refactor(B04): 배수유역 라우터 700줄 분리 (동작 불변)

B04_PreProcess_Router_Watershed.py 714줄 -> 518줄. 산출물 기록(.npz·스테이지 기하)과
응답 좌표 변환 헬퍼 9개를 B04_PreProcess_Router_Watershed_Output.py(225줄)로 그대로 옮김.
공개 심볼 router · get_primary_region · CONTOUR_FILE · STREAM_FILE 유지
(main.py · B03_FileInput_Service_Chain · B07_DesignDetail_Router_Support 참조).

검증: ruff check 전체 통과·format 적용, tmp/tests 183 passed, 백엔드 재시작 후
경로 2개 유지, /drainage/rainfall 200, /drainage/primary-region 200(schema_version 3),
B05 화면 유역 11개·측점 66개 정상, 옮긴 순수 헬퍼 6개 직접 호출 스모크 통과.
분석 재실행(쓰기 경로)은 작업본 산출물을 덮어써서 돌리지 않음.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

B04_PreProcess/B04_PreProcess_Router_Watershed.py

@@ -8,7 +8,6 @@
 """
 
 import asyncio
-import base64
 import json
 import logging
 import math
@@ -16,33 +15,39 @@ from pathlib import Path
 from typing import Any
 from uuid import UUID
 
-import numpy as np
 from fastapi import APIRouter
 from fastapi.responses import JSONResponse
 from pyproj import Transformer
-from shapely.geometry import Point, Polygon, box
+from shapely.geometry import Point
 
