fix(setup): preserve symlinks in atomicWriteFile

Add ResolveForWrite helper that resolves symlinks before writing,
so atomic writes go to the symlink target instead of replacing
the symlink itself.

internal/utils/path_test.go

@@ -179,3 +179,54 @@ func TestCanonicalizePathSymlink(t *testing.T) {
 		}
 	}
 }
+
+func TestResolveForWrite(t *testing.T) {
+	t.Run("regular file", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		file := filepath.Join(tmpDir, "regular.txt")
+		if err := os.WriteFile(file, []byte("test"), 0644); err != nil {
+			t.Fatal(err)
+		}
+
+		got, err := ResolveForWrite(file)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got != file {
+			t.Errorf("got %q, want %q", got, file)
+		}
+	})
+
+	t.Run("symlink", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		target := filepath.Join(tmpDir, "target.txt")
+		if err := os.WriteFile(target, []byte("test"), 0644); err != nil {
+			t.Fatal(err)
+		}
+		link := filepath.Join(tmpDir, "link.txt")
+		if err := os.Symlink(target, link); err != nil {
+			t.Fatal(err)
+		}
+
+		got, err := ResolveForWrite(link)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got != target {
+			t.Errorf("got %q, want %q", got, target)
+		}
+	})
+
+	t.Run("non-existent", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		newFile := filepath.Join(tmpDir, "new.txt")
+
+		got, err := ResolveForWrite(newFile)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got != newFile {
+			t.Errorf("got %q, want %q", got, newFile)
+		}
+	})
+}