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 {

codex-rs/exec/src/cli.rs

@@ -1,3 +1,5 @@
+use clap::Args;
+use clap::FromArgMatches;
 use clap::Parser;
 use clap::ValueEnum;
 use codex_common::CliConfigOverrides;
@@ -108,20 +110,22 @@ pub enum Command {
     Review(ReviewArgs),
 }
 
-#[derive(Parser, Debug)]
-pub struct ResumeArgs {
+#[derive(Args, Debug)]
+struct ResumeArgsRaw {
+    // Note: This is the direct clap shape. We reinterpret the positional when --last is set
+    // so "codex resume --last <prompt>" treats the positional as a prompt, not a session id.
     /// Conversation/session id (UUID). When provided, resumes this session.
     /// If omitted, use --last to pick the most recent recorded session.
     #[arg(value_name = "SESSION_ID")]
-    pub session_id: Option<String>,
+    session_id: Option<String>,
 
     /// Resume the most recent recorded session (newest) without specifying an id.
     #[arg(long = "last", default_value_t = false)]
-    pub last: bool,
+    last: bool,
 
     /// Show all sessions (disables cwd filtering).
     #[arg(long = "all", default_value_t = false)]
-    pub all: bool,
+    all: bool,
 
     /// Optional image(s) to attach to the prompt sent after resuming.
     #[arg(
@@ -131,13 +135,72 @@ pub struct ResumeArgs {
         value_delimiter = ',',
         num_args = 1
     )]
-    pub images: Vec<PathBuf>,
+    images: Vec<PathBuf>,
 
     /// Prompt to send after resuming the session. If `-` is used, read from stdin.
     #[arg(value_name = "PROMPT", value_hint = clap::ValueHint::Other)]
+    prompt: Option<String>,
+}
+
+#[derive(Debug)]
+pub struct ResumeArgs {
+    /// Conversation/session id (UUID). When provided, resumes this session.
+    /// If omitted, use --last to pick the most recent recorded session.
+    pub session_id: Option<String>,
+
+    /// Resume the most recent recorded session (newest) without specifying an id.
+    pub last: bool,
+
+    /// Show all sessions (disables cwd filtering).
+    pub all: bool,
+
+    /// Optional image(s) to attach to the prompt sent after resuming.
+    pub images: Vec<PathBuf>,
+
+    /// Prompt to send after resuming the session. If `-` is used, read from stdin.
     pub prompt: Option<String>,
 }
 
+impl From<ResumeArgsRaw> for ResumeArgs {
+    fn from(raw: ResumeArgsRaw) -> Self {
+        // When --last is used without an explicit prompt, treat the positional as the prompt
+        // (clap can’t express this conditional positional meaning cleanly).
+        let (session_id, prompt) = if raw.last && raw.prompt.is_none() {
+            (None, raw.session_id)
+        } else {
+            (raw.session_id, raw.prompt)
+        };
+        Self {
+            session_id,
+            last: raw.last,
+            all: raw.all,
+            images: raw.images,
+            prompt,
+        }
+    }
+}
+
+impl Args for ResumeArgs {
+    fn augment_args(cmd: clap::Command) -> clap::Command {
+        ResumeArgsRaw::augment_args(cmd)
+    }
+
+    fn augment_args_for_update(cmd: clap::Command) -> clap::Command {
+        ResumeArgsRaw::augment_args_for_update(cmd)
+    }
+}
+
+impl FromArgMatches for ResumeArgs {
+    fn from_arg_matches(matches: &clap::ArgMatches) -> Result<Self, clap::Error> {
+        ResumeArgsRaw::from_arg_matches(matches).map(Self::from)
+    }
+
+    fn update_from_arg_matches(&mut self, matches: &clap::ArgMatches) -> Result<(), clap::Error> {
+        *self = ResumeArgsRaw::from_arg_matches(matches).map(Self::from)?;
+        Ok(())
+    }
+}
+
 #[derive(Parser, Debug)]
 pub struct ReviewArgs {
     /// Review staged, unstaged, and untracked changes.