Handle VMM WCS edge grid rounding

backend/tests/test_sprint208_vmm_flood_hazard.py

@@ -5,7 +5,6 @@ from uuid import uuid4
 
 import numpy as np
 import pytest
-import rasterio
 from fastapi.testclient import TestClient
 from pyproj import Transformer
 from rasterio.io import MemoryFile
@@ -104,6 +103,23 @@ def depth_tiff(*, normalized_metres: bool = False) -> bytes:
         return memory.read()
 
 
+def edge_depth_tiff(*, left: float, top: float, x_resolution: float, y_resolution: float = 5.0) -> bytes:
+    values = np.full((20, 20), 100.0, dtype="float32")
+    with MemoryFile() as memory:
+        with memory.open(
+            driver="GTiff",
+            width=20,
+            height=20,
+            count=1,
+            dtype="float32",
+            crs="EPSG:31370",
+            transform=from_origin(left, top, x_resolution, y_resolution),
+            nodata=0.0,
+        ) as output:
+            output.write(values, 1)
+        return memory.read()
+
+
 def test_flood_hazard_registry_is_complete_and_semantically_honest() -> None:
     products = FloodHazardAcquisitionService.list_products()
 
@@ -151,6 +167,39 @@ def test_flood_hazard_tiles_stay_below_the_observed_vmm_coverage_limit() -> None
     )
 
 
+def test_flood_hazard_mosaic_harmonizes_only_bounded_wcs_edge_grid_rounding() -> None:
+    regular = edge_depth_tiff(left=200_000, top=210_100, x_resolution=5.0)
+    rounded_edge = edge_depth_tiff(
+        left=200_100,
+        top=210_100,
+        x_resolution=4.76555,
+        y_resolution=5.0008,
+    )
+    diagnostics: dict[str, object] = {}
+
+    mosaic = FloodHazardAcquisitionService._mosaic_geotiffs(
+        [regular, rounded_edge],
+        expected_resolution_m=5.0,
+        diagnostics=diagnostics,
+    )
+
+    with MemoryFile(mosaic) as memory, memory.open() as dataset:
+        assert dataset.res == pytest.approx((5.0, 5.0))
+    assert diagnostics["harmonized_tile_indexes"] == [1]
+    assert diagnostics["harmonization_method"] == "rasterio_merge_target_resolution"
+
+    unsafe_edge = edge_depth_tiff(left=200_100, top=210_100, x_resolution=4.5)
+    with pytest.raises(AppError) as exc_info:
+        FloodHazardAcquisitionService._mosaic_geotiffs(
+            [regular, unsafe_edge],
+            expected_resolution_m=5.0,
+        )
+    assert exc_info.value.code == "FLOOD_HAZARD_TILE_MISMATCH"
+    assert exc_info.value.details["invalid_resolution_tiles"] == [
+        {"tile_index": 1, "resolution": [4.5, 5.0]}
+    ]
+
+
 def test_flood_hazard_xml_provider_error_is_exposed_without_losing_the_canonical_error() -> None:
     response = b"""<?xml version="1.0"?>
     <ExceptionReport xmlns="http://www.opengis.net/ows/1.1">