diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/SqlQueryPlan.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/SqlQueryPlan.cs
index 0d933d07..f586bbf6 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/SqlQueryPlan.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql/SqlQueryPlan.cs
@@ -51,6 +51,21 @@ public sealed record SqlQueryPlan(
     IReadOnlyList<SqlTagDefinition> Members,
     IReadOnlyList<string> SelectedColumns)
 {
+    // A plan is documented as safe to cache and reuse across polls, so it must not stay aliased to the
+    // planner's mutable working lists — an IReadOnlyList<T> holding a List<T> is downcastable, and a
+    // mutation would silently corrupt every later poll that reuses the plan. Snapshot at the boundary.
+    /// <summary>The parameter markers in <see cref="SqlText"/>, aligned with <see cref="Parameters"/>.</summary>
+    public IReadOnlyList<string> ParameterNames { get; } = [.. ParameterNames];
+
+    /// <summary>The values to bind, aligned with <see cref="ParameterNames"/>.</summary>
+    public IReadOnlyList<object?> Parameters { get; } = [.. Parameters];
+
+    /// <summary>The tags this plan feeds, in input order; duplicates preserved.</summary>
+    public IReadOnlyList<SqlTagDefinition> Members { get; } = [.. Members];
+
+    /// <summary>The bare SELECT-list column names, in result-set ordinal order.</summary>
+    public IReadOnlyList<string> SelectedColumns { get; } = [.. SelectedColumns];
+
     /// <summary>
     ///     The key column all members are matched on — <see langword="null"/> for any model but
     ///     <see cref="SqlTagModel.KeyValue"/>. Uniform across <see cref="Members"/> by the group-key invariant,
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Tests/SqlQueryPlanImmutabilityTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Tests/SqlQueryPlanImmutabilityTests.cs
new file mode 100644
index 00000000..b76ddd8a
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Sql.Tests/SqlQueryPlanImmutabilityTests.cs
@@ -0,0 +1,34 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Sql.Tests;
+
+public class SqlQueryPlanImmutabilityTests
+{
+    // A plan is documented as cacheable across polls. If it stayed aliased to the planner's working
+    // List<T>, a consumer downcast could corrupt every later poll that reused it.
+    [Fact]
+    public void Plan_doesNotAliasTheCallersLists()
+    {
+        var names = new List<string> { "@k0" };
+        var values = new List<object?> { "v" };
+        var members = new List<SqlTagDefinition>
+        {
+            new("raw", SqlTagModel.KeyValue, "t") { KeyColumn = "k", KeyValue = "v", ValueColumn = "c" },
+        };
+        var selected = new List<string> { "k", "c" };
+
+        var plan = new SqlQueryPlan(SqlTagModel.KeyValue, "gk", "SELECT 1", names, values, members, selected);
+
+        names.Add("@k1");
+        values.Add("other");
+        members.Add(members[0]);
+        selected.Add("extra");
+
+        plan.ParameterNames.Count.ShouldBe(1);
+        plan.Parameters.Count.ShouldBe(1);
+        plan.Members.Count.ShouldBe(1);
+        plan.SelectedColumns.Count.ShouldBe(2);
+    }
+}