Group the sources into aliased modules and lint with the published plugins

src/processes/child.ts

@@ -0,0 +1,30 @@
+// What the child process call sites share: the exit status, read right after
+// `spawn` so the exit event cannot pass unseen while the caller reads the
+// streams, and echoing output without outrunning a slow reader.
+import type { ChildProcess } from "node:child_process";
+import { once } from "node:events";
+import { constants } from "node:os";
+import type { Writable } from "node:stream";
+
+// Resolves once the process exits, before its streams close, with its exit
+// code, or with 128 plus the signal number if a signal killed it, as a shell
+// reports. A process that fails to start rejects with the spawn error.
+export function exitCode(child: ChildProcess): Promise<number> {
+  const code = new Promise<number>((resolve, reject) => {
+    child.once("error", reject);
+    child.once("exit", (exit, signal) => {
+      resolve(exit ?? (signal === null ? 1 : 128 + constants.signals[signal]));
+    });
+  });
+  // Callers await it after draining the streams; a failed start must not be
+  // reported as an unhandled rejection before then.
+  code.catch(() => {});
+  return code;
+}
+
+// Writes a chunk, waiting for the stream to drain when its buffer is full.
+export async function echo(stream: Writable, chunk: string | Uint8Array): Promise<void> {
+  if (!stream.write(chunk)) {
+    await once(stream, "drain");
+  }
+}