fix: focus source window before dap jumps on event_stopped

When stepping into a library file (e.g., Rust stdlib fmt.rs) or any
file not already open, dap uses its switchbuf logic to decide which
window to load the new source into. The 'uselast' variant targets the
current window if it looks like source (empty buftype or matching
filetype); otherwise it falls back to `winnr('#')`.

Problem: if the user pressed `s` / `d` / `r` while focus was on a
dapui pane (which is common — clicking into Scopes or Watches to
inspect, then stepping), or if the event fires while focus is on our
bar window, dap's current-window check fails and it dumps the new
source into whatever `winnr('#')` resolves to. Combined with
bufferline.nvim's tabline, this produces the chrome-breaking layout
shown in the screenshot.

Fix: register `dap.listeners.before.event_stopped` that shifts focus
to a known source window (via the existing source_window() helper)
BEFORE dap's jump handler runs. Dap's uselast then sees a real source
window as current and lands the new file there. Chrome stays intact.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lua/turbo-debug/mode.lua

@@ -714,6 +714,21 @@ local function ensure_dapui()
   dap.listeners.after.event_terminated["turbo-debug-bar"]   = refresh_bars
   dap.listeners.after.event_exited["turbo-debug-bar"]       = refresh_bars
 
+  -- When a stopped event fires, dap will jump to the source frame using
+  -- its switchbuf logic. `uselast` (the common default) targets the
+  -- CURRENT window — but if focus happens to be on a dapui pane or one
+  -- of our bars, dap falls back to `