fix(setup): preserve client config symlinks

src/application/ClientConfigPath.ts

@@ -0,0 +1,53 @@
+import { lstat, realpath } from "node:fs/promises";
+
+interface ClientConfigPathStats {
+  readonly uid?: number;
+  isFile?(): boolean;
+  isSymbolicLink(): boolean;
+}
+
+interface ClientConfigPathFileSystem {
+  lstat(path: string): Promise<ClientConfigPathStats>;
+  realpath?(path: string): Promise<string>;
+}
+
+const systemFileSystem: ClientConfigPathFileSystem = { lstat, realpath };
+
+/**
+ * Resolve an existing, user-owned config symlink to one stable transaction
+ * path. Missing regular paths remain eligible for first-run creation.
+ */
+export const resolveClientConfigTransactionPath = async (
+  requestedPath: string,
+  fileSystem: ClientConfigPathFileSystem = systemFileSystem,
+): Promise<string | undefined> => {
+  let requestedStats: ClientConfigPathStats;
+  try {
+    requestedStats = await fileSystem.lstat(requestedPath);
+  } catch (cause: unknown) {
+    return isMissing(cause) ? requestedPath : undefined;
+  }
+  if (!requestedStats.isSymbolicLink()) return requestedPath;
+
+  const currentUid =
+    typeof process.getuid === "function" ? process.getuid() : undefined;
+  if (
+    currentUid === undefined ||
+    requestedStats.uid !== currentUid ||
+    fileSystem.realpath === undefined
+  )
+    return undefined;
+
+  try {
+    const canonicalPath = await fileSystem.realpath(requestedPath);
+    const targetStats = await fileSystem.lstat(canonicalPath);
+    return targetStats.isFile?.() === true && targetStats.uid === currentUid
+      ? canonicalPath
+      : undefined;
+  } catch {
+    return undefined;
+  }
+};
+
+const isMissing = (cause: unknown): boolean =>
+  cause instanceof Error && "code" in cause && cause.code === "ENOENT";