feat(pkg-r): bookmark support

[cpsievert]

Closes #107

This PR adds Shiny bookmarking support to the R package's QueryChat class, bringing it to feature parity with the Python implementation added in #104.

Behavior

When bookmarking is enabled, the following state is preserved across sessions:

• Chat history - Full conversation with the LLM (via shinychat::chat_restore())
• Current SQL query - The active query filtering the data
• Query title - The LLM-generated title for the current query
• Greeting state - Whether the welcome message has been shown (prevents duplicates on restore)

Note

This does raise some questions related to #113 in terms of managing greeting/chat state. I think it'd be better to leave that for a follow up PR where we can address both R and Python at once.

Changes

• mod_server() function - Added enable_bookmarking parameter (default: FALSE)

  • Integrated shinychat::chat_restore() to save/restore chat history
  • Added shiny::onBookmark() handler to save current query, title, and greeting state
  • Added shiny::onRestore() handler to restore saved state
  • Wrapped greeting logic in a reactive observer to prevent duplicate greetings on restore

• QueryChat$server() method - Added enable_bookmarking parameter (default: FALSE)

  • Users can explicitly enable bookmarking in custom apps
  • Passes parameter through to mod_server()

• QueryChat$app_obj() method - Automatically enables bookmarking when appropriate

  • When bookmark_store = "url" (default) or "server", bookmarking is automatically enabled
  • No user action required beyond setting bookmark_store

Usage

Using querychat_app() (automatic)

# Bookmarking enabled by default with URL bookmarking
querychat_app(mtcars, "mtcars")

# Explicitly set bookmark_store
querychat_app(mtcars, "mtcars", bookmark_store = "server")

# Disable bookmarking
querychat_app(mtcars, "mtcars", bookmark_store = "disable")

Using QueryChat$server() in custom apps

qc <- QueryChat$new(mtcars, "mtcars")

ui <- function(request) {
  page_sidebar(
    qc$sidebar(),
    verbatimTextOutput("sql")
  )
}

server <- function(input, output, session) {
  # Explicitly enable bookmarking
  qc_vals <- qc$server(enable_bookmarking = TRUE)

  output$sql <- renderText(qc_vals$sql())
}

shinyApp(ui, server, enableBookmarking = "url")

[cpsievert]

I'm gonna merge this now since this will get R updated with Python and also help unblock #113.

@gadenbuie if you notice anything we should change or improve upon here, I'm happy to address in a follow up.