diff --git a/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/Internal/JintExtensions.cs b/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/Internal/JintExtensions.cs
index 7787448fe..2dc19097d 100644
--- a/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/Internal/JintExtensions.cs
+++ b/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/Internal/JintExtensions.cs
@@ -7,6 +7,7 @@
 
 using Jint;
 using Jint.Native;
+using Jint.Runtime.Interop;
 using Squidex.Infrastructure;
 
 namespace Squidex.Domain.Apps.Core.Scripting.Internal;
@@ -73,7 +74,10 @@ public static class JintExtensions
         {
             foreach (var (key, item) in vars)
             {
-                engine.SetValue(key, item);
+                // Deferred instead of Engine.SetValue, which maps every variable now. The global itself is
+                // installed eagerly, so existence checks and enumeration see the name without materializing
+                // anything; only the mapping waits for the first read of the value.
+                engine.Advanced.AddLazyGlobal(key, e => MapVariable(e, item));
             }
         }
 
@@ -81,4 +85,18 @@ public static class JintExtensions
 
         return context;
     }
+
+    /// <summary>
+    /// The conversion <see cref="Engine.SetValue(string, object)"/> performs, including its special case for
+    /// a CLR type, so deferring a variable cannot change what the script sees.
+    /// </summary>
+    private static JsValue MapVariable(Engine engine, object? item)
+    {
+        if (item is Type type)
+        {
+            return TypeReference.CreateTypeReference(engine, type);
+        }
+
+        return JsValue.FromObject(engine, item);
+    }
 }
diff --git a/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/WritableContext.cs b/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/WritableContext.cs
index a04b3a255..3ccfcab70 100644
--- a/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/WritableContext.cs
+++ b/backend/src/Squidex.Domain.Apps.Core.Operations/Scripting/WritableContext.cs
@@ -1,4 +1,4 @@
-// ==========================================================================
+// ==========================================================================
 //  Squidex Headless CMS
 // ==========================================================================
 //  Copyright (c) Squidex UG (haftungsbeschraenkt)
@@ -8,6 +8,7 @@
 using Jint;
 using Jint.Native;
 using Jint.Native.Object;
+using Jint.Runtime.Descriptors;
 
 namespace Squidex.Domain.Apps.Core.Scripting;
 
@@ -20,9 +21,17 @@ internal sealed class WritableContext : ObjectInstance
     {
         this.vars = vars;
 
+        // Scripts touch a fraction of the variables, but mapping one is not always cheap: a content data
+        // variable builds a wrapper, a user variable walks and groups every claim. The descriptors are
+        // installed eagerly - so key order, enumeration and existence checks are exactly what they were -
+        // and only the mapping waits for the first read of a value. Once it has run the descriptor drops
+        // back to an ordinary data property and rejoins the write inline cache, which is what a
+        // hand-written CustomJsValue descriptor cannot do.
         foreach (var (key, item) in vars)
         {
-            base.Set(key, FromObject(engine, item), this);
+            SetOwnProperty(key, PropertyDescriptor.CreateLazy(
+                (Engine: engine, Item: item),
+                static state => FromObject(state.Engine, state.Item)));
         }
     }
 
diff --git a/backend/tests/Squidex.Domain.Apps.Core.Tests/Operations/Scripting/JintScriptEngineTests.cs b/backend/tests/Squidex.Domain.Apps.Core.Tests/Operations/Scripting/JintScriptEngineTests.cs
index 365f44cb3..fec93fd7b 100644
--- a/backend/tests/Squidex.Domain.Apps.Core.Tests/Operations/Scripting/JintScriptEngineTests.cs
+++ b/backend/tests/Squidex.Domain.Apps.Core.Tests/Operations/Scripting/JintScriptEngineTests.cs
@@ -1047,6 +1047,153 @@ public class JintScriptEngineTests : IClassFixture<TranslationsFixture>
         Assert.Equal(JsonValue.Create("number,json,user"), actual);
     }
 
+    [Fact]
+    public void Should_not_map_unread_variable()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["number"] = 13,
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                number + 1;
+            ";
+
+        var actual = sut.Execute(vars, script);
+
+        Assert.Equal(JsonValue.Create(14), actual);
+        Assert.Equal(0, principal.Reads);
+    }
+
+    [Fact]
+    public void Should_see_unread_variable_in_enumeration()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                ('user' in globalThis) + ',' + (Object.getOwnPropertyNames(globalThis).indexOf('user') >= 0);
+            ";
+
+        var actual = sut.Execute(vars, script);
+
+        Assert.Equal(JsonValue.Create("true,true"), actual);
+        Assert.Equal(0, principal.Reads);
+    }
+
+    [Fact]
+    public void Should_map_variable_on_first_read()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                user.id;
+            ";
+
+        var actual = sut.Execute(vars, script);
+
+        Assert.Equal(JsonValue.Create("user1"), actual);
+        Assert.True(principal.Reads > 0);
+    }
+
+    [Fact]
+    public void Should_not_map_unread_context_variable()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["number"] = 13,
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                ctx.number + 1;
+            ";
+
+        var actual = sut.Execute(vars, script, new ScriptOptions { AsContext = true });
+
+        Assert.Equal(JsonValue.Create(14), actual);
+        Assert.Equal(0, principal.Reads);
+    }
+
+    [Fact]
+    public void Should_see_unread_context_variable_in_enumeration()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["number"] = 13,
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                Object.keys(ctx).join(',') + '|' + ('user' in ctx);
+            ";
+
+        var actual = sut.Execute(vars, script, new ScriptOptions { AsContext = true });
+
+        Assert.Equal(JsonValue.Create("number,user|true"), actual);
+        Assert.Equal(0, principal.Reads);
+    }
+
+    [Fact]
+    public void Should_map_context_variable_on_first_read()
+    {
+        var principal = new CountingPrincipal();
+
+        var vars = new ScriptVars
+        {
+            ["user"] = principal,
+        };
+
+        const string script = @"
+                ctx.user.id;
+            ";
+
+        var actual = sut.Execute(vars, script, new ScriptOptions { AsContext = true });
+
+        Assert.Equal(JsonValue.Create("user1"), actual);
+        Assert.True(principal.Reads > 0);
+    }
+
+    private sealed class CountingPrincipal : ClaimsPrincipal
+    {
+        public int Reads { get; private set; }
+
+        public CountingPrincipal()
+            : base(new ClaimsIdentity(
+            [
+                new Claim(OpenIdClaims.Subject, "user1"),
+                new Claim(OpenIdClaims.Name, "user"),
+            ], "Squidex"))
+        {
+        }
+
+        public override IEnumerable<Claim> Claims
+        {
+            get
+            {
+                Reads++;
+
+                return base.Claims;
+            }
+        }
+    }
+
     private static ScriptVars CreateVars()
     {
         return new ScriptVars