feat: add persistent server-client sessions

   Make herdr persistent by default.

   Launching herdr now starts or reattaches to a background session
   server. Clients can detach and reattach while panes and agent
   processes keep running. Session mode now supports multi-client attach,
   auto-detect startup, and a thin-client/headless-server split.

   This also refactors the large app, ui, input, pane, config,
   workspace, and persistence modules into smaller focused submodules,
   while preserving behavior and colocating tests with the code they
   exercise.

   Upgrade notes:
   - persistence mode is now the default
   - in-app quit detaches the current client instead of stopping the server
   - use `herdr server stop` to stop the background session
   - use `--no-session` for the old single-process behavior
   - default socket paths now live under the config directory

1 files changed, 216 insertions, 0 deletions

diff --git a/src/config/model.rs b/src/config/model.rs
new file mode 100644
index 00000000..70eede5a
--- /dev/null
+++ b/src/config/model.rs
@@ -0,0 +1,216 @@
+use serde::Deserialize;
+
+use super::{CommandKeybindConfig, SoundConfig, ThemeConfig, DEFAULT_SCROLLBACK_LIMIT_BYTES};
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct ToastConfig {
+    pub enabled: bool,
+}
+
+#[derive(Debug, Default, Deserialize)]
+#[serde(default)]
+pub struct Config {
+    pub onboarding: Option<bool>,
+    pub theme: ThemeConfig,
+    pub keys: KeysConfig,
+    pub ui: UiConfig,
+    pub advanced: AdvancedConfig,
+}
+
+#[derive(Debug)]
+pub struct LoadedConfig {
+    pub config: Config,
+    pub diagnostics: Vec<String>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(default)]
+pub struct KeysConfig {
+    /// Prefix key to toggle navigate mode (e.g. "ctrl+b", "f12", "esc").
+    pub prefix: String,
+    /// Create a new workspace. Default: "n"
+    pub new_workspace: String,
+    /// Rename the selected workspace. Default: "shift+n"
+    pub rename_workspace: String,
+    /// Close the selected workspace. Default: "shift+d"
+    pub close_workspace: String,
+    /// Optional explicit detach shortcut in server/client mode. Unset by default.
+    pub detach: String,
+    /// Select the previous workspace. Unset by default.
+    pub previous_workspace: String,
+    /// Select the next workspace. Unset by default.
+    pub next_workspace: String,
+    /// Create a new tab in the active workspace. Default: "c"
+    pub new_tab: String,
+    /// Rename the active tab. Unset by default.
+    pub rename_tab: String,
+    /// Select the previous tab. Unset by default.
+    pub previous_tab: String,
+    /// Select the next tab. Unset by default.
+    pub next_tab: String,
+    /// Close the active tab. Unset by default.
+    pub close_tab: String,
+    /// Focus the pane to the left in terminal mode. Unset by default.
+    pub focus_pane_left: String,
+    /// Focus the pane below in terminal mode. Unset by default.
+    pub focus_pane_down: String,
+    /// Focus the pane above in terminal mode. Unset by default.
+    pub focus_pane_up: String,
+    /// Focus the pane to the right in terminal mode. Unset by default.
+    pub focus_pane_right: String,
+    /// Split pane vertically (side by side). Default: "v"
+    pub split_vertical: String,
+    /// Split pane horizontally (stacked). Default: "-"
+    pub split_horizontal: String,
+    /// Close the focused pane. Default: "x"
+    pub close_pane: String,
+    /// Toggle fullscreen for the focused pane. Default: "f"
+    pub fullscreen: String,
+    /// Enter resize mode. Default: "r"
+    pub resize_mode: String,
+    /// Toggle sidebar collapse. Default: "b"
+    pub toggle_sidebar: String,
+    /// Prefix-mode custom command bindings.
+    pub command: Vec<CommandKeybindConfig>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(default)]
+pub struct UiConfig {
+    pub sidebar_width: u16,
