feat(worker): resolve and seed session skills before each run

tests/ClaudeDo.Worker.Tests/Runner/SkillResolutionTests.cs

@@ -0,0 +1,44 @@
+using ClaudeDo.Worker.Runner;
+using Xunit;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+public class SkillResolutionTests
+{
+    [Fact]
+    public void Null_and_empty_sources_contribute_nothing()
+        => Assert.Empty(TaskRunner.UnionSkillNames(null, "", "   ", "[]"));
+
+    [Fact]
+    public void Single_source_is_returned_in_order()
+        => Assert.Equal(["a", "b"], TaskRunner.UnionSkillNames("""["a","b"]"""));
+
+    [Fact]
+    public void Unions_across_task_list_global_levels()
+    {
+        var result = TaskRunner.UnionSkillNames("""["a"]""", """["b"]""", """["c"]""");
+        Assert.Equal(["a", "b", "c"], result);
+    }
+
+    [Fact]
+    public void Dedups_ordinal_preserving_first_occurrence_order()
+    {
+        var result = TaskRunner.UnionSkillNames("""["a","b"]""", """["b","c"]""", """["a","d"]""");
+        Assert.Equal(["a", "b", "c", "d"], result);
+    }
+
+    [Fact]
+    public void Dedup_is_case_sensitive_ordinal()
+    {
+        var result = TaskRunner.UnionSkillNames("""["Foo"]""", """["foo"]""");
+        Assert.Equal(["Foo", "foo"], result);
+    }
+
+    [Fact]
+    public void Malformed_json_is_ignored_not_thrown()
+        => Assert.Equal(["a"], TaskRunner.UnionSkillNames("not json", """["a"]"""));
+
+    [Fact]
+    public void Blank_entries_within_array_are_skipped()
+        => Assert.Equal(["a"], TaskRunner.UnionSkillNames("""["a", "", "   ", null]"""));
+}