 from B03_FileInput.B03_FileInput_Repository import get_project_storage_relative_path
 from B04_PreProcess.B04_PreProcess_Engine_Watershed_Analyze import preview_stages
 from B04_PreProcess.B04_PreProcess_Engine_Watershed_Export import (
     drainage_dir,
-    write_grid_arrays,
     write_stage,
 )
 from B04_PreProcess.B04_PreProcess_Engine_Watershed_Grid import (
-    AZIMUTH_INVALID,
-    AZIMUTH_SINK,
-    AZIMUTH_STEPS,
     mask_row_spans,
 )
+from B04_PreProcess.B04_PreProcess_Router_Watershed_Output import (
+    _as_polygons,
+    _boundary_geometry,
+    _flow_payload,
+    _grid_bbox_lonlat,
+    _grid_bbox_polygon,
+    _line_lonlat,
+    _polygon_rings,
+    _write_road_routing,
+    _write_stage_arrays,
+)
 from B05_Profile.B05_Profile_Repository import get_surface_crs_epsg
+from common_util.common_util_crs import resolve_project_crs
 from common_util.common_util_route_geometry import (
     StructureCandidate,
     find_planned_route_file,
     load_design_route,
     read_planned_route,
 )
-from common_util.common_util_crs import resolve_project_crs
 from common_util.common_util_storage import resolve_stored_project_path
 from common_util.common_util_surface_confirmation import get_surface_confirmation_params
 from common_util.common_util_wamis_rainfall import (
@@ -511,204 +516,3 @@ async def get_primary_region(
     # 응답 자체를 캐시로 남긴다 — 다음 조회는 배열을 재조립하지 않고 이 파일을 그대로 준다.
     _save_response(prepared["stored_path"], payload)
     return payload
-
-
-def _write_road_routing(
-    stored_path: str, preview: Any, spec: Any, route_line: Any, to_lonlat: Any
-) -> None:
-    """B05가 세부유역을 나눌 때 쓸 최소 산출물을 남긴다.
-
-    B05는 일반 사용자용이라 가벼워야 한다. 화살표(방향 코드)·밴드 표고 같은 확인용 배열은
-    빼고, **셀 → 도로 셀 귀속**과 도로 셀 제원만 담는다. 여기에 표고를 함께 넣는 이유는
-    유역 낙차를 내려면 셀 표고가 필요해서다(2026-07-31 사용자 지시).
-    """
-    routing = preview.routing
-    road = preview.road
-    if routing is None or road is None or road.count == 0:
-        return
-    write_grid_arrays(
-        stored_path,
-        "road_routing",
-        spec,
-        {
-            "road_slot": routing.road_slot,
-            "path_length": routing.path_length,
-            "strength": routing.strength,
-            "road_cell_index": road.cell_index,
-            "road_chainage": road.chainage,
-            "elevation": preview.terrain.elevation.reshape(-1),
-        },
-        {
-            "road_cells": road.count,
-            "reached_cells": int((routing.road_slot >= 0).sum()),
-            "basin_area_m2": round(preview.basin_area_m2, 1),
-            "pipe_count": len(preview.pipes),
-        },
-    )
-    # B05가 그대로 그릴 기하 — 계획도로선 · 기본 배관 · 2차 전체 배수유역, 이 셋뿐이다.
-    write_stage(
-        stored_path,
-        "road_routing",
-        {
-            "route": [route_line],
-            "basin_boundary": _boundary_geometry(preview.basin_boundary_xy),
-            "pipe": [
-                (
-                    Point(pipe.x, pipe.y),
-                    {"chainage_m": round(pipe.chainage_m, 2), "reason": pipe.reason},
-                )
-                for pipe in preview.pipes
-            ],
-            # 평균 흐름 화살표 — B05도 같은 그림을 그려야 하므로 여기 함께 남긴다.
-            "flow_arrow": [
-                (
-                    Point(x, y),
-                    {
-                        # B05 화면은 사업지 CRS(m)로 그리므로 미터 좌표도 함께 남긴다.
-                        "x": round(x, 2),
-                        "y": round(y, 2),
-                        "azimuth_deg": round(math.degrees(angle), 1),
-                        "reaches_road": reaches,
-                        "cells": cells,
-                    },
-                )
-                for x, y, angle, reaches, cells in preview.flow_arrows
-            ],
-        },
-        {
-            "basin_area_m2": round(preview.basin_area_m2, 1),
-            "pipe_count": len(preview.pipes),
-            "route_length_m": round(route_line.length, 1),
-            "arrow_count": len(preview.flow_arrows),
-            "arrow_spacing_m": DRAINAGE_ARROW_SPACING_M,
-        },
-        to_lonlat,
-    )
-
-
-def _write_stage_arrays(stored_path: str, preview: Any, domain: Any, spec: Any) -> None:
-    """격자 규모 배열(셀 마스크·흐름 방향·도달 여부)을 단계별 `.npz`로 남긴다."""
-    if domain is not None:
-        write_grid_arrays(
-            stored_path,
-            "primary_region",
-            spec,
-            {"mask": domain},
-            {
-                "cells": int(domain.sum()),
-                "bbox_cells": spec.size,
-                "expand_rounds": preview.expand_rounds,
-                "expand_closed": preview.expand_closed,
-            },
-        )