+    /// Ask for confirmation before closing a workspace. Default: true.
+    pub confirm_close: bool,
+    /// Accent color for highlights, borders, and navigation UI.
+    /// Accepts hex (#89b4fa), named colors (cyan, blue), or RGB (rgb(137,180,250)).
+    pub accent: String,
+    /// Optional visual toast notifications for background workspace events.
+    pub toast: ToastConfig,
+    /// Play sounds when agents change state in background workspaces.
+    pub sound: SoundConfig,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(default)]
+pub struct AdvancedConfig {
+    /// Allow launching herdr inside an existing herdr pane. Default: false.
+    pub allow_nested: bool,
+    /// Maximum scrollback buffer size in bytes retained per pane terminal. Default: 10000000.
+    #[serde(alias = "scrollback_lines")]
+    pub scrollback_limit_bytes: usize,
+}
+
+impl Default for KeysConfig {
+    fn default() -> Self {
+        Self {
+            prefix: "ctrl+b".into(),
+            new_workspace: "n".into(),
+            rename_workspace: "shift+n".into(),
+            close_workspace: "shift+d".into(),
+            detach: "".into(),
+            previous_workspace: "".into(),
+            next_workspace: "".into(),
+            new_tab: "c".into(),
+            rename_tab: "".into(),
+            previous_tab: "".into(),
+            next_tab: "".into(),
+            close_tab: "".into(),
+            focus_pane_left: "".into(),
+            focus_pane_down: "".into(),
+            focus_pane_up: "".into(),
+            focus_pane_right: "".into(),
+            split_vertical: "v".into(),
+            split_horizontal: "-".into(),
+            close_pane: "x".into(),
+            fullscreen: "f".into(),
+            resize_mode: "r".into(),
+            toggle_sidebar: "b".into(),
+            command: Vec::new(),
+        }
+    }
+}
+
+impl Default for UiConfig {
+    fn default() -> Self {
+        Self {
+            sidebar_width: 26,
+            confirm_close: true,
+            accent: "cyan".into(),
+            toast: ToastConfig::default(),
+            sound: SoundConfig::default(),
+        }
+    }
+}
+
+impl Default for ToastConfig {
+    fn default() -> Self {
+        Self { enabled: false }
+    }
+}
+
+impl Default for AdvancedConfig {
+    fn default() -> Self {
+        Self {
+            allow_nested: false,
+            scrollback_limit_bytes: DEFAULT_SCROLLBACK_LIMIT_BYTES,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn toast_config_parses() {
+        let toml = r#"
+[ui.toast]
+enabled = true
+"#;
+        let config: Config = toml::from_str(toml).unwrap();
+        assert!(config.ui.toast.enabled);
+    }
+
+    #[test]
+    fn missing_onboarding_shows_setup() {
+        let config = Config::default();
+        assert!(config.should_show_onboarding());
+    }
+
+    #[test]
+    fn onboarding_false_skips_setup() {
+        let config: Config = toml::from_str("onboarding = false").unwrap();
+        assert!(!config.should_show_onboarding());
+    }
+
+    #[test]
+    fn advanced_defaults_include_scrollback_limit_bytes() {
+        let config = Config::default();
+        assert_eq!(
+            config.advanced.scrollback_limit_bytes,
+            DEFAULT_SCROLLBACK_LIMIT_BYTES
+        );
+    }
+
+    #[test]
+    fn advanced_config_parses() {
+        let toml = r#"
+[advanced]
+allow_nested = true
+scrollback_limit_bytes = 12345
+"#;
+        let config: Config = toml::from_str(toml).unwrap();
+        assert!(config.advanced.allow_nested);
+        assert_eq!(config.advanced.scrollback_limit_bytes, 12345);
+    }
+
+    #[test]
+    fn advanced_legacy_scrollback_lines_alias_parses() {
+        let toml = r#"
+[advanced]
+scrollback_lines = 12345
+"#;
+        let config: Config = toml::from_str(toml).unwrap();
+        assert_eq!(config.advanced.scrollback_limit_bytes, 12345);
+    }
+}