Every lock of the store goes through Db::conn

Db::conn is documented as the one way to take the lock, yet five production and
test sites reached past it with db.0.lock(): the startup summary, the desktop's
trash sweep and config_get, and tests in sharing and update. All five now call
conn().

DRY pass #2, batch 2, F8 (#5372).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/src-tauri/src/commands/local.rs

@@ -25,7 +25,7 @@ pub fn config_get(db: State<'_, Db>) -> PublicConfig {
     // be enforced. A store error falls back to the default rather than failing the
     // call — the app must still boot.
     let fallback = retention::LOCAL_RETENTION_DAYS;
-    let retention_days = match db.0.lock() {
+    let retention_days = match db.conn() {
         Ok(conn) => state::effective_retention_days(&conn, fallback).unwrap_or(fallback),
         Err(_) => fallback,
     };

desktop/src-tauri/src/lib.rs

@@ -269,7 +269,7 @@ fn paint_window_before_the_webview_does(app: &tauri::App) {
 /// user is present for is one they can see the result of. A failure here is logged and
 /// stepped over — housekeeping must never be the reason the app won't open.
 fn sweep_local_trash(db: &local::Db) {
-    let conn = match db.0.lock() {
+    let conn = match db.conn() {
         Ok(conn) => conn,
         Err(_) => {
             log::warn!("skipping the trash sweep: store lock poisoned");

desktop/src-tauri/src/update.rs

@@ -553,7 +553,7 @@ mod tests {
 
     /// The channel `update_check` would actually use.
     fn effective(db: &Db) -> Channel {
-        let conn = db.0.lock().expect("lock");
+        let conn = db.conn().expect("lock");
         store::pref(&conn, CHANNEL_PREF)
             .expect("read pref")
             .as_deref()
@@ -562,7 +562,7 @@ mod tests {
     }
 
     fn set_channel(db: &Db, channel: Channel) {
-        let conn = db.0.lock().expect("lock");
+        let conn = db.conn().expect("lock");
         store::set_pref(&conn, CHANNEL_PREF, channel.as_str()).expect("set pref");
     }
 
@@ -702,7 +702,7 @@ mod tests {
     }
 
     fn set_server(db: &Db, value: &str) {
-        let conn = db.0.lock().expect("lock");
+        let conn = db.conn().expect("lock");
         store::set_pref(&conn, SERVER_PREF, value).expect("set pref");
     }
 
@@ -780,7 +780,7 @@ mod tests {
         let db = db();
         assert_eq!(token_for(&db, "https://notes.example.com"), Ok(None));
         {
-            let conn = db.0.lock().expect("lock");
+            let conn = db.conn().expect("lock");
             state::set_link(&conn, "https://notes.example.com/", "tok").expect("link");
         }
         assert_eq!(