[Bug]: Incorrect Error Message for Custom Normalizer Registration

[JamesHWade]

Component

UI (ui.*)

Severity

P2 - Medium (workaround exists)

Shiny Version

1.3.1

Python Version

3.11

Minimal Reproducible Example

from shiny import App, ui
from typing import Any

# Create a custom message type that won't be recognized by any normalizer
class CustomMessage:
    def __init__(self, content):
        self.content = content

app_ui = ui.page_fillable(
    ui.panel_title("Custom Normalizer Example"),
    ui.chat_ui("chat"),
    fillable_mobile=True,
)

def server(input, output, session):
    chat = ui.Chat(id="chat")

    @chat.on_user_submit
    async def _():
        # This will trigger the error with incorrect guidance
        custom_msg = CustomMessage("Hello")
        await chat.append_message(custom_msg)  # Will raise error with incorrect guidance

app = App(app_ui, server)

Behavior

Current: When a user tries to use a message type that doesn't have a registered normalizer, the error message suggests registering a custom normalizer via shiny.ui._chat_types.registry.register(), which doesn't exist.

Expected: The error message should direct users to the correct path: shiny.ui._chat_normalize.message_normalizer_registry.register().

Error Messages (if any)

ValueError: Could not find a normalizer for message of type <class '__main__.CustomMessage'>: <__main__.CustomMessage object at 0x7f8c1d3e5f90>. 
Consider registering a custom normalizer via shiny.ui._chat_types.registry.register()

Environment

MacOS