Feature Request: Option to prevent side panel auto-opening for display="side" elements

[codiak]

Feature Request

Description

When using CustomElement (or other elements) with display="side", the side panel automatically opens every time an element is added to a message. This can be disruptive UX when users have intentionally closed the panel and send another message — the panel reopens on each response.

Current Behavior

sources_element = cl.CustomElement(
    name="Sources",
    props={"items": sources},
    display="side",
)

Every time a message with this element is sent, the side panel opens automatically, even if the user previously closed it.

Desired Behavior

Add an option to control whether the side panel auto-opens, for example:

sources_element = cl.CustomElement(
    name="Sources",
    props={"items": sources},
    display="side",
    auto_expand=False,  # New parameter - default True to preserve current behavior
)

Or a config option in config.toml:

[UI]
auto_expand_side_elements = false

Use Case

In our chat application, we attach sources to every assistant response. Users who prefer to focus on the conversation find it annoying that the sources panel keeps reopening after each message, requiring them to close it repeatedly.

Environment

• Chainlit version: 2.11.1
• Python version: 3.12

Thank you!

[tambagh]

Please don't make this a config.toml option as that would limit per user settings. In addition to the option to auto open, if we can also have an option to set if the element should replace the side panel content (open or not) vs. append to it. It seems with the latest release, side panel elements keep appending to each other which can also be confusing. Ideally we'd have a panel id target as well so we can decide to target a new panel or an existing one to either replace the content or overwrite it.