feat(window-settings): add TitlebarMode enum and titlebar_mode column

Adds a 4-value mode enum (Qbz | System | Plasma | Hidden) to the existing
WindowSettings store, with column migration that infers mode from the
legacy use_system_titlebar flag. Setter is write-through so the legacy
column stays consistent for any remaining readers.

cc

src-tauri/src/config/window_settings.rs

@@ -9,9 +9,44 @@ use serde::{Deserialize, Serialize};
 use std::path::Path;
 use std::sync::{Arc, Mutex};
 
+/// Titlebar rendering mode. Controls which decoration source is active and
+/// how the custom titlebar component renders (or whether it renders at all).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum TitlebarMode {
+    /// Default — full custom titlebar with drag, resize, dblclick, controls.
+    Qbz,
+    /// OS-native chrome (CSD on Wayland, KWin SSD on X11, NSWindow on macOS).
+    System,
+    /// KDE-only — KWin SSD via Xwayland + stripped custom strip below for search+nav.
+    Plasma,
+    /// No titlebar — for tiling WMs (i3/Hyprland/sway/niri).
+    Hidden,
+}
+
+impl TitlebarMode {
+    /// Whether this mode requests OS decorations (decorations=true at window creation).
+    pub fn wants_decorations(self) -> bool {
+        matches!(self, TitlebarMode::System | TitlebarMode::Plasma)
+    }
+
+    /// Whether this mode requires GDK_BACKEND=x11 to coerce SSD on Wayland.
+    pub fn wants_xwayland(self) -> bool {
+        matches!(self, TitlebarMode::Plasma)
+    }
+}
+
+impl Default for TitlebarMode {
+    fn default() -> Self {
+        TitlebarMode::Qbz
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct WindowSettings {
-    /// Use OS native window decorations instead of custom title bar
+    /// Use OS native window decorations (legacy — superseded by `titlebar_mode`).
+    /// Kept as a write-through shadow of `titlebar_mode in {System, Plasma}` for
+    /// any consumers that still read it; will be removed in a follow-up.
     pub use_system_titlebar: bool,
     /// Last saved window width (logical pixels, non-maximized)
     pub window_width: f64,
@@ -23,6 +58,8 @@ pub struct WindowSettings {
     /// Implies building the window transparent on Linux so the corners
     /// can be seen through to the desktop. Requires restart to take effect.
     pub match_system_window_chrome: bool,
+    /// Authoritative titlebar mode (replaces `use_system_titlebar`).
+    pub titlebar_mode: TitlebarMode,
 }
 
 impl Default for WindowSettings {
@@ -33,6 +70,7 @@ impl Default for WindowSettings {
             window_height: 800.0,
             is_maximized: false,
             match_system_window_chrome: false,
+            titlebar_mode: TitlebarMode::Qbz,
         }
     }
 }
@@ -86,6 +124,26 @@ impl WindowSettingsStore {
             [],
         );
 
+        // Add titlebar_mode column. Defaults to NULL so we can detect
+        // pre-existing rows and migrate from use_system_titlebar.
+        let _ = conn.execute(
+            "ALTER TABLE window_settings ADD COLUMN titlebar_mode TEXT",
+            [],
+        );
+
+        // One-time migration: if titlebar_mode is NULL but use_system_titlebar
+        // exists, derive mode. This runs at every open but only does work on
+        // rows where titlebar_mode is still NULL (idempotent).
+        let _ = conn.execute(
+            "UPDATE window_settings
+             SET titlebar_mode = CASE
+                 WHEN use_system_titlebar = 1 THEN 'system'
+                 ELSE 'qbz'
+             END
+             WHERE titlebar_mode IS NULL AND id = 1",
+            [],
+        );
+
         info!("[WindowSettings] Database initialized");
 
         Ok(Self { conn })
@@ -102,11 +160,32 @@ impl WindowSettingsStore {
         Self::open_at(base_dir, "window_settings.db")
     }
 
