fix: close library upload flow and harden image storage

pigway_frame_flow/storage/database.py

@@ -17,6 +17,7 @@ def encode(value):
 class Database:
     def __init__(self, path):
         self.lock = threading.RLock()
+        self._transaction_depth = 0
         self.conn = sqlite3.connect(path, check_same_thread=False)
         self.conn.row_factory = sqlite3.Row
         self.conn.executescript("""
@@ -68,17 +69,32 @@ class Database:
     @contextmanager
     def transaction(self):
         with self.lock:
-            self.conn.execute("BEGIN IMMEDIATE")
+            nested = self._transaction_depth > 0
+            savepoint = "tx_" + str(self._transaction_depth)
+            self.conn.execute("SAVEPOINT " + savepoint if nested else "BEGIN IMMEDIATE")
+            self._transaction_depth += 1
             try:
                 yield self.conn
-                self.conn.commit()
-            except Exception:
-                self.conn.rollback()
+                if nested:
+                    self.conn.execute("RELEASE SAVEPOINT " + savepoint)
+                else:
+                    self.conn.commit()
+            except BaseException:
+                if nested:
+                    self.conn.execute("ROLLBACK TO SAVEPOINT " + savepoint)
+                    self.conn.execute("RELEASE SAVEPOINT " + savepoint)
+                else:
+                    self.conn.rollback()
                 raise
+            finally:
+                self._transaction_depth -= 1
 
     def execute(self, query, args=()):
-        with self.lock, self.conn:
-            return self.conn.execute(query, args)
+        with self.lock:
+            if self._transaction_depth:
+                return self.conn.execute(query, args)
+            with self.conn:
+                return self.conn.execute(query, args)
 
     def one(self, query, args=()):
         with self.lock: