V13-FE-011: finalize search list layout slice

docs/Design/kbx-foundation-v36/backend/Shared/Experiments/KbxExperimentAssignmentPolicy.cs

@@ -0,0 +1,20 @@
+using System.Security.Cryptography;
+using System.Text;
+using Kbx.Shared.Experiments.Generated;
+namespace Kbx.Shared.Experiments;
+public static class KbxExperimentAssignmentPolicy
+{
+    public static bool IsEnrolled(Guid tenantId,Guid userId,string experimentId,int rolloutPercent) =>
+        rolloutPercent>0 && Bucket(tenantId,userId,experimentId,"enroll") < rolloutPercent*100;
+    public static string ChooseVariant(Guid tenantId,Guid userId,KbxExperimentDefinition definition)
+    {
+        var point=Bucket(tenantId,userId,definition.Id,"variant")%100,cumulative=0;
+        foreach(var item in definition.Variants){cumulative+=item.Weight;if(point<cumulative)return item.Key;}
+        return "control";
+    }
+    private static int Bucket(Guid tenantId,Guid userId,string experimentId,string purpose)
+    {
+        var bytes=SHA256.HashData(Encoding.UTF8.GetBytes($"{tenantId:N}|{userId:N}|{experimentId}|{purpose}|kbx-v1"));
+        return (int)(BitConverter.ToUInt32(bytes,0)%10000);
+    }
+}