Sprint 3 — Must Feature 5종 추가 (상부→하부 순서)

상부 구조물:
- DeckSlabIR + DeckSlabBuilder + 기하학 (직사각형 슬래브 스위프)

연결부:
- BearingIR + BearingBuilder (카탈로그 기반, KDS 기본값 포함)

하부 구조물:
- PierIR + PierBuilder + 기하학 (다주 지원, 코핑 포함)
- AbutmentIR + AbutmentBuilder + 기하학 (흉벽 + 기초 + 날개벽)

core에 BearingType·PierType·ColumnShape·AbutmentType 열거형 추가
kernel: sweep.rs 공유 모듈 (sweep_profile_flat·box·prism·merge)
psc_i.rs → sweep.rs 의존으로 리팩터
GeomKernel trait에 4개 메서드 추가 (상부→하부 문서화 주석)

cargo test 57개 전부 통과

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cimery/crates/kernel/src/abutment.rs

@@ -0,0 +1,81 @@
+//! Abutment geometry — PureRustKernel.
+//! Breast wall + footing + wing walls (simplified rectangular shapes).
+
+use cimery_ir::AbutmentIR;
+use crate::{KernelError, Mesh, sweep};
+
+pub fn build_abutment_mesh(ir: &AbutmentIR) -> Result<Mesh, KernelError> {
+    if ir.breast_wall_height <= 0.0 {
+        return Err(KernelError::InvalidInput(
+            format!("breast_wall_height must be > 0, got {}", ir.breast_wall_height),
+        ));
+    }
+
+    let bw_h  = ir.breast_wall_height as f32;
+    let bw_t  = ir.breast_wall_thickness as f32;
+    let bw_w  = ir.breast_wall_width as f32;
+    let ft_l  = ir.footing_length as f32;
+    let ft_w  = ir.footing_width as f32;
+    let ft_t  = ir.footing_thickness as f32;
+
+    let mut parts: Vec<Mesh> = Vec::new();
+
+    // Breast wall: along transverse (Z), thickness along span (X), height (Y)
+    parts.push(sweep::centred_box(0.0, bw_h * 0.5, bw_t * 0.5, bw_h * 0.5, bw_w));
+
+    // Footing: below grade, spans along X (span direction)
+    {
+        let profile = vec![
+            [-ft_l * 0.5, -ft_t],
+            [ ft_l * 0.5, -ft_t],
+            [ ft_l * 0.5,  0.0 ],
+            [-ft_l * 0.5,  0.0 ],
+        ];
+        parts.push(sweep::sweep_profile_flat(&profile, ft_w));
+    }
+
+    // Wing walls (left and right)
+    for side in [&ir.wing_wall_left, &ir.wing_wall_right] {
+        let wl = side.length as f32;
+        let wh = side.height as f32;
+        let wt = side.thickness as f32;
+        // Simplified: vertical rectangle, oriented in XY, length along Z
+        parts.push(sweep::centred_box(0.0, wh * 0.5, wt * 0.5, wh * 0.5, wl));
+    }
+
+    Ok(sweep::merge_meshes(parts))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use cimery_core::{AbutmentType, MaterialGrade};
+    use cimery_ir::{AbutmentIR, FeatureId, WingWallIR};
+
+    fn test_ir() -> AbutmentIR {
+        let wing = WingWallIR { length: 4000.0, height: 3000.0, thickness: 500.0 };
+        AbutmentIR {
+            id: FeatureId::new(),
+            station: 0.0, skew_angle: 0.0,
+            abutment_type: AbutmentType::ReverseT,
+            breast_wall_height: 5000.0, breast_wall_thickness: 800.0,
+            breast_wall_width: 12000.0,
+            footing_length: 4000.0, footing_width: 13000.0, footing_thickness: 1000.0,
+            wing_wall_left: wing.clone(), wing_wall_right: wing,
+            material: MaterialGrade::C40,
+        }
+    }
+
+    #[test]
+    fn produces_mesh() {
+        let mesh = build_abutment_mesh(&test_ir()).unwrap();
+        assert!(mesh.triangle_count() > 0);
+    }
+
+    #[test]
+    fn zero_height_fails() {
+        let mut ir = test_ir();
+        ir.breast_wall_height = 0.0;
+        assert!(build_abutment_mesh(&ir).is_err());
+    }
+}