-    flow = preview.flow
-    if flow is None:
-        return
-    arrays = {
-        "direction": flow.direction.reshape(spec.n_rows, spec.n_cols),
-        "reaches_road": flow.reaches_road.reshape(spec.n_rows, spec.n_cols),
-        "analyzed": flow.analyzed.reshape(spec.n_rows, spec.n_cols),
-        # 사후 진단용 — 수신 셀이 있어야 사슬을 다시 따라가 볼 수 있다.
-        "receiver": preview.terrain.receiver.reshape(spec.n_rows, spec.n_cols),
-    }
-    if flow.burned is not None:
-        arrays["burned"] = flow.burned.reshape(spec.n_rows, spec.n_cols)
-    if preview.descent is not None:
-        arrays["band_elevation"] = preview.descent.band_elevation
-    # ⑥ 흐름 강도 곡선 — 기하가 아니라 수치 곡선이라 GeoJSON이 아닌 여기에 함께 담는다.
-    if preview.strength_profile:
-        curve = np.asarray(preview.strength_profile, dtype=np.float64)
-        arrays["strength_chainage_m"] = curve[:, 0]
-        arrays["strength_area_m2"] = curve[:, 1]
-    write_grid_arrays(
-        stored_path,
-        "flow_direction",
-        spec,
-        arrays,
-        {
-            "azimuth_steps": AZIMUTH_STEPS,
-            "sink_code": AZIMUTH_SINK,
-            "invalid_code": AZIMUTH_INVALID,
-            "analyzed": int(flow.analyzed.sum()),
-            "reaches_road": int((flow.reaches_road & flow.analyzed).sum()),
-            "no_road": int((~flow.reaches_road & flow.analyzed).sum()),
-            "burned": 0 if flow.burned is None else int(flow.burned.sum()),
-            "outer_seeds": flow.outer_seeds,
-            "interior_seeds": flow.interior_seeds,
-            "strength_points": len(preview.strength_profile),
-            "strength_total_m2": round(sum(area for _, area in preview.strength_profile), 1),
-        },
-    )
-
-
-def _flow_payload(preview: Any, domain: Any) -> dict[str, Any] | None:
-    """셀별 흐름 방향·도로 도달 여부를 바이트 배열로 압축한다.
-
-    셀이 수십만 개라 JSON 객체로는 못 보낸다. 셀 하나당 1바이트로 줄이고 base64로 싣는다:
-      하위 6비트(0x3F) = 32방위 코드(0~31, 0=화면 오른쪽·시계방향), 32=제자리, 33=표고 없음
-      최상위 비트(0x80) = 도로 도달(적색). 꺼져 있으면 미도달(백색 화살표).
-    바이트 순서는 `grid.row_spans`를 행 → 구간 → 열 오름차순으로 훑은 순서와 같다.
-    """
-    flow = preview.flow
-    if flow is None or domain is None:
-        return None
-    order = np.flatnonzero(domain.reshape(-1))
-    analyzed = flow.analyzed[order]
-    reaches = flow.reaches_road[order]
-    packed = np.clip(flow.direction[order], 0, AZIMUTH_INVALID).astype(np.uint8)
-    packed |= np.where(reaches, 0x80, 0).astype(np.uint8)
-    burned = flow.burned
-    return {
-        "encoding": "base64-uint8",
-        "azimuth_steps": AZIMUTH_STEPS,
-        "sink_code": AZIMUTH_SINK,
-        "invalid_code": AZIMUTH_INVALID,
-        "cells": int(order.size),
-        "reaches_road": int((reaches & analyzed).sum()),
-        "no_road": int((~reaches & analyzed).sum()),
-        # 격자에는 있으나 등고선 TIN 밖이라 표고가 없어 판정 못한 셀.
-        "unanalyzed": int((~analyzed).sum()),
-        # 확정된 상류 세류망을 따라 흐름을 강제로 새긴 셀 수.
-        "burned": 0 if burned is None else int(burned[order].sum()),
-        "outer_seeds": flow.outer_seeds,
-        "interior_seeds": flow.interior_seeds,
-        "data": base64.b64encode(packed.tobytes()).decode("ascii"),
-    }
-
-
-def _boundary_geometry(ring: list[tuple[float, float]]) -> list[Any]:
-    """2차 유역 외곽 링을 저장용 폴리곤으로 만든다(정점 3개 미만이면 비운다)."""
-    return [Polygon(ring)] if len(ring) >= 4 else []
-
-
-def _as_polygons(geometry: Any) -> list[Any]:
-    if geometry is None or geometry.is_empty:
-        return []
-    return list(geometry.geoms) if geometry.geom_type == "MultiPolygon" else [geometry]
-
-
-def _grid_bbox_polygon(spec: Any) -> Polygon:
-    x_max = spec.x_min + spec.n_cols * spec.cell_m
-    y_min = spec.y_max - spec.n_rows * spec.cell_m
-    return box(spec.x_min, y_min, x_max, spec.y_max)
-
-
-def _line_lonlat(line: Any, to_lonlat: Any) -> list[list[float]]:
-    return [list(to_lonlat(x, y)) for x, y in line.coords]
-
-
-def _polygon_rings(geometry: Any, to_lonlat: Any) -> list[list[list[float]]]:
-    """폴리곤/멀티폴리곤의 외곽 링만 뽑아 lonlat으로 바꾼다."""
-    if geometry is None or geometry.is_empty:
-        return []
-    parts = geometry.geoms if geometry.geom_type == "MultiPolygon" else [geometry]
-    return [[list(to_lonlat(x, y)) for x, y in part.exterior.coords] for part in parts]
-
-
-def _grid_bbox_lonlat(spec: Any, to_lonlat: Any) -> list[list[float]]:
-    x_min = spec.x_min
-    x_max = spec.x_min + spec.n_cols * spec.cell_m
-    y_max = spec.y_max
-    y_min = spec.y_max - spec.n_rows * spec.cell_m
-    corners = ((x_min, y_min), (x_min, y_max), (x_max, y_max), (x_max, y_min), (x_min, y_min))
-    return [list(to_lonlat(x, y)) for x, y in corners]