feat(session): support --agent-cmd flag on wt session add

README.md

@@ -129,6 +129,7 @@ wt session [--mode M] ls  List workspaces in session
 wt session [--mode M] add <name>
       [-b base]           base: defaults to main
       [--panes 2|3]       override pane count (panes mode) / window count (windows mode)
+      [--agent-cmd <cmd>] override agent command for this invocation
       [--watch]           add status window with live agent status (panes mode only)
 wt session [--mode M] rm <name>
 wt session [--mode M] watch [-i N]
@@ -146,6 +147,7 @@ wt session [--mode M] ls            List workspaces in session
 wt session [--mode M] add <name>    Add a named session
      [-b <base>]                    Defaults to main
      [--panes 2|3]                  Override pane count (panes mode) / window count (windows mode)
+     [--agent-cmd <cmd>]            Override agent command for this invocation
      [--watch]                      Add status window with live agent status (panes mode only)
 wt session [--mode M] rm <name>     Remove a named session
 wt session [--mode M] watch [-i N]  Watch all the sessions
@@ -162,6 +164,7 @@ Manage multiple workspaces in tmux with dedicated agent, terminal, and optional
 # Add workspaces to session
 $ wt session add feature/auth
 $ wt session add feature/payments
+$ wt session add feature/review --agent-cmd "aider --fast"
 
 # List workspaces with agent status
 $ wt session ls
@@ -249,6 +252,12 @@ does not cause `wt` to pick up unrelated tmux sessions.
 
 `wt session watch` and `--watch` are currently panes-mode only.
 
+`--agent-cmd` is a one-off override for `session.agent_cmd` and only affects the
+`wt session add` invocation it is passed to. It does not update config, and it
+only applies when creating a new panes-mode window or windows-mode session.
+Re-running `wt session add` against an existing tmux target keeps that target's
+current command.
+
 ### Configuration
 
 Create `~/.wt/config.toml` for global settings or `.wt.toml` in repo root for per-repo settings:
@@ -262,7 +271,7 @@ agent_cmd = "claude"   # command for agent pane/window
 editor_cmd = "nvim"    # command for editor pane/window (when panes=3)
 ```
 
-Precedence: `--mode` / `--panes` flags > `.wt.toml` > `~/.wt/config.toml` > defaults
+Precedence: `--mode` / `--panes` / `--agent-cmd` flags > `.wt.toml` > `~/.wt/config.toml` > defaults
 
 ### Navigation
 

src/config.rs

@@ -66,6 +66,16 @@ impl SessionConfig {
     pub fn session_name_for(&self, worktree: &str) -> String {
         format!("{}{}", self.session_prefix, worktree)
     }
+
+    /// Return a copy of the session config with a one-off agent command
+    /// override applied.
+    pub fn with_agent_cmd_override(&self, agent_cmd_override: Option<&str>) -> Self {
+        let mut config = self.clone();
+        if let Some(agent_cmd) = agent_cmd_override {
+            config.agent_cmd = agent_cmd.to_string();
+        }
+        config
+    }
 }
 
 impl Config {
@@ -212,6 +222,39 @@ panes = 3
         assert_eq!(config.session.editor_cmd, "nvim");
     }
 
+    #[test]
+    fn test_with_agent_cmd_override_uses_override_when_present() {
+        let config = SessionConfig::default();
+
+        let effective = config.with_agent_cmd_override(Some("aider --fast"));
+
+        assert_eq!(effective.agent_cmd, "aider --fast");
+        assert_eq!(effective.editor_cmd, config.editor_cmd);
+        assert_eq!(effective.session_prefix, config.session_prefix);
+    }
+
+    #[test]
+    fn test_with_agent_cmd_override_trims_nothing_and_does_not_mutate_original() {
+        let mut config = SessionConfig::default();
+        config.agent_cmd = "claude --resume".to_string();
+
+        let effective = config.with_agent_cmd_override(Some("aider --fast --model sonnet"));
+
+        assert_eq!(effective.agent_cmd, "aider --fast --model sonnet");
+        assert_eq!(config.agent_cmd, "claude --resume");
+    }
+
+    #[test]
+    fn test_with_agent_cmd_override_preserves_config_when_absent() {
+        let config = SessionConfig::default();
+
+        let effective = config.with_agent_cmd_override(None);
+
+        assert_eq!(effective.agent_cmd, config.agent_cmd);
+        assert_eq!(effective.editor_cmd, config.editor_cmd);
+        assert_eq!(effective.session_prefix, config.session_prefix);
+    }
+
     #[test]
     fn test_default_mode_is_panes() {
         let config = Config::default();
@@ -392,6 +435,65 @@ panes = 3
         assert_eq!(config.session.agent_cmd, "aider");
     }
 
+    #[test]
+    fn test_load_layered_local_agent_cmd_overrides_global_agent_cmd() {
+        use std::io::Write;
+
+        let dir = tempfile::tempdir().unwrap();
+        let global = dir.path().join("global.toml");
+        let local = dir.path().join("local.toml");
+
+        writeln!(
+            std::fs::File::create(&global).unwrap(),
+            "[session]\nagent_cmd = \"claude --resume\"\npanes = 2\n"
+        )
+        .unwrap();
+        writeln!(
+            std::fs::File::create(&local).unwrap(),
+            "[session]\nagent_cmd = \"aider --fast\"\n"
+        )
+        .unwrap();
+
+        let config = Config::load_layered(Some(&global), Some(&local));
+        assert_eq!(config.session.agent_cmd, "aider --fast");
+        assert_eq!(config.session.panes, 2);
+    }
+
+    #[test]
+    fn test_full_precedence_chain_cli_beats_local_beats_global_beats_default() {
+        use std::io::Write;
+
+        let dir = tempfile::tempdir().unwrap();
+        let global = dir.path().join("global.toml");
+        let local = dir.path().join("local.toml");
+
+        writeln!(
+            std::fs::File::create(&global).unwrap(),
+            "[session]\nagent_cmd = \"opencode\"\n"
+        )
+        .unwrap();
+        writeln!(
+            std::fs::File::create(&local).unwrap(),
+            "[session]\nagent_cmd = \"claude --resume\"\n"
+        )
+        .unwrap();
+
+        let loaded = Config::load_layered(Some(&global), Some(&local));
+        assert_eq!(loaded.session.agent_cmd, "claude --resume");
+
+        let with_override = loaded.session.with_agent_cmd_override(Some("aider --fast"));
+        assert_eq!(with_override.agent_cmd, "aider --fast");
+
+        let without_override = loaded.session.with_agent_cmd_override(None);
+        assert_eq!(without_override.agent_cmd, "claude --resume");
+
+        let global_only = Config::load_layered(Some(&global), None);
+        assert_eq!(global_only.session.agent_cmd, "opencode");
+
+        let no_files = Config::load_layered(None, None);
+        assert_eq!(no_files.session.agent_cmd, default_agent_cmd());
+    }
+
     #[test]
     fn test_load_layered_returns_default_when_both_missing() {
         let config = Config::load_layered(None, None);

src/main.rs

@@ -424,3 +424,61 @@ fn cmd_use(config: &RepoConfig, name: Option<String>) -> Result<()> {
     spawn_wt_shell(&wt_info.path, &wt_info.task_id, &wt_info.branch)?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cli_session_add_without_agent_cmd_leaves_override_unset() {
+        let cli = Cli::try_parse_from(["wt", "session", "add", "demo"])
+            .expect("session add should parse without --agent-cmd");
+
+        match cli.command {
+            Commands::Session {
+                action: Some(SessionAction::Add { agent_cmd, .. }),
+                ..
+            } => {
+                assert_eq!(agent_cmd, None);
+            }
+            _ => panic!("expected session add command"),
+        }
+    }
+
+    #[test]
+    fn test_cli_parses_session_add_agent_cmd() {
+        let cli = Cli::try_parse_from([
+            "wt",
+            "session",
+            "--mode",
+            "windows",
+            "add",
+            "demo",
+            "--agent-cmd",
+            "aider --fast",
+        ])
+        .expect("session add should accept --agent-cmd");
+
+        match cli.command {
+            Commands::Session {
+                mode,
+                action:
+                    Some(SessionAction::Add {
+                        name,
+                        base,
+                        panes,
+                        agent_cmd,
+                        watch,
+                    }),
+            } => {
+                assert_eq!(mode, Some(SessionMode::Windows));
+                assert_eq!(name, "demo");
+                assert_eq!(base, "main");
+                assert_eq!(panes, None);
+                assert_eq!(agent_cmd.as_deref(), Some("aider --fast"));
+                assert!(!watch);
+            }
+            _ => panic!("expected session add command"),
+        }
+    }
+}