Fix resume --last with --json option (#9475)

Fix resume --last prompt parsing by dropping the clap conflict on the
codex resume subcommand so a positional prompt is accepted when --last
is set. This aligns interactive resume behavior with exec-mode logic and
avoids the “--last cannot be used with SESSION_ID” error.

This addresses #6717

codex-rs/cli/src/main.rs

@@ -147,7 +147,7 @@ struct ResumeCommand {
     session_id: Option<String>,
 
     /// Continue the most recent session without showing the picker.
-    #[arg(long = "last", default_value_t = false, conflicts_with = "session_id")]
+    #[arg(long = "last", default_value_t = false)]
     last: bool,
 
     /// Show all sessions (disables cwd filtering and shows CWD column).
@@ -932,6 +932,24 @@ mod tests {
         finalize_fork_interactive(interactive, root_overrides, session_id, last, all, fork_cli)
     }
 
+    #[test]
+    fn exec_resume_last_accepts_prompt_positional() {
+        let cli =
+            MultitoolCli::try_parse_from(["codex", "exec", "--json", "resume", "--last", "2+2"])
+                .expect("parse should succeed");
+
+        let Some(Subcommand::Exec(exec)) = cli.subcommand else {
+            panic!("expected exec subcommand");
+        };
+        let Some(codex_exec::Command::Resume(args)) = exec.command else {
+            panic!("expected exec resume");
+        };
+
+        assert!(args.last);
+        assert_eq!(args.session_id, None);
+        assert_eq!(args.prompt.as_deref(), Some("2+2"));
+    }
+
     fn app_server_from_args(args: &[&str]) -> AppServerCommand {
         let cli = MultitoolCli::try_parse_from(args).expect("parse");
         let Subcommand::AppServer(app_server) = cli.subcommand.expect("app-server present") else {