fix: set inline disposition for renderable blob elements

backend/chainlit/data/sql_alchemy.py

@@ -615,8 +615,23 @@ async def create_element(self, element: "Element"):
         if not element.mime:
             element.mime = "application/octet-stream"
 
+        # Set inline disposition for browser-renderable elements so they display
+        # correctly on chat resume (e.g. PDF in iframe, images in <img> tags).
+        content_disposition = None
+        _RENDERABLE_MIME_PREFIXES = ("image/", "audio/", "video/")
+        _RENDERABLE_MIME_TYPES = ("application/pdf",)
+        if element.mime:
+            if element.mime in _RENDERABLE_MIME_TYPES or element.mime.startswith(
+                _RENDERABLE_MIME_PREFIXES
+            ):
+                content_disposition = "inline"
+
         uploaded_file = await self.storage_provider.upload_file(
-            object_key=file_object_key, data=content, mime=element.mime, overwrite=True
+            object_key=file_object_key,
+            data=content,
+            mime=element.mime,
+            overwrite=True,
+            content_disposition=content_disposition,
         )
         if not uploaded_file:
             raise ValueError(

backend/tests/data/test_sql_alchemy.py

@@ -149,6 +149,68 @@ async def test_create_and_get_element(
     # The 'content' field is not part of the ElementDict, so we remove this assertion
 
 
+async def test_create_element_pdf_inline_disposition(
+    mock_chainlit_context, data_layer: SQLAlchemyDataLayer
+):
+    """PDF elements must get content_disposition=inline for Azure Blob iframe rendering."""
+    async with mock_chainlit_context:
+        from chainlit.element import Pdf
+
+        pdf_element = Pdf(
+            id=str(uuid.uuid4()),
+            name="test.pdf",
+            mime="application/pdf",
+            content=b"%PDF-1.4 fake",
+            for_id="test_step_id",
+        )
+        await data_layer.create_element(pdf_element)
+
+    upload_call = data_layer.storage_provider.upload_file.call_args
+    assert upload_call.kwargs.get("content_disposition") == "inline", (
+        f"Expected content_disposition=inline for PDF, got {upload_call.kwargs}"
+    )
+
+
+async def test_create_element_text_default_disposition(
+    mock_chainlit_context, data_layer: SQLAlchemyDataLayer
+):
+    """Non-renderable elements must keep content_disposition=None (default)."""
+    async with mock_chainlit_context:
+        text_element = Text(
+            id=str(uuid.uuid4()),
+            name="test.txt",
+            mime="text/plain",
+            content="test content",
+            for_id="test_step_id",
+        )
+        await data_layer.create_element(text_element)
+
+    upload_call = data_layer.storage_provider.upload_file.call_args
+    assert upload_call.kwargs.get("content_disposition") is None, (
+        f"Expected content_disposition=None for text/plain, got {upload_call.kwargs}"
+    )
+
+
+async def test_create_element_image_inline_disposition(
+    mock_chainlit_context, data_layer: SQLAlchemyDataLayer
+):
+    """Image elements must get content_disposition=inline."""
+    async with mock_chainlit_context:
+        img_element = Text(
+            id=str(uuid.uuid4()),
+            name="test.png",
+            mime="image/png",
+            content=b"fake png",
+            for_id="test_step_id",
+        )
+        await data_layer.create_element(img_element)
+
+    upload_call = data_layer.storage_provider.upload_file.call_args
+    assert upload_call.kwargs.get("content_disposition") == "inline", (
+        f"Expected content_disposition=inline for image/png, got {upload_call.kwargs}"
+    )
+
+
 async def test_get_current_timestamp(data_layer: SQLAlchemyDataLayer):
     timestamp = await data_layer.get_current_timestamp()
     assert isinstance(timestamp, str)