Introduce GEMINI_CLI_HOME for strict test isolation (#15907)

packages/core/src/utils/paths.ts

@@ -6,6 +6,7 @@
 
 import path from 'node:path';
 import os from 'node:os';
+import process from 'node:process';
 import * as crypto from 'node:crypto';
 
 export const GEMINI_DIR = '.gemini';
@@ -18,13 +19,33 @@ export const GOOGLE_ACCOUNTS_FILENAME = 'google_accounts.json';
  */
 export const SHELL_SPECIAL_CHARS = /[ \t()[\]{};|*?$`'"#&<>!~]/;
 
+/**
+ * Returns the home directory.
+ * If GEMINI_CLI_HOME environment variable is set, it returns its value.
+ * Otherwise, it returns the user's home directory.
+ */
+export function homedir(): string {
+  const envHome = process.env['GEMINI_CLI_HOME'];
+  if (envHome) {
+    return envHome;
+  }
+  return os.homedir();
+}
+
+/**
+ * Returns the operating system's default directory for temporary files.
+ */
+export function tmpdir(): string {
+  return os.tmpdir();
+}
+
 /**
  * Replaces the home directory with a tilde.
  * @param path - The path to tildeify.
  * @returns The tildeified path.
  */
 export function tildeifyPath(path: string): string {
-  const homeDir = os.homedir();
+  const homeDir = homedir();
   if (path.startsWith(homeDir)) {
     return path.replace(homeDir, '~');
   }