+    /// Lightweight read-only open for startup (before Tauri state).
+    /// Opens existing DB without creating tables/running migrations.
+    pub fn new_readonly() -> Result<Self, String> {
+        let db_path = dirs::data_dir()
+            .ok_or("Could not determine data directory")?
+            .join("qbz")
+            .join("window_settings.db");
+
+        if !db_path.exists() {
+            return Err("Window settings DB does not exist yet".to_string());
+        }
+
+        let conn = Connection::open_with_flags(
+            &db_path,
+            rusqlite::OpenFlags::SQLITE_OPEN_READ_ONLY | rusqlite::OpenFlags::SQLITE_OPEN_NO_MUTEX,
+        )
+        .map_err(|e| format!("Failed to open window settings database (readonly): {}", e))?;
+
+        Ok(Self { conn })
+    }
+
     pub fn get_settings(&self) -> Result<WindowSettings, String> {
         self.conn
             .query_row(
                 "SELECT use_system_titlebar, window_width, window_height, is_maximized,
-                        match_system_window_chrome
+                        match_system_window_chrome, titlebar_mode
                  FROM window_settings WHERE id = 1",
                 [],
                 |row| {
@@ -115,6 +194,13 @@ impl WindowSettingsStore {
                     let window_height: f64 = row.get(2)?;
                     let is_maximized: i32 = row.get(3)?;
                     let match_chrome: i32 = row.get(4)?;
+                    let mode_str: Option<String> = row.get(5)?;
+                    let titlebar_mode = match mode_str.as_deref() {
+                        Some("system") => TitlebarMode::System,
+                        Some("plasma") => TitlebarMode::Plasma,
+                        Some("hidden") => TitlebarMode::Hidden,
+                        _ => TitlebarMode::Qbz,
+                    };
                     let defaults = WindowSettings::default();
                     let (w, h) = if is_valid_window_size(window_width, window_height) {
                         (window_width, window_height)
@@ -132,6 +218,7 @@ impl WindowSettingsStore {
                         window_height: h,
                         is_maximized: is_maximized != 0,
                         match_system_window_chrome: match_chrome != 0,
+                        titlebar_mode,
                     })
                 },
             )
@@ -158,6 +245,26 @@ impl WindowSettingsStore {
         Ok(())
     }
 
+    pub fn set_titlebar_mode(&self, mode: TitlebarMode) -> Result<(), String> {
+        let mode_str = match mode {
+            TitlebarMode::Qbz => "qbz",
+            TitlebarMode::System => "system",
+            TitlebarMode::Plasma => "plasma",
+            TitlebarMode::Hidden => "hidden",
+        };
+        let use_system = mode.wants_decorations() as i64;
+        self.conn
+            .execute(
+                "UPDATE window_settings
+                 SET titlebar_mode = ?1, use_system_titlebar = ?2
+                 WHERE id = 1",
+                params![mode_str, use_system],
+            )
+            .map_err(|e| format!("Failed to set titlebar_mode: {}", e))?;
+        info!("Window titlebar_mode set to {}", mode_str);
+        Ok(())
+    }
+
     /// Save the non-maximized window dimensions (called on resize while not maximized).
     pub fn set_window_size(&self, width: f64, height: f64) -> Result<(), String> {
         if !is_valid_window_size(width, height) {
@@ -262,6 +369,23 @@ impl WindowSettingsState {
             .ok_or("Window settings store not initialized")?;
         store.set_match_system_window_chrome(value)
     }
+
+    pub fn set_titlebar_mode(&self, mode: TitlebarMode) -> Result<(), String> {
+        let store = self.store.lock().map_err(|e| format!("lock poisoned: {}", e))?;
+        store
+            .as_ref()
+            .ok_or_else(|| "Window settings store not initialized".to_string())?
+            .set_titlebar_mode(mode)
+    }
+
+    pub fn get_titlebar_mode(&self) -> Result<TitlebarMode, String> {
+        let store = self.store.lock().map_err(|e| format!("lock poisoned: {}", e))?;
+        let settings = store
+            .as_ref()
+            .ok_or_else(|| "Window settings store not initialized".to_string())?
+            .get_settings()?;
+        Ok(settings.titlebar_mode)
+    }
 }
 
 /// Check that window dimensions are within a sane range.