Sprint 6/7/8 — Alignment 로더 + CSV 라운드트립 + IncrementalDb 스캐폴드

Sprint 6 (Alignment JSON 로더):
- AlignmentIR: from_file(), position_at(station), total_length_m()
- AlignmentStation, AlignmentSpecs in ir crate
- alignments/BR-001-test.json: 40m 직선 테스트 선형

Sprint 7 (CSV 라운드트립):
- csv_template.rs: girder_params() 레지스트리
- girder_to_csv_template(): 헤더+기본값 CSV 출력
- girder_from_csv(): CSV → Vec<GirderIR> 파싱
- 테스트 3개 (template, multi-row, invalid span)

Sprint 8 (IncrementalDb 스캐폴드):
- incremental_scene.rs: IncrementalBridge<K>
- 안정적 girder ID (슬롯 기반), DB 캐시 → X-translate
- Sprint 9에서 전체 Feature IncrementalDb 통합 예정

cargo test 60개 전부 통과

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

cimery/crates/ir/src/lib.rs

@@ -138,6 +138,83 @@ pub struct SteelPlateIParams {
     pub web_thickness:    f64,
 }
 
+// ─── Alignment IR ────────────────────────────────────────────────────────────
+
+/// Single station point along an alignment.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AlignmentStation {
+    /// Station distance along alignment [m].
+    pub station: f64,
+    /// X coordinate [mm].
+    pub x:       f64,
+    /// Y coordinate [mm].
+    pub y:       f64,
+    /// Z coordinate [mm] — elevation.
+    pub z:       f64,
+}
+
+/// Road/bridge alignment specs.
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct AlignmentSpecs {
+    #[serde(default)]
+    pub r#type:        String,
+    #[serde(default)]
+    pub design_speed:  u32,     // km/h
+    #[serde(default)]
+    pub lanes:         u32,
+    #[serde(default)]
+    pub lane_width_mm: u32,
+}
+
+/// Alignment IR — parsed from cimery's own JSON format (ADR-002 R).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AlignmentIR {
+    pub name:               String,
+    #[serde(default)]
+    pub description:        String,
+    #[serde(default)]
+    pub coordinate_system:  String,
+    pub stations:           Vec<AlignmentStation>,
+    #[serde(default)]
+    pub specs:              AlignmentSpecs,
+}
+
+impl AlignmentIR {
+    /// Load from a cimery alignment JSON file.
+    pub fn from_file(path: impl AsRef<std::path::Path>) -> Result<Self, Box<dyn std::error::Error>> {
+        let s = std::fs::read_to_string(path)?;
+        Ok(serde_json::from_str(&s)?)
+    }
+
+    /// Total length in metres (last station - first station).
+    pub fn total_length_m(&self) -> f64 {
+        match (self.stations.first(), self.stations.last()) {
+            (Some(f), Some(l)) => l.station - f.station,
+            _ => 0.0,
+        }
+    }
+
+    /// Interpolate 3D position at a given station [m].
+    pub fn position_at(&self, station_m: f64) -> Option<[f64; 3]> {
+        if self.stations.len() < 2 { return None; }
+        let pts = &self.stations;
+        // Find surrounding segment
+        for i in 0..pts.len() - 1 {
+            let a = &pts[i];
+            let b = &pts[i + 1];
+            if station_m >= a.station && station_m <= b.station {
+                let t = (station_m - a.station) / (b.station - a.station);
+                return Some([
+                    a.x + t * (b.x - a.x),
+                    a.y + t * (b.y - a.y),
+                    a.z + t * (b.z - a.z),
+                ]);
+            }
+        }
+        None
+    }
+}
+
 // ─── Deck Slab IR ─────────────────────────────────────────────────────────────
 
 /// Fully-resolved Deck Slab (바닥판) specification.