Addresses #9763 Addresses posit-dev/ark#697 Requires this companion PR in ark: posit-dev/ark#1088 ## Summary Adds infrastructure for R session init hooks that fire after the frontend is fully connected to the runtime. This enables a user or admin to store code in `.Rprofile` that drives the UI or requires two-way communication with the frontend. Two main changes: 1. **`comm_open` data** carries `{ console_width, start_type }` when the UI comm opens. The runtime uses `console_width` immediately (no separate RPC needed). `start_type` is informational/logging. (This is not load-bearing for session init hooks. Rather, it's a little goodie I kept from my second approach to this problem. We had hoped to fire session init hooks during UI comm opening, but it just doesn't work. It's too early. But this does feel like the right way to inform the backend of the initial console width.) 2. **`frontend_ready` RPC** is sent after `comm_open` succeeds. The runtime uses this signal to fire session hooks. This is a separate step from `comm_open` because the hooks may need to make RPCs back to the frontend, which requires the comm to be fully registered first. (This is basically a return to my first approach to the problem. Even more work was required in ark and is described in that PR.) ### Start type mapping `RuntimeStartMode` is an internal Positron enum. `start_type` is the external value sent to the runtime via the `frontend_ready` RPC, which the runtime uses to decide which hooks to fire. | `RuntimeStartMode` (Positron internal) | `start_type` (runtime-facing) | When | |---|---|---| | `Starting` | `"new"` | New runtime session, in a new or existing IDE session | | `Switching` | `"new"` | Notebook switches to a different kernel | | `Restarting` | `"restart"` | Existing runtime session restarted within an IDE session | | `Reconnecting` | `"reconnect"` | Frontend reconnects to an existing runtime session (e.g. window reload, resuming a session on Workbench) | ### Changes - **`ui-backend-openrpc.json`**: Added `frontend_ready` RPC with `start_type` param. Ran codegen (`npx tsx generate-comms.ts ui`), which updated `positronUiComm.ts`, `ui_comm.py`, and `ui_comm.rs` (in ark). - **`languageRuntimeUiClient.ts`**: Added `frontendReady()` wrapper on `UiClientInstance` (the generated method lives on `PositronUiComm` but callers go through `UiClientInstance`). - **`activeRuntimeSession.ts`**: Tracks `startMode` on `ActiveRuntimeSession`. New `getStartType()` maps it to runtime-facing values. `startUiClientImpl()` passes `{ console_width, start_type }` in `comm_open` data (previously `{}`). Sends `frontendReady(startType)` after comm setup completes. - **`runtimeSession.ts`**: Threads `startMode` through `attachToSession()` and updates it when a restart is detected. - **`positron-r/session.ts`**: Removed `setConsoleWidth()` (now handled via `comm_open` data on the ark side). ### Background This enables runtime-side session init hooks, inspired by RStudio's `rstudio.sessionInit`. See the ark companion PR for the runtime-side implementation. Relevant docs re: RStudio: * https://rstudio.github.io/rstudioapi/articles/r-session.html#running-at-startup * https://docs.posit.co/ide/server-pro/admin/rstudio_pro_sessions/session_startup_scripts.html What sorts of things do people do in `rstudio.sessionInit`? Special thanks to @jthomasmock for helping gather this list. It's worth noting that session init hooks are much more relevant in a Workbench/enterprise context than desktop/individual user. * Use rstudioapi to do something that drives the UI, such as `rstudioapi::navigateToFile()`. This has been my main manual test case. However, since it's "fire and forget", it can't be the *only* test case. * Use rstudioapi to trigger two-way communication with the UI, such as `rstudioapi::getActiveProject()`. This turns out to be a very important use case to test. * Emit a welcome message that is correctly formatted for the actual console width (versus a default of 80). r-lib/cli#578 * Display a legal compliance message to users in new sessions. * Reinstall R packages, e.g. via `renv::restore()`, after an OS upgrade. Note