diff --git a/src/ClaudeDo.Ui/Services/InheritanceResolver.cs b/src/ClaudeDo.Ui/Services/InheritanceResolver.cs
new file mode 100644
index 0000000..a62f3ec
--- /dev/null
+++ b/src/ClaudeDo.Ui/Services/InheritanceResolver.cs
@@ -0,0 +1,23 @@
+namespace ClaudeDo.Ui.Services;
+
+public enum InheritSource { Override, List, Global }
+
+public static class InheritanceResolver
+{
+    // Task-scope fields: task -> list -> global.
+    public static (string Value, InheritSource Source) Resolve(
+        string? taskValue, string? listValue, string? globalValue)
+    {
+        if (!string.IsNullOrWhiteSpace(taskValue)) return (taskValue!, InheritSource.Override);
+        if (!string.IsNullOrWhiteSpace(listValue)) return (listValue!, InheritSource.List);
+        return (globalValue ?? "", InheritSource.Global);
+    }
+
+    // List-scope fields: list -> global (lists have no tier above them).
+    public static (string Value, InheritSource Source) ResolveList(
+        string? listValue, string? globalValue)
+    {
+        if (!string.IsNullOrWhiteSpace(listValue)) return (listValue!, InheritSource.Override);
+        return (globalValue ?? "", InheritSource.Global);
+    }
+}
diff --git a/tests/ClaudeDo.Ui.Tests/InheritanceResolverTests.cs b/tests/ClaudeDo.Ui.Tests/InheritanceResolverTests.cs
new file mode 100644
index 0000000..706d2a5
--- /dev/null
+++ b/tests/ClaudeDo.Ui.Tests/InheritanceResolverTests.cs
@@ -0,0 +1,43 @@
+using ClaudeDo.Ui.Services;
+using Xunit;
+
+namespace ClaudeDo.Ui.Tests;
+
+public class InheritanceResolverTests
+{
+    [Fact]
+    public void Task_value_is_an_override()
+    {
+        var (value, source) = InheritanceResolver.Resolve("opus", "sonnet", "haiku");
+        Assert.Equal("opus", value);
+        Assert.Equal(InheritSource.Override, source);
+    }
+
+    [Fact]
+    public void Falls_through_to_list()
+    {
+        var (value, source) = InheritanceResolver.Resolve(null, "sonnet", "haiku");
+        Assert.Equal("sonnet", value);
+        Assert.Equal(InheritSource.List, source);
+    }
+
+    [Fact]
+    public void Falls_through_to_global()
+    {
+        var (value, source) = InheritanceResolver.Resolve("  ", null, "haiku");
+        Assert.Equal("haiku", value);
+        Assert.Equal(InheritSource.Global, source);
+    }
+
+    [Fact]
+    public void List_scope_treats_list_value_as_override()
+    {
+        var (value, source) = InheritanceResolver.ResolveList("sonnet", "haiku");
+        Assert.Equal("sonnet", value);
+        Assert.Equal(InheritSource.Override, source);
+
+        var (value2, source2) = InheritanceResolver.ResolveList(null, "haiku");
+        Assert.Equal("haiku", value2);
+        Assert.Equal(InheritSource.Global, source2);
+    }
+}