[AZ-1126] Migrate capturedAt to DateTimeOffset

Co-authored-by: Cursor <cursoragent@cursor.com>

SatelliteProvider.Common/DTO/UavTileMetadata.cs

@@ -1,10 +1,11 @@
 using System.Text.Json.Serialization;
+using SatelliteProvider.Common.Json;
 
 namespace SatelliteProvider.Common.DTO;
 
-// AZ-488 / `uav-tile-upload.md` v1.0.0 — per-tile metadata supplied with each
-// batch item. `CapturedAt` is normalized to UTC by the upload handler before
-// reaching the persistence layer.
+// AZ-488 / `uav-tile-upload.md` — per-tile metadata supplied with each batch
+// item. `CapturedAt` is UTC-aware (`DateTimeOffset`) and normalized to UTC
+// before persistence (AZ-1126 / F-AZ810-2).
 //
 // AZ-503: `FlightId` is optional. When provided, two UAVs uploading the same
 // (z, x, y) cell from different flights coexist as distinct DB rows and write
@@ -27,7 +28,8 @@ public record UavTileMetadata
     [JsonRequired]
     public double TileSizeMeters { get; init; }
     [JsonRequired]
-    public DateTime CapturedAt { get; init; }
+    [JsonConverter(typeof(UtcOffsetRequiredDateTimeOffsetConverter))]
+    public DateTimeOffset CapturedAt { get; init; }
     public Guid? FlightId { get; init; }
 }
 

SatelliteProvider.Common/Json/UtcOffsetRequiredDateTimeOffsetConverter.cs

@@ -0,0 +1,43 @@
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Text.RegularExpressions;
+
+namespace SatelliteProvider.Common.Json;
+
+public sealed partial class UtcOffsetRequiredDateTimeOffsetConverter : JsonConverter<DateTimeOffset>
+{
+    [GeneratedRegex(@"T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2}|[+-]\d{4})$", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant)]
+    private static partial Regex ExplicitOffsetPattern();
+
+    public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        if (reader.TokenType != JsonTokenType.String)
+        {
+            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
+        }
+
+        var raw = reader.GetString();
+        if (string.IsNullOrWhiteSpace(raw))
+        {
+            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
+        }
+
+        if (!ExplicitOffsetPattern().IsMatch(raw))
+        {
+            throw new JsonException("`capturedAt` must include an explicit UTC offset (for example `Z` or `+00:00`).");
+        }
+
+        if (!DateTimeOffset.TryParse(raw, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind, out var parsed))
+        {
+            throw new JsonException("`capturedAt` could not be parsed as an ISO-8601 timestamp.");
+        }
+
+        return parsed.ToUniversalTime();
+    }
+
+    public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
+    {
+        writer.WriteStringValue(value.ToUniversalTime().ToString("O", CultureInfo.InvariantCulture));
+    }
+}