feat: wire ephemeral in codex exec (#10758)

codex-rs/exec/src/lib.rs

@@ -103,6 +103,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         cwd,
         skip_git_repo_check,
         add_dir,
+        ephemeral,
         color,
         last_message_file,
         json: json_mode,
@@ -254,7 +255,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         include_apply_patch_tool: None,
         show_raw_agent_reasoning: oss.then_some(true),
         tools_web_search_request: None,
-        ephemeral: None,
+        ephemeral: ephemeral.then_some(true),
         additional_writable_roots: add_dir,
     };