diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 29763c6..06265f2 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -1,3 +1,5 @@
+pub mod prefs;
+pub mod recents;
 pub mod state;
 pub mod utils;
 
diff --git a/src-tauri/src/prefs.rs b/src-tauri/src/prefs.rs
new file mode 100644
index 0000000..2c55fa6
--- /dev/null
+++ b/src-tauri/src/prefs.rs
@@ -0,0 +1,441 @@
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use std::path::Path;
+use std::time::SystemTime;
+
+use crate::state::{atomic_write_json, load_json_with_fallbacks, BACKUP_COUNT};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct WindowState {
+    pub width: i32,
+    pub height: i32,
+    pub x: Option<i32>,
+    pub y: Option<i32>,
+}
+
+impl Default for WindowState {
+    fn default() -> Self {
+        Self {
+            width: 1320,
+            height: 860,
+            x: None,
+            y: None,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Prefs {
+    #[serde(default = "default_version")]
+    pub version: u32,
+    #[serde(default = "default_ui_zoom")]
+    pub ui_zoom: f64,
+    #[serde(default = "default_split_ratio")]
+    pub split_ratio: f64,
+    #[serde(default = "default_dock_ratio")]
+    pub dock_ratio: f64,
+    #[serde(default)]
+    pub always_on_top: bool,
+    #[serde(default)]
+    pub window: WindowState,
+    #[serde(default)]
+    pub last_folder_path: Option<String>,
+    #[serde(default)]
+    pub last_library_id: Option<String>,
+    #[serde(default)]
+    pub updated_at: u64,
+}
+
+fn default_version() -> u32 {
+    19
+}
+fn default_ui_zoom() -> f64 {
+    1.0
+}
+fn default_split_ratio() -> f64 {
+    0.62
+}
+fn default_dock_ratio() -> f64 {
+    0.62
+}
+
+impl Default for Prefs {
+    fn default() -> Self {
+        Self {
+            version: 19,
+            ui_zoom: 1.0,
+            split_ratio: 0.62,
+            dock_ratio: 0.62,
+            always_on_top: false,
+            window: WindowState::default(),
+            last_folder_path: None,
+            last_library_id: None,
+            updated_at: 0,
+        }
+    }
+}
+
+impl Prefs {
+    /// Load preferences from `{state_dir}/prefs.json`, merging with defaults.
+    ///
+    /// Window fields are merged individually so that a saved file with only
+    /// `{"window": {"width": 800}}` keeps the default height, x, and y.
+    pub fn load(state_dir: &Path) -> Prefs {
+        let path = state_dir.join("prefs.json");
+        let loaded = load_json_with_fallbacks(&path, BACKUP_COUNT);
+
+        let raw = match loaded {
+            Some(v) => v,
+            None => return Prefs::default(),
+        };
+
+        let raw_obj = match raw.as_object() {
+            Some(obj) => obj,
+            None => return Prefs::default(),
+        };
+
+        // Start with defaults
+        let mut prefs = Prefs::default();
+
+        // Merge window fields individually if present
+        if let Some(Value::Object(win_obj)) = raw_obj.get("window") {
+            if let Some(Value::Number(n)) = win_obj.get("width") {
+                if let Some(v) = n.as_i64() {
+                    prefs.window.width = v as i32;
+                }
+            }
+            if let Some(Value::Number(n)) = win_obj.get("height") {
+                if let Some(v) = n.as_i64() {
+                    prefs.window.height = v as i32;
+                }
+            }
+            if let Some(val) = win_obj.get("x") {
+                prefs.window.x = val.as_i64().map(|v| v as i32);
+            }
+            if let Some(val) = win_obj.get("y") {
+                prefs.window.y = val.as_i64().map(|v| v as i32);
+            }
+        }
+
+        // Merge all other top-level keys
+        if let Some(Value::Number(n)) = raw_obj.get("version") {
+            if let Some(v) = n.as_u64() {
+                prefs.version = v as u32;
+            }
+        }
+        if let Some(Value::Number(n)) = raw_obj.get("ui_zoom") {
+            if let Some(v) = n.as_f64() {
+                prefs.ui_zoom = v;
+            }
+        }
+        if let Some(Value::Number(n)) = raw_obj.get("split_ratio") {
+            if let Some(v) = n.as_f64() {
+                prefs.split_ratio = v;
+            }
+        }
+        if let Some(Value::Number(n)) = raw_obj.get("dock_ratio") {
+            if let Some(v) = n.as_f64() {
+                prefs.dock_ratio = v;
+            }
+        }
+        if let Some(Value::Bool(b)) = raw_obj.get("always_on_top") {
+            prefs.always_on_top = *b;
+        }
+        if let Some(val) = raw_obj.get("last_folder_path") {
+            prefs.last_folder_path = val.as_str().map(|s| s.to_string());
+        }
+        if let Some(val) = raw_obj.get("last_library_id") {
+            prefs.last_library_id = val.as_str().map(|s| s.to_string());
+        }
+        if let Some(Value::Number(n)) = raw_obj.get("updated_at") {
+            if let Some(v) = n.as_u64() {
+                prefs.updated_at = v;
+            }
+        }
+
+        prefs
+    }
+
+    /// Save preferences to `{state_dir}/prefs.json`.
+    pub fn save(&self, state_dir: &Path) {
+        let path = state_dir.join("prefs.json");
+        let value = serde_json::to_value(self).expect("failed to serialize Prefs");
+        atomic_write_json(&path, &value, BACKUP_COUNT);
+    }
+
+    /// Apply a partial JSON update, merge window fields individually, set
+    /// `updated_at` to the current unix timestamp, and save.
+    pub fn update(&mut self, patch: &Value, state_dir: &Path) {
+        if let Some(obj) = patch.as_object() {
+            // Merge window fields individually
+            if let Some(Value::Object(win_obj)) = obj.get("window") {
+                if let Some(Value::Number(n)) = win_obj.get("width") {
+                    if let Some(v) = n.as_i64() {
+                        self.window.width = v as i32;
+                    }
+                }
+                if let Some(Value::Number(n)) = win_obj.get("height") {
+                    if let Some(v) = n.as_i64() {
+                        self.window.height = v as i32;
+                    }
+                }
+                if let Some(val) = win_obj.get("x") {
+                    self.window.x = val.as_i64().map(|v| v as i32);
+                }
+                if let Some(val) = win_obj.get("y") {
+                    self.window.y = val.as_i64().map(|v| v as i32);
+                }
+            }
+
+            // Apply other top-level keys
+            if let Some(Value::Number(n)) = obj.get("version") {
+                if let Some(v) = n.as_u64() {
+                    self.version = v as u32;
+                }
+            }
+            if let Some(Value::Number(n)) = obj.get("ui_zoom") {
+                if let Some(v) = n.as_f64() {
+                    self.ui_zoom = v;
+                }
+            }
+            if let Some(Value::Number(n)) = obj.get("split_ratio") {
+                if let Some(v) = n.as_f64() {
+                    self.split_ratio = v;
+                }
+            }
+            if let Some(Value::Number(n)) = obj.get("dock_ratio") {
+                if let Some(v) = n.as_f64() {
+                    self.dock_ratio = v;
+                }
+            }
+            if let Some(Value::Bool(b)) = obj.get("always_on_top") {
+                self.always_on_top = *b;
+            }
+            if let Some(val) = obj.get("last_folder_path") {
+                self.last_folder_path = val.as_str().map(|s| s.to_string());
+            }
+            if let Some(val) = obj.get("last_library_id") {
+                self.last_library_id = val.as_str().map(|s| s.to_string());
+            }
+
+            // Set updated_at to current unix timestamp
+            self.updated_at = SystemTime::now()
+                .duration_since(SystemTime::UNIX_EPOCH)
+                .unwrap_or_default()
+                .as_secs();
+
+            self.save(state_dir);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+    use tempfile::TempDir;
+
+    #[test]
+    fn test_default_prefs() {
+        let prefs = Prefs::default();
+        assert_eq!(prefs.version, 19);
+        assert_eq!(prefs.ui_zoom, 1.0);
+        assert_eq!(prefs.split_ratio, 0.62);
+        assert_eq!(prefs.dock_ratio, 0.62);
+        assert!(!prefs.always_on_top);
+        assert_eq!(prefs.window.width, 1320);
+        assert_eq!(prefs.window.height, 860);
+        assert_eq!(prefs.window.x, None);
+        assert_eq!(prefs.window.y, None);
+        assert_eq!(prefs.last_folder_path, None);
+        assert_eq!(prefs.last_library_id, None);
+        assert_eq!(prefs.updated_at, 0);
+    }
+
+    #[test]
+    fn test_default_window_state() {
+        let ws = WindowState::default();
+        assert_eq!(ws.width, 1320);
+        assert_eq!(ws.height, 860);
+        assert_eq!(ws.x, None);
+        assert_eq!(ws.y, None);
+    }
+
+    #[test]
+    fn test_save_and_load_round_trip() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+        prefs.ui_zoom = 1.5;
+        prefs.split_ratio = 0.75;
+        prefs.always_on_top = true;
+        prefs.window.width = 1920;
+        prefs.window.height = 1080;
+        prefs.window.x = Some(100);
+        prefs.window.y = Some(200);
+        prefs.last_folder_path = Some("/my/folder".to_string());
+        prefs.last_library_id = Some("lib-abc".to_string());
+        prefs.updated_at = 1234567890;
+
+        prefs.save(dir.path());
+
+        let loaded = Prefs::load(dir.path());
+        assert_eq!(loaded.version, 19);
+        assert_eq!(loaded.ui_zoom, 1.5);
+        assert_eq!(loaded.split_ratio, 0.75);
+        assert_eq!(loaded.dock_ratio, 0.62);
+        assert!(loaded.always_on_top);
+        assert_eq!(loaded.window.width, 1920);
+        assert_eq!(loaded.window.height, 1080);
+        assert_eq!(loaded.window.x, Some(100));
+        assert_eq!(loaded.window.y, Some(200));
+        assert_eq!(loaded.last_folder_path, Some("/my/folder".to_string()));
+        assert_eq!(loaded.last_library_id, Some("lib-abc".to_string()));
+        assert_eq!(loaded.updated_at, 1234567890);
+    }
+
+    #[test]
+    fn test_load_nonexistent_returns_defaults() {
+        let dir = TempDir::new().unwrap();
+        let prefs = Prefs::load(dir.path());
+        assert_eq!(prefs.version, 19);
+        assert_eq!(prefs.ui_zoom, 1.0);
+        assert_eq!(prefs.window.width, 1320);
+    }
+
+    #[test]
+    fn test_partial_update() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+
+        let patch = json!({
+            "ui_zoom": 2.0,
+            "always_on_top": true
+        });
+        prefs.update(&patch, dir.path());
+
+        assert_eq!(prefs.ui_zoom, 2.0);
+        assert!(prefs.always_on_top);
+        // Unchanged fields stay at defaults
+        assert_eq!(prefs.split_ratio, 0.62);
+        assert_eq!(prefs.dock_ratio, 0.62);
+        assert_eq!(prefs.window.width, 1320);
+        // updated_at should have been set
+        assert!(prefs.updated_at > 0);
+    }
+
+    #[test]
+    fn test_update_saves_to_disk() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+
+        let patch = json!({"ui_zoom": 3.0});
+        prefs.update(&patch, dir.path());
+
+        let loaded = Prefs::load(dir.path());
+        assert_eq!(loaded.ui_zoom, 3.0);
+    }
+
+    #[test]
+    fn test_window_merge_on_load() {
+        let dir = TempDir::new().unwrap();
+        // Write a JSON file with only partial window data
+        let partial = json!({
+            "window": {"width": 800}
+        });
+        let path = dir.path().join("prefs.json");
+        atomic_write_json(&path, &partial, BACKUP_COUNT);
+
+        let prefs = Prefs::load(dir.path());
+        // Width should be overridden
+        assert_eq!(prefs.window.width, 800);
+        // Height should remain at default
+        assert_eq!(prefs.window.height, 860);
+        // x, y should remain None (defaults)
+        assert_eq!(prefs.window.x, None);
+        assert_eq!(prefs.window.y, None);
+    }
+
+    #[test]
+    fn test_window_merge_on_update() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+        prefs.window.width = 1000;
+        prefs.window.height = 700;
+        prefs.window.x = Some(50);
+        prefs.window.y = Some(60);
+
+        // Patch only width — height, x, y should remain
+        let patch = json!({
+            "window": {"width": 1600}
+        });
+        prefs.update(&patch, dir.path());
+
+        assert_eq!(prefs.window.width, 1600);
+        assert_eq!(prefs.window.height, 700);
+        assert_eq!(prefs.window.x, Some(50));
+        assert_eq!(prefs.window.y, Some(60));
+    }
+
+    #[test]
+    fn test_window_merge_with_position() {
+        let dir = TempDir::new().unwrap();
+        // Saved file has window with x/y set
+        let saved = json!({
+            "version": 19,
+            "window": {"width": 1320, "height": 860, "x": 150, "y": 250}
+        });
+        let path = dir.path().join("prefs.json");
+        atomic_write_json(&path, &saved, BACKUP_COUNT);
+
+        let prefs = Prefs::load(dir.path());
+        assert_eq!(prefs.window.x, Some(150));
+        assert_eq!(prefs.window.y, Some(250));
+    }
+
+    #[test]
+    fn test_load_with_missing_fields_uses_defaults() {
+        let dir = TempDir::new().unwrap();
+        // Write a JSON with only version — everything else should be defaults
+        let partial = json!({"version": 20});
+        let path = dir.path().join("prefs.json");
+        atomic_write_json(&path, &partial, BACKUP_COUNT);
+
+        let prefs = Prefs::load(dir.path());
+        assert_eq!(prefs.version, 20);
+        assert_eq!(prefs.ui_zoom, 1.0);
+        assert_eq!(prefs.split_ratio, 0.62);
+        assert_eq!(prefs.window.width, 1320);
+        assert_eq!(prefs.window.height, 860);
+        assert_eq!(prefs.last_folder_path, None);
+    }
+
+    #[test]
+    fn test_update_with_non_object_is_noop() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+        let original_zoom = prefs.ui_zoom;
+
+        prefs.update(&json!("not an object"), dir.path());
+
+        // Nothing should have changed
+        assert_eq!(prefs.ui_zoom, original_zoom);
+        assert_eq!(prefs.updated_at, 0);
+    }
+
+    #[test]
+    fn test_window_null_xy_in_update() {
+        let dir = TempDir::new().unwrap();
+        let mut prefs = Prefs::default();
+        prefs.window.x = Some(100);
+        prefs.window.y = Some(200);
+
+        // Setting x/y to null should clear them
+        let patch = json!({
+            "window": {"x": null, "y": null}
+        });
+        prefs.update(&patch, dir.path());
+
+        assert_eq!(prefs.window.x, None);
+        assert_eq!(prefs.window.y, None);
+    }
+}