feat(goose-cli): theme persistence & selection (#1693)

Co-authored-by: Bradley Axen <baxen@squareup.com>

crates/goose-cli/src/session/input.rs

@@ -11,6 +11,7 @@ pub enum InputResult {
     AddExtension(String),
     AddBuiltin(String),
     ToggleTheme,
+    SelectTheme(String),
     Retry,
     ListPrompts(Option<String>),
     PromptCommand(PromptCommandOptions),
@@ -103,6 +104,22 @@ fn handle_slash_command(input: &str) -> Option<InputResult> {
             Some(InputResult::Retry)
         }
         "/t" => Some(InputResult::ToggleTheme),
+        s if s.starts_with("/t ") => {
+            let t = s
+                .strip_prefix("/t ")
+                .unwrap_or_default()
+                .trim()
+                .to_lowercase();
+            if ["light", "dark", "ansi"].contains(&t.as_str()) {
+                Some(InputResult::SelectTheme(t))
+            } else {
+                println!(
+                    "Theme Unavailable: {} Available themes are: light, dark, ansi",
+                    t
+                );
+                Some(InputResult::Retry)
+            }
+        }
         "/prompts" => Some(InputResult::ListPrompts(None)),
         s if s.starts_with(CMD_PROMPTS) => {
             // Parse arguments for /prompts command
@@ -234,6 +251,7 @@ fn print_help() {
         "Available commands:
 /exit or /quit - Exit the session
 /t - Toggle Light/Dark/Ansi theme
+/t <name> - Set theme directly (light, dark, ansi)
 /extension <command> - Add a stdio extension (format: ENV1=val1 command args...)
 /builtin <names> - Add builtin extensions by name (comma-separated)
 /prompts [--extension <name>] - List all available prompts, optionally filtered by extension

crates/goose-cli/src/session/mod.rs

@@ -499,6 +499,28 @@ impl Session {
                     output::set_theme(new_theme);
                     continue;
                 }
+
+                input::InputResult::SelectTheme(theme_name) => {
+                    save_history(&mut editor);
+
+                    let new_theme = match theme_name.as_str() {
+                        "light" => {
+                            println!("Switching to Light theme");
+                            output::Theme::Light
+                        }
+                        "dark" => {
+                            println!("Switching to Dark theme");
+                            output::Theme::Dark
+                        }
+                        "ansi" => {
+                            println!("Switching to Ansi theme");
+                            output::Theme::Ansi
+                        }
+                        _ => output::Theme::Dark,
+                    };
+                    output::set_theme(new_theme);
+                    continue;
+                }
                 input::InputResult::Retry => continue,
                 input::InputResult::ListPrompts(extension) => {
                     save_history(&mut editor);

crates/goose-cli/src/session/output.rs

@@ -67,6 +67,17 @@ pub fn set_theme(theme: Theme) {
         .set_param("GOOSE_CLI_THEME", Value::String(theme.as_config_string()))
         .expect("Failed to set theme");
     CURRENT_THEME.with(|t| *t.borrow_mut() = theme);
+
+    let config = Config::global();
+    let theme_str = match theme {
+        Theme::Light => "light",
+        Theme::Dark => "dark",
+        Theme::Ansi => "ansi",
+    };
+
+    if let Err(e) = config.set_param("GOOSE_CLI_THEME", Value::String(theme_str.to_string())) {
+        eprintln!("Failed to save theme setting to config: {}", e);
+    }
 }
 
 pub fn get_theme() -> Theme {