Rescue graph building test into subcommand

Sources/dpk-cli/TextFileWriter.swift

@@ -0,0 +1,29 @@
+/*
+ * darwin-apk © 2024 Gay Pizza Specifications
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import Foundation
+import Darwin
+
+struct TextFileWriter: TextOutputStream {
+  private var _hnd: FileHandle
+
+  init?(_ to: URL) {
+    let file = open(to.path(), O_WRONLY | O_CREAT | O_TRUNC | O_SYNC, 0o644)
+    guard file >= 0 else {
+      return nil
+    }
+    self._hnd = FileHandle(fileDescriptor: file, closeOnDealloc: true)
+  }
+
+  mutating func write(_ string: String) {
+    if let data = string.data(using: .utf8) {
+      try? self._hnd.write(contentsOf: data)
+    }
+  }
+
+  mutating func close() throws {
+    try self._hnd.close()
+  }
+}