test(quality): cover sqlite redis and overlay edge branches

internal/overlay/executor_test.go

@@ -243,9 +243,41 @@ func TestApplyRejectsExistingOutputDir(t *testing.T) {
 	}
 }
 
+func TestApplyRejectsSourceFile(t *testing.T) {
+	sourceDir := filepath.Join(t.TempDir(), "source.txt")
+	if err := os.WriteFile(sourceDir, []byte("not a dir"), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	_, err := Apply(context.Background(), ApplyRequest{
+		PackDir:   t.TempDir(),
+		SourceDir: sourceDir,
+		Overlays:  []pack.HostOverlay{{OverlayID: "sample", PatchPath: "overlays/sample.patch"}},
+	})
+	if err == nil || !strings.Contains(err.Error(), "must be a directory") {
+		t.Fatalf("Apply() error = %v, want source dir rejection", err)
+	}
+}
+
 func TestCopyFileRejectsMissingSource(t *testing.T) {
 	err := copyFile(filepath.Join(t.TempDir(), "missing.txt"), filepath.Join(t.TempDir(), "target.txt"), 0o644)
 	if err == nil {
 		t.Fatal("copyFile() error = nil, want missing source failure")
 	}
 }
+
+func TestCopyFileRejectsTargetParentThatIsAFile(t *testing.T) {
+	parentFile := filepath.Join(t.TempDir(), "parent-file")
+	if err := os.WriteFile(parentFile, []byte("block mkdir"), 0o644); err != nil {
+		t.Fatalf("WriteFile(parentFile) error = %v", err)
+	}
+	sourcePath := filepath.Join(t.TempDir(), "source.txt")
+	if err := os.WriteFile(sourcePath, []byte("hello"), 0o644); err != nil {
+		t.Fatalf("WriteFile(sourcePath) error = %v", err)
+	}
+
+	err := copyFile(sourcePath, filepath.Join(parentFile, "nested", "target.txt"), 0o644)
+	if err == nil {
+		t.Fatal("copyFile() error = nil, want parent path mkdir failure")
+	}
+}