V13-FE-011: finalize search list layout slice

docs/Design/kbx-foundation-v36/backend/Shared/Excel/ImportMappingSuggestions.cs

@@ -0,0 +1,36 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Shared.Excel;
+
+public static class ImportSourceSignature
+{
+    public static string Create(IEnumerable<string> columns)
+    {
+        var canonical = string.Join("|", columns.Select(Normalize).Order(StringComparer.Ordinal));
+        return Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(canonical))).ToLowerInvariant();
+    }
+
+    private static string Normalize(string value) =>
+        new(value.Where(char.IsLetterOrDigit).Select(char.ToLowerInvariant).ToArray());
+}
+
+public interface IImportMappingSuggester
+{
+    Task<IReadOnlyList<ImportMapping>> SuggestAsync(
+        IReadOnlyList<string> unmappedColumns,
+        ImportDefinition definition,
+        CancellationToken ct);
+}
+
+/// <summary>
+/// Safe default. A production AI adapter can replace this registration. The adapter must return
+/// only target fields present in ImportDefinition and never mutate data or persist a mapping by itself.
+/// </summary>
+public sealed class NoopImportMappingSuggester : IImportMappingSuggester
+{
+    public Task<IReadOnlyList<ImportMapping>> SuggestAsync(
+        IReadOnlyList<string> unmappedColumns,
+        ImportDefinition definition,
+        CancellationToken ct) => Task.FromResult<IReadOnlyList<ImportMapping>>([]);
+}