that the hook itself does not detect the OS upgrade. But if the upgrade has been detected, the hook gets registered. This example is from Posit Cloud. * Defer package load that was conflicting with other startup events (package installation). This example is from RStudio itself. rstudio/rstudio#2656 * Switch the RStudio theme (light vs. dark) based on the time of day. From rsthemes recommended usage. gadenbuie/rsthemes#8 * Automatically load sparklyr and establish a Spark connection to a YARN cluster. * Append an internal package repository or library path in a way that absolutely can't be clobbered by RStudio itself. ### Release Notes #### New Features - `positron.session_init` and `positron.session_reconnect` are new hooks that are executed in the R session, once R startup is complete and Positron is fully operational and able to handle requests that pertain to the UI, such as rstudioapi calls. This duo is intended to be analogous to RStudio's `rstudio.sessionInit`. A `positron.session_init` hook function should accept a `start_type` parameter, with possible values `"new"` or `"restart"`. A `positron.session_reconnect` hook takes no input. #### Bug Fixes - N/A ### QA Notes Temporarily make this your `.Rprofile` (requires ark built from companion PR) and make sure the current folder has a `DESCRIPTION` file. <details> <summary>Click to expand</summary> ```r message("Plain message, before session init hooks are defined") message("cli thinks the width is ", cli::console_width()) setHook( "positron.session_init", function(start_type) { message( "positron.session_init called with `start_type = '", start_type, "'`" ) message("cli thinks the width is ", cli::console_width()) switch( start_type, new = message("Welcome to Positron ", rstudioapi::getVersion()), restart = message( "Welcome BACK to Positron ", rstudioapi::getVersion() ), message("Unknown start_type: ", start_type) ) open_this <- "DESCRIPTION" if (file.exists(open_this)) { message("Opening '", open_this, "'") rstudioapi::navigateToFile(open_this) } message("Active project: ", rstudioapi::getActiveProject()) }, action = "append" ) setHook( "positron.session_reconnect", function(...) { message("Reconnected to Positron ", rstudioapi::getVersion()) message("Active project: ", rstudioapi::getActiveProject()) message("cli thinks the width is ", cli::console_width()) }, action = "append" ) message("Another plain message, after session init hooks are defined") ``` </details> In each case, `DESCRIPTION` should be opened in the editor via `rstudioapi::navigateToFile()`. Here's what you should see in the Console, up to whatever your console width and active project are. **New session** (`start_type = "new"`): ``` Plain message, before session init hooks are defined cli thinks the width is 80 Another plain message, after session init hooks are defined positron.session_init called with `start_type = 'new'` cli thinks the width is 148 Welcome to Positron 2026.4.0 Opening 'DESCRIPTION' Active project: /Users/jenny/work/readr ``` **Restart R** (`start_type = "restart"`): ``` Plain message, before session init hooks are defined cli thinks the width is 80 Another plain message, after session init hooks are defined positron.session_init called with `start_type = 'restart'` cli thinks the width is 148 Welcome BACK to Positron 2026.4.0 Opening 'DESCRIPTION' Active project: /Users/jenny/work/readr ``` **Reload window** (`start_type = "reconnect"`): Notice that *only* the hook is being run, not the top-level `.Rprofile` statements. ``` Reconnected to Positron 2026.4.0 Active project: /Users/jenny/work/readr cli thinks the width is 148 ``` TODOs: - [x] Why `.Rprofile` messages so red? posit-dev/ark#1101 - [x] Why can't you do `readline()` or `menu()` in a session init hook? posit-dev/ark#1130 - [ ] Consider an E2E test. Open an issue. - [ ] Documentation. Open an issue for this. --------- Signed-off-by: Jennifer (Jenny) Bryan <jenny.f.bryan@gmail.com>

menu() and readline() don't work in positron session init hooks #1130

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`menu()` and `readline()` don't work in positron session init hooks #1130