enable-resume (#3537)

Adding the ability to resume conversations.
we have one verb `resume`. 

Behavior:

`tui`:
`codex resume`: opens session picker
`codex resume --last`: continue last message
`codex resume <session id>`: continue conversation with `session id`

`exec`:
`codex resume --last`: continue last conversation
`codex resume <session id>`: continue conversation with `session id`

Implementation:
- I added a function to find the path in `~/.codex/sessions/` with a
`UUID`. This is helpful in resuming with session id.
- Added the above mentioned flags
- Added lots of testing

codex-rs/tui/src/cli.rs

@@ -13,35 +13,18 @@ pub struct Cli {
     #[arg(long = "image", short = 'i', value_name = "FILE", value_delimiter = ',', num_args = 1..)]
     pub images: Vec<PathBuf>,
 
-    /// Open an interactive picker to resume a previous session recorded on disk
-    /// instead of starting a new one.
-    ///
-    /// Notes:
-    /// - Mutually exclusive with `--continue`.
-    /// - The picker displays recent sessions and a preview of the first real user
-    ///   message to help you select the right one.
-    #[arg(
-        long = "resume",
-        default_value_t = false,
-        conflicts_with = "continue",
-        hide = true
-    )]
-    pub resume: bool,
+    // Internal controls set by the top-level `codex resume` subcommand.
+    // These are not exposed as user flags on the base `codex` command.
+    #[clap(skip)]
+    pub resume_picker: bool,
 
-    /// Continue the most recent conversation without showing the picker.
-    ///
-    /// Notes:
-    /// - Mutually exclusive with `--resume`.
-    /// - If no recorded sessions are found, this behaves like starting fresh.
-    /// - Equivalent to picking the newest item in the resume picker.
-    #[arg(
-        id = "continue",
-        long = "continue",
-        default_value_t = false,
-        conflicts_with = "resume",
-        hide = true
-    )]
-    pub r#continue: bool,
+    #[clap(skip)]
+    pub resume_last: bool,
+
+    /// Internal: resume a specific recorded session by id (UUID). Set by the
+    /// top-level `codex resume <SESSION_ID>` wrapper; not exposed as a public flag.
+    #[clap(skip)]
+    pub resume_session_id: Option<String>,
 
     /// Model the agent should use.
     #[arg(long, short = 'm')]

codex-rs/tui/src/lib.rs

@@ -15,6 +15,7 @@ use codex_core::config::SWIFTFOX_MEDIUM_MODEL;
 use codex_core::config::find_codex_home;
 use codex_core::config::load_config_as_toml_with_cli_overrides;
 use codex_core::config::persist_model_selection;
+use codex_core::find_conversation_path_by_id_str;
 use codex_core::protocol::AskForApproval;
 use codex_core::protocol::SandboxPolicy;
 use codex_ollama::DEFAULT_OSS_MODEL;
@@ -343,7 +344,16 @@ async fn run_ratatui_app(
         }
     }
 
-    let resume_selection = if cli.r#continue {
+    // Determine resume behavior: explicit id, then resume last, then picker.
+    let resume_selection = if let Some(id_str) = cli.resume_session_id.as_deref() {
+        match find_conversation_path_by_id_str(&config.codex_home, id_str).await? {
+            Some(path) => resume_picker::ResumeSelection::Resume(path),
+            None => {
+                error!("Error finding conversation path: {id_str}");
+                resume_picker::ResumeSelection::StartFresh
+            }
+        }
+    } else if cli.resume_last {
         match RolloutRecorder::list_conversations(&config.codex_home, 1, None).await {
             Ok(page) => page
                 .items
@@ -352,7 +362,7 @@ async fn run_ratatui_app(
                 .unwrap_or(resume_picker::ResumeSelection::StartFresh),
             Err(_) => resume_picker::ResumeSelection::StartFresh,
         }
-    } else if cli.resume {
+    } else if cli.resume_picker {
         match resume_picker::run_resume_picker(&mut tui, &config.codex_home).await? {
             resume_picker::ResumeSelection::Exit => {
                 restore();