,
eliminating the top-level common/ directory.

- Update asset references in workspaces/main/assets.txt and workspaces/test/assets.txt
- Update docs: PROJECT_CONTEXT.md, ARCHITECTURE.md, WORKSPACE_SYSTEM.md, SHADER_REUSE_INVESTIGATION.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/src/shaders/math/common_utils.wgsl b/src/shaders/math/common_utils.wgsl
new file mode 100644
index 0000000..6ebc25a
--- /dev/null
+++ b/src/shaders/math/common_utils.wgsl
@@ -0,0 +1,46 @@
+// Common utility functions for WGSL shaders.
+// Reduces duplication across renderer_3d, mesh_render, etc.
+
+// Constants
+const PI: f32 = 3.14159265359;
+const TAU: f32 = 6.28318530718;
+
+// Transform normal from local to world space using inverse model matrix
+fn transform_normal(inv_model: mat4x4f, normal_local: vec3f) -> vec3f {
+    let normal_matrix = mat3x3f(inv_model[0].xyz, inv_model[1].xyz, inv_model[2].xyz);
+    return normalize(normal_matrix * normal_local);
+}
+
+// Spherical UV mapping (sphere or any radial surface)
+// Returns UV in [0,1] range
+fn spherical_uv(p: vec3f) -> vec2f {
+    let u = atan2(p.x, p.z) / TAU + 0.5;
+    let v = acos(clamp(p.y / length(p), -1.0, 1.0)) / PI;
+    return vec2f(u, v);
+}
+
+// Spherical UV from direction vector (for skybox, etc.)
+fn spherical_uv_from_dir(dir: vec3f) -> vec2f {
+    let u = atan2(dir.z, dir.x) / TAU + 0.5;
+    let v = asin(clamp(dir.y, -1.0, 1.0)) / PI + 0.5;
+    return vec2f(u, v);
+}
+
+// Grid pattern for procedural texturing (checkerboard-like)
+fn grid_pattern(uv: vec2f) -> f32 {
+    let grid = 0.5 + 0.5 * sin(uv.x * PI) * sin(uv.y * PI);
+    return smoothstep(0.45, 0.55, grid);
+}
+
+// NOTE: calc_sdf_normal_bumped() removed - too specialized, depends on get_dist()
+// from scene_query snippets. Keep bump mapping code inline in shaders that use it.
+
+// Calculates normalized screen coordinates from fragment position and resolution.
+// Input `p` is the fragment's @builtin(position), `resolution` is the screen resolution.
+// Returns a vec2f in NDC space, with X adjusted for aspect ratio.
+fn getScreenCoord(p: vec4f, resolution: vec2f) -> vec2f {
+    let q = p.xy / resolution;
+    var coord = -1.0 + 2.0 * q;
+    coord.x *= resolution.x / resolution.y;
+    return coord;
+}