fix(markdown-stream): Scroll to bottom when tool request/results finish rendering

[gadenbuie]

Scrolling to the bottom of the chat stream can be broken (or just generally wonky) when there are many tool requests/results in a message.

This happens generally because the scroll-to-bottom logic runs just after rendering the message content, at which point the tool request/results are still empty containers and haven't yet been rendered by lit, so the scrolling isn't quite in line with the bottom of the container, or can drift.

The fix in this PR is to emit a shiny-chat-maybe-scroll-to-bottom event when the request/result is firstUpdated(), i.e. when it is rendered in the DOM, which then calls into the same scroll to bottom logic that is used when the chat message is updated.

Example

Here's a small example app I've been using (the weather tool). Make the window height small and ask a question that leads to checking the weather in a few cities at once.

Example app

library(shiny)
library(bslib)
library(ellmer)
pkgload::load_all(here::here("pkg-r"))

get_weather_forecast <- tool(
  function(lat, lon, location_name) {
    lat <- unlist(lat)
    lon <- unlist(lon)
    location_name <- unlist(location_name)

    forecast <- weathR::point_tomorrow(lat, lon, short = FALSE)

    icon <- if (any(forecast$temp > 70)) {
      bsicons::bs_icon("sun-fill")
    } else if (any(forecast$temp < 45)) {
      bsicons::bs_icon("snow")
    } else {
      bsicons::bs_icon("cloud-sun-fill")
    }

    ContentToolResult(
      forecast,
      extra = list(
        display = list(
          title = paste("Weather Forecast for", location_name),
          icon = icon
        )
      )
    )
  },
  name = "get_weather_forecast",
  description = "Get the weather forecast for a location.",
  arguments = list(
    lat = type_number("Latitude"),
    lon = type_number("Longitude"),
    location_name = type_string("Name of the location for display to the user")
  ),
  annotations = tool_annotations(
    title = "Weather Forecast",
    icon = bsicons::bs_icon("cloud-sun")
  )
)

create_chat <- function() {
  chat <- chat_ollama(model = "granite4:tiny-h")
  chat$register_tool(get_weather_forecast)
  chat
}

ui <- page_fillable(
  card(
    chat_mod_ui("chat")
  )
)

server <- function(input, output, session) {
  chat_mod_server("chat", create_chat())
}

shinyApp(ui, server)

[cpsievert]

Great, thanks!