fix(storage): stop a panic poisoning the connection mutex for the whole session

`RusqliteService` is the path every async database operation in the app
takes, and all seven of its lock sites used a raw `.lock()`. A single
panic while that guard is held poisons the mutex, after which every
database call for the rest of the process returns "poisoned lock" — for
a database-backed app, the entire UI stops working until restart.

`utils::lock` exists to stop exactly this cascade, and `storage::Database`
already used `lock_safe()`. The busiest lock in the app was the one that
did not.

The test poisons the connection the way a panicking row mapper would and
asserts queries still serve.

The same raw-lock pattern remains at ~121 command-layer sites on the
`DatabaseWrapper`/`CredentialsWrapper` mutexes. Those degrade to a failed
command rather than a panic, and converting them is a mechanical sweep
better reviewed on its own.

src-tauri/src/storage/db_service.rs

@@ -7,6 +7,7 @@
 //! - Test with different database backends
 //! - Migrate to other database systems in the future
 
+use crate::utils::lock::MutexSafe;
 use async_trait::async_trait;
 use rusqlite::{params_from_iter, Connection, Result as SqliteResult, Row};
 use std::sync::{Arc, Mutex};
@@ -128,9 +129,10 @@ impl DatabaseService for RusqliteService {
     async fn execute(&self, query: Query) -> DbResult<usize> {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             execute_query(&conn, query)
         })
         .await
@@ -141,9 +143,10 @@ impl DatabaseService for RusqliteService {
         let conn = Arc::clone(&self.conn);
         let sql = sql.to_string();
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             conn.execute_batch(&sql)
                 .map_err(|e| format!("Execute batch failed: {}", e))
         })
@@ -158,9 +161,10 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             query_one(&conn, query, mapper)
         })
         .await
@@ -174,9 +178,10 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             query_optional(&conn, query, mapper)
         })
         .await
@@ -190,9 +195,10 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             query_many(&conn, query, mapper)
         })
         .await
@@ -206,9 +212,10 @@ impl DatabaseService for RusqliteService {
     {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
 
             conn.execute("BEGIN TRANSACTION", [])
                 .map_err(|e| format!("Failed to begin transaction: {}", e))?;
@@ -236,9 +243,10 @@ impl DatabaseService for RusqliteService {
     async fn last_insert_rowid(&self) -> DbResult<i64> {
         let conn = Arc::clone(&self.conn);
         tokio::task::spawn_blocking(move || {
-            let conn = conn
+            // `lock_safe`, not `lock`: this is the busiest lock in the app and a
-                .lock()
+            // panic under the guard would otherwise poison it, failing every
-                .map_err(|e| format!("Failed to lock connection: {}", e))?;
+            // later query with "poisoned lock" until the process restarts.
+            let conn = conn.lock_safe();
             Ok(conn.last_insert_rowid())
         })
         .await
@@ -410,4 +418,48 @@ mod tests {
         let count: i32 = service.query_one(query, |row| row.get(0)).await.unwrap();
         assert_eq!(count, 2);
     }
+    /// A panic while the connection guard is held must not brick every later
+    /// query.
+    ///
+    /// This is the single busiest lock in the app — every async DB operation
+    /// goes through it. With a raw `.lock()`, one panic under the guard poisons
+    /// the mutex and every subsequent call returns "poisoned lock" until the
+    /// process restarts, which for a database-backed app means the whole UI
+    /// stops working. `utils::lock` exists precisely to stop that cascade, and
+    /// `storage::Database` already used it; this path did not.
+    ///
+    /// TRACES: UR-002 | DR-012 | UT-014
+    #[tokio::test]
+    async fn a_poisoned_connection_still_serves_queries() {
+        let conn = Arc::new(Mutex::new(Connection::open_in_memory().unwrap()));
+        {
+            let c = conn.lock_safe();
+            c.execute_batch("CREATE TABLE test (id INTEGER PRIMARY KEY);")
+                .unwrap();
+        }
+
+        // Poison the mutex the way a panicking row mapper would.
+        let poisoner = Arc::clone(&conn);
+        let hook = std::panic::take_hook();
+        std::panic::set_hook(Box::new(|_| {}));
+        let _ = std::thread::spawn(move || {
+            let _guard = poisoner.lock().unwrap();
+            panic!("a row mapper blew up while holding the connection");
+        })
+        .join();
+        std::panic::set_hook(hook);
+        assert!(conn.lock().is_err(), "the mutex should now be poisoned");
+
+        // Every operation must still work.
+        let service = RusqliteService::new(Arc::clone(&conn));
+        service
+            .execute(Query::new("INSERT INTO test (id) VALUES (1)"))
+            .await
+            .expect("execute must survive a poisoned connection");
+        let count: i32 = service
+            .query_one(Query::new("SELECT COUNT(*) FROM test"), |row| row.get(0))
+            .await
+            .expect("query_one must survive a poisoned connection");
+        assert_eq!(count, 1);
+    }
 }