Make it so CONFIG_DIR is not in the list of writable roots by default (#419)

To play it safe, let's keep `CONFIG_DIR` out of the default list of
writable roots.

This also fixes an issue where `execWithSeatbelt()` was modifying
`writableRoots` instead of creating a new array.

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* #423
* #420
* __->__ #419

codex-cli/src/utils/agent/sandbox/raw-exec.ts

@@ -21,7 +21,7 @@ const MAX_BUFFER = 1024 * 100; // 100 KB
 export function exec(
   command: Array<string>,
   options: SpawnOptions,
-  _writableRoots: Array<string>,
+  _writableRoots: ReadonlyArray<string>,
   abortSignal?: AbortSignal,
 ): Promise<ExecResult> {
   // Adapt command for the current platform (e.g., convert 'ls' to 'dir' on Windows)