feat(commands): add /rename command to set a custom session title (#836)

* feat(commands): add /rename command to set a custom session title

Adds a `/rename <new title>` slash command that lets users set a
human-readable name for the current session. The new title is
persisted immediately to the session JSON file so it appears in
the session picker on the next open.

- Max title length capped at 100 characters (char-count aware, handles CJK)
- Errors on missing/empty arg or no active session
- Inner `rename_with_manager` helper keeps unit tests fully isolated
  from ~/.deepseek/sessions
- Localized descriptions in en, ja, zh-Hans, pt-BR

* fix(rename): sync App state before saving to prevent data loss

Use update_session() to merge current in-memory messages and tokens
into the session before writing the renamed title, preventing stale
disk data from overwriting unsaved App state.

* style: format rename command

---------

Co-authored-by: Hunter Bown <hmbown@gmail.com>

crates/tui/src/commands/mod.rs

@@ -18,6 +18,7 @@ mod network;
 mod note;
 mod provider;
 mod queue;
+mod rename;
 mod restore;
 mod review;
 mod session;
@@ -248,6 +249,12 @@ pub const COMMANDS: &[CommandInfo] = &[
         description_id: MessageId::CmdNetworkDescription,
     },
     // Session commands
+    CommandInfo {
+        name: "rename",
+        aliases: &[],
+        usage: "/rename <new title>",
+        description_id: MessageId::CmdRenameDescription,
+    },
     CommandInfo {
         name: "save",
         aliases: &[],
@@ -503,6 +510,7 @@ pub fn execute(cmd: &str, app: &mut App) -> CommandResult {
         "network" => network::network(app, arg),
 
         // Session commands
+        "rename" => rename::rename(app, arg),
         "save" => session::save(app, arg),
         "sessions" | "resume" => session::sessions(app, arg),
         "load" => session::load(app, arg),

crates/tui/src/commands/rename.rs

@@ -0,0 +1,183 @@
+//! `/rename` command — set a custom title for the current session.
+
+use crate::session_manager::{SessionManager, update_session};
+use crate::tui::app::App;
+
+use super::CommandResult;
+
+const MAX_TITLE_LEN: usize = 100;
+
+/// Rename the current session to the given title.
+///
+/// Usage: `/rename <new title>`
+///
+/// The new title is persisted immediately to `~/.deepseek/sessions/<id>.json`
+/// so the updated name is visible the next time the session picker is opened.
+pub fn rename(app: &mut App, arg: Option<&str>) -> CommandResult {
+    let new_title = match arg.map(str::trim).filter(|s| !s.is_empty()) {
+        Some(t) => t,
+        None => return CommandResult::error("Usage: /rename <new title>"),
+    };
+
+    if new_title.chars().count() > MAX_TITLE_LEN {
+        return CommandResult::error(format!("Title too long (max {MAX_TITLE_LEN} characters)"));
+    }
+
+    let session_id = match &app.current_session_id {
+        Some(id) => id.clone(),
+        None => {
+            return CommandResult::error(
+                "No active session. Send a message first to start a session.",
+            );
+        }
+    };
+
+    let manager = match SessionManager::default_location() {
+        Ok(m) => m,
+        Err(e) => return CommandResult::error(format!("Could not open sessions directory: {e}")),
+    };
+
+    rename_with_manager(new_title, &session_id, &manager, app)
+}
+
+fn rename_with_manager(
+    new_title: &str,
+    session_id: &str,
+    manager: &SessionManager,
+    app: &App,
+) -> CommandResult {
+    let mut session = match manager.load_session(session_id) {
+        Ok(s) => s,
+        Err(e) => return CommandResult::error(format!("Could not load session: {e}")),
+    };
+
+    // Sync with current App state to avoid overwriting unsaved messages.
+    session = update_session(
+        session,
+        &app.api_messages,
+        u64::from(app.session.total_tokens),
+        app.system_prompt.as_ref(),
+    );
+    session.metadata.title = new_title.to_string();
+
+    match manager.save_session(&session) {
+        Ok(_) => CommandResult::message(format!("Session renamed to \"{new_title}\"")),
+        Err(e) => CommandResult::error(format!("Could not save session: {e}")),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::config::Config;
+    use crate::session_manager::{SessionManager, create_saved_session_with_mode};
+    use crate::tui::app::{App, TuiOptions};
+    use tempfile::TempDir;
+
+    fn make_app(tmpdir: &TempDir) -> App {
+        App::new(
+            TuiOptions {
+                model: "deepseek-v4-pro".to_string(),
+                workspace: tmpdir.path().to_path_buf(),
+                config_path: None,
+                config_profile: None,
+                allow_shell: false,
+                use_alt_screen: true,
+                use_mouse_capture: false,
+                use_bracketed_paste: true,
+                max_subagents: 1,
+                skills_dir: tmpdir.path().join("skills"),
+                memory_path: tmpdir.path().join("memory.md"),
+                notes_path: tmpdir.path().join("notes.txt"),
+                mcp_config_path: tmpdir.path().join("mcp.json"),
+                use_memory: false,
+                start_in_agent_mode: false,
+                skip_onboarding: true,
+                yolo: false,
+                resume_session_id: None,
+                initial_input: None,
+            },
+            &Config::default(),
+        )
+    }
+
+    fn make_session_manager(tmpdir: &TempDir) -> SessionManager {
+        SessionManager::new(tmpdir.path().join("sessions")).unwrap()
+    }
+
+    #[test]
+    fn rename_without_arg_returns_error() {
+        let tmp = TempDir::new().unwrap();
+        let mut app = make_app(&tmp);
+        let r = rename(&mut app, None);
+        assert!(r.is_error);
+        assert!(r.message.unwrap().contains("Usage:"));
+    }
+
+    #[test]
+    fn rename_with_empty_arg_returns_error() {
+        let tmp = TempDir::new().unwrap();
+        let mut app = make_app(&tmp);
+        let r = rename(&mut app, Some("   "));
+        assert!(r.is_error);
+        assert!(r.message.unwrap().contains("Usage:"));
+    }
+
+    #[test]
+    fn rename_without_active_session_returns_error() {
+        let tmp = TempDir::new().unwrap();
+        let mut app = make_app(&tmp);
+        app.current_session_id = None;
+        let r = rename(&mut app, Some("My Session"));
+        assert!(r.is_error);
+        assert!(r.message.unwrap().contains("No active session"));
+    }
+
+    #[test]
+    fn rename_title_too_long_returns_error() {
+        let tmp = TempDir::new().unwrap();
+        let mut app = make_app(&tmp);
+        let long_title = "a".repeat(MAX_TITLE_LEN + 1);
+        let r = rename(&mut app, Some(&long_title));
+        assert!(r.is_error);
+        assert!(r.message.unwrap().contains("too long"));
+    }
+
+    #[test]
+    fn rename_persists_new_title() {
+        let tmp = TempDir::new().unwrap();
+        let manager = make_session_manager(&tmp);
+        let app = make_app(&tmp);
+
+        let session =
+            create_saved_session_with_mode(&[], "deepseek-v4-pro", tmp.path(), 0, None, None);
+        let session_id = session.metadata.id.clone();
+        manager.save_session(&session).unwrap();
+
+        let result = rename_with_manager("Brand New Title", &session_id, &manager, &app);
+        assert!(!result.is_error);
+        assert!(result.message.unwrap().contains("Brand New Title"));
+
+        let reloaded = manager.load_session(&session_id).unwrap();
+        assert_eq!(reloaded.metadata.title, "Brand New Title");
+    }
+
+    #[test]
+    fn rename_title_at_max_length_succeeds() {
+        let tmp = TempDir::new().unwrap();
+        let manager = make_session_manager(&tmp);
+        let app = make_app(&tmp);
+
+        let session =
+            create_saved_session_with_mode(&[], "deepseek-v4-pro", tmp.path(), 0, None, None);
+        let session_id = session.metadata.id.clone();
+        manager.save_session(&session).unwrap();
+
+        let max_title = "中".repeat(MAX_TITLE_LEN);
+        let result = rename_with_manager(&max_title, &session_id, &manager, &app);
+        assert!(!result.is_error);
+
+        let reloaded = manager.load_session(&session_id).unwrap();
+        assert_eq!(reloaded.metadata.title, max_title);
+    }
+}

crates/tui/src/localization.rs

@@ -247,6 +247,7 @@ pub enum MessageId {
     CmdProviderDescription,
     CmdQueueDescription,
     CmdRecallDescription,
+    CmdRenameDescription,
     CmdRestoreDescription,
     CmdRetryDescription,
     CmdReviewDescription,
@@ -435,6 +436,7 @@ pub const ALL_MESSAGE_IDS: &[MessageId] = &[
     MessageId::CmdProviderDescription,
     MessageId::CmdQueueDescription,
     MessageId::CmdRecallDescription,
+    MessageId::CmdRenameDescription,
     MessageId::CmdRestoreDescription,
     MessageId::CmdRetryDescription,
     MessageId::CmdReviewDescription,
@@ -758,6 +760,7 @@ fn english(id: MessageId) -> &'static str {
         }
         MessageId::CmdQueueDescription => "View or edit queued messages",
         MessageId::CmdRecallDescription => "Search prior cycle archives (BM25 over message text)",
+        MessageId::CmdRenameDescription => "Rename the current session",
         MessageId::CmdRestoreDescription => {
             "Roll back the workspace to a prior pre/post-turn snapshot. With no arg, lists recent snapshots."
         }
@@ -1039,6 +1042,7 @@ fn japanese(id: MessageId) -> Option<&'static str> {
         MessageId::CmdRecallDescription => {
             "過去のサイクルアーカイブを検索（メッセージ本文への BM25 検索）"
         }
+        MessageId::CmdRenameDescription => "現在のセッションの名前を変更",
         MessageId::CmdRestoreDescription => {
             "ワークスペースを以前のターン前/後スナップショットへロールバック。引数なしで最近のスナップショットを一覧表示。"
         }
@@ -1298,6 +1302,7 @@ fn chinese_simplified(id: MessageId) -> Option<&'static str> {
         MessageId::CmdProviderDescription => "切换或查看当前 LLM 后端（deepseek | nvidia-nim）",
         MessageId::CmdQueueDescription => "查看或编辑已排队的消息",
         MessageId::CmdRecallDescription => "搜索此前的循环归档（基于消息文本的 BM25 检索）",
+        MessageId::CmdRenameDescription => "重命名当前会话",
         MessageId::CmdRestoreDescription => {
             "将工作区回滚到此前的轮次前/后快照。不带参数时列出最近的快照。"
         }
@@ -1559,6 +1564,7 @@ fn portuguese_brazil(id: MessageId) -> Option<&'static str> {
         MessageId::CmdRecallDescription => {
             "Buscar arquivos de ciclos anteriores (BM25 sobre o texto das mensagens)"
         }
+        MessageId::CmdRenameDescription => "Renomear a sessão atual",
         MessageId::CmdRestoreDescription => {
             "Reverter o workspace a um snapshot pré/pós-turno anterior. Sem argumento, lista os snapshots recentes."
         }