diff --git a/cardbox/__init__.py b/cardbox/__init__.py
index ad5f45a..14ed9c8 100644
--- a/cardbox/__init__.py
+++ b/cardbox/__init__.py
@@ -1,45 +1,85 @@
-# Expose main data structures from the structures module
-from cardbox.structures import (
-    Card, 
-    CardBox, 
-    TextContent,
-    JsonContent,
-    FieldSchema,
-    ToolContent,
-    ToolCallContent,
-    ToolResultContent,
-    TextFileContent,
-    FileContent,
-    PreviewImage,
-    FieldsSchemaContent,
-    ImageFileContent,
-    PdfFileContent,
-    VideoFileContent,
-    AudioFileContent,
-    MultiFileContent,
-)
-from cardbox.services import CardStore, CardHistory, CardBoxHistory
-from cardbox.engine import ContextEngine
-from cardbox.strategies import (
-	ExtractCodeStrategy,
-	PdfToTextStrategy,
-	Input,
-    InlineTextFileContentStrategy,
-	PdfToTextStrategyInput,
-)
 from cardbox.a2aclient import A2AHelperClient
 from cardbox.adapters import (
     AsyncPostgresStorageAdapter,
     FileStorageAdapter,
-    LocalFileStorageAdapter,
     InMemoryMappingAdapter,
+    LocalFileStorageAdapter,
 )
+from cardbox.config import configure
+from cardbox.engine import ContextEngine
 from cardbox.external import (
+    ExternalObjectError,
+    ExternalObjectNotFoundError,
     ExternalObjectPointer,
     ExternalObjectReader,
-    ExternalObjectError,
     InvalidExternalURIError,
-    ExternalObjectNotFoundError,
     S3ObjectReader,
 )
-from cardbox.config import configure
+from cardbox.services import CardBoxHistory, CardHistory, CardStore
+from cardbox.strategies import (
+    ExtractCodeStrategy,
+    InlineTextFileContentStrategy,
+    Input,
+    PdfToTextStrategy,
+    PdfToTextStrategyInput,
+)
+from cardbox.structures import (
+    AudioFileContent,
+    Card,
+    CardBox,
+    FieldSchema,
+    FieldsSchemaContent,
+    FileContent,
+    ImageFileContent,
+    JsonContent,
+    MultiFileContent,
+    PdfFileContent,
+    PreviewImage,
+    TextContent,
+    TextFileContent,
+    ToolCallContent,
+    ToolContent,
+    ToolResultContent,
+    VideoFileContent,
+)
+
+__all__ = [
+    "A2AHelperClient",
+    "AsyncPostgresStorageAdapter",
+    "AudioFileContent",
+    "Card",
+    "CardBox",
+    "CardBoxHistory",
+    "CardHistory",
+    "CardStore",
+    "ContextEngine",
+    "ExternalObjectError",
+    "ExternalObjectNotFoundError",
+    "ExternalObjectPointer",
+    "ExternalObjectReader",
+    "ExtractCodeStrategy",
+    "FieldSchema",
+    "FieldsSchemaContent",
+    "FileContent",
+    "FileStorageAdapter",
+    "ImageFileContent",
+    "InMemoryMappingAdapter",
+    "InlineTextFileContentStrategy",
+    "Input",
+    "InvalidExternalURIError",
+    "JsonContent",
+    "LocalFileStorageAdapter",
+    "MultiFileContent",
+    "PdfFileContent",
+    "PdfToTextStrategy",
+    "PdfToTextStrategyInput",
+    "PreviewImage",
+    "S3ObjectReader",
+    "TextContent",
+    "TextFileContent",
+    "ToolCallContent",
+    "ToolContent",
+    "ToolResultContent",
+    "VideoFileContent",
+    "configure",
+]
diff --git a/cardbox/adapters/async_storage.py b/cardbox/adapters/async_storage.py
index ec6392e..c760772 100644
--- a/cardbox/adapters/async_storage.py
+++ b/cardbox/adapters/async_storage.py
@@ -348,28 +348,20 @@ async def save_card_box(self, box: "CardBox", tenant_id: str, *, conn: Any = Non
         async with self._connection(conn) as db_conn:
             if box.box_id is None:
                 box.box_id = str(uuid6.uuid7())
-                result = await db_conn.execute(
-                    """
-                    INSERT INTO card_boxes (box_id, tenant_id, card_ids, parent_ids, updated_at)
-                    VALUES (%s, %s, %s, %s, current_timestamp)
-                    RETURNING box_id
-                    """,
-                    (box.box_id, tenant_id, card_ids_json, parent_ids_json),
-                )
-                row = await result.fetchone()
-            else:
-                result = await db_conn.execute(
-                    """
-                    UPDATE card_boxes
-                    SET card_ids = %s, parent_ids = %s, updated_at = current_timestamp
-                    WHERE box_id = %s AND tenant_id = %s
-                    RETURNING box_id
-                    """,
-                    (card_ids_json, parent_ids_json, box.box_id, tenant_id),
-                )
-                row = await result.fetchone()
-                if not row:
-                    raise ValueError(f"card_box with id {box.box_id} not found for tenant {tenant_id}")
+            result = await db_conn.execute(
+                """
+                INSERT INTO card_boxes (box_id, tenant_id, card_ids, parent_ids, updated_at)
+                VALUES (%s, %s, %s, %s, current_timestamp)
+                ON CONFLICT (box_id) DO UPDATE SET
+                    tenant_id = EXCLUDED.tenant_id,
+                    card_ids = EXCLUDED.card_ids,
+                    parent_ids = EXCLUDED.parent_ids,
+                    updated_at = current_timestamp
+                RETURNING box_id
+                """,
+                (box.box_id, tenant_id, card_ids_json, parent_ids_json),
+            )
+            row = await result.fetchone()
 
         box_id = str(row.get("box_id"))
         box.box_id = box_id
@@ -419,6 +411,19 @@ async def load_card_box(self, box_id: str, tenant_id: str, *, conn: Any = None)
         box.card_ids = card_ids
         return box
 
+    async def hydrate_card_box(self, box_id: str, tenant_id: str, *, conn: Any = None) -> Optional[tuple["CardBox", List["Card"]]]:
+        box = await self.load_card_box(box_id, tenant_id, conn=conn)
+        if box is None:
+            return None
+
+        cards: List["Card"] = []
+        for card_id in box.card_ids:
+            card = await self.get_card(card_id, tenant_id, conn=conn)
+            if card is None:
+                return None
+            cards.append(card)
+        return box, cards
+
     async def add_sync_task(self, card_id: str, tenant_id: str, operation: str, *, conn: Any = None) -> None:
         async with self._connection(conn) as db_conn:
             await db_conn.execute(
diff --git a/cardbox/structures.py b/cardbox/structures.py
index 03a8521..46bed36 100644
--- a/cardbox/structures.py
+++ b/cardbox/structures.py
@@ -201,16 +201,28 @@ class TextContent(Content):
     text: str
 
 
+def _is_valid_json_value(value: Any) -> bool:
+    if value is None or isinstance(value, (str, bool, int)):
+        return True
+    if isinstance(value, float):
+        return value == value and value not in (float("inf"), -float("inf"))
+    if isinstance(value, list):
+        return all(_is_valid_json_value(item) for item in value)
+    if isinstance(value, dict):
+        return all(isinstance(key, str) and _is_valid_json_value(item) for key, item in value.items())
+    return False
+
+
 class JsonContent(Content):
     """Represents structured JSON content (dict/list)."""
 
-    data: Union[Dict[str, Any], List[Any]]
+    data: Any
 
     @field_validator("data")
     @classmethod
     def _validate_json_data(cls, value: Any) -> Any:
-        if not isinstance(value, (dict, list)):
-            raise InvalidCardContentError("JsonContent.data must be a dict or list.")
+        if not _is_valid_json_value(value):
+            raise InvalidCardContentError("JsonContent.data must be a valid JSON value.")
         return value