Implement final fixes and close out the implemetation roadmap

internal/framework/pipeline/runner_extract_handoff_test.go

@@ -135,6 +135,20 @@ func TestRunnerPassesIndependentConcreteMetadataToValidatorsAndExtractors(t *tes
 	}
 }
 
+func TestRunnerRejectsMetadataThatCannotBeCloned(t *testing.T) {
+	prepared := preparedAttemptDebugPipeline(t)
+	cyclic := make(map[string]any)
+	cyclic["self"] = cyclic
+	_, err := New().Run(context.Background(), RunInput{
+		Prepared: prepared,
+		RawInput: []byte("input"),
+		Metadata: map[string]any{"cyclic": cyclic},
+	})
+	if err == nil || !strings.Contains(err.Error(), "clone run metadata: metadata.cyclic.self contains a cycle") {
+		t.Fatalf("Run() error = %v, want contextual metadata clone failure", err)
+	}
+}
+
 func TestRunnerContinuesFromFreshAndReusedExtractResults(t *testing.T) {
 	prepared := preparedAttemptDebugPipeline(t)
 	extractCalls := 0