SyncEngine fails to parse standard ISO8601 dates from CloudKit

[Armenm]

Description

When CloudKit returns dates in standard ISO8601 format (e.g., 2026-03-21T03:57:40.026Z), SyncEngine fails to parse them with the error:

Cannot parse 2026-03-21T03:57:40.026Z. String should adhere to the preferred format of the locale, such as 2026-03-21 03:57:40.

Root Cause

The ISO8601.swift internal helpers use a non-standard date format:

// Current implementation (incorrect for CloudKit)
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss.SSS"  // Space separator, no timezone

// On iOS 15+
.dateTimeSeparator(.space)  // Also expects space instead of 'T'

But CloudKit returns standard ISO8601 with T separator and Z timezone suffix:

• 2026-03-21T03:57:40.026Z

Suggested Fix

Update ISO8601.swift to handle the standard format:

extension DateFormatter {
  fileprivate static let iso8601Fractional: DateFormatter = {
    let formatter = DateFormatter()
    formatter.calendar = Calendar(identifier: .iso8601)
    formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"  // Standard ISO8601
    formatter.locale = Locale(identifier: "en_US_POSIX")
    formatter.timeZone = TimeZone(secondsFromGMT: 0)
    return formatter
  }()
}

@available(iOS 15, macOS 12, tvOS 15, watchOS 8, *)
extension Date.ISO8601FormatStyle {
  fileprivate func currentTimestamp(includingFractionalSeconds: Bool) -> Self {
    year().month().day()
      .dateTimeSeparator(.standard)  // Use 'T' separator
      .time(includingFractionalSeconds: includingFractionalSeconds)
      .timeZone(separator: .omitted)  // Handle 'Z' suffix
  }
}

Alternatively, the parser should try both formats - space-separated (for SQLite storage) and standard ISO8601 (for CloudKit).

Reproducibility

1. Create a @Table with a Date field
2. Sync to CloudKit via SyncEngine
3. On a different device, attempt to sync down the record
4. Date parsing fails with the above error

Environment

• sqlite-data: 1.6.0
• iOS/macOS: 17+/14+
• CloudKit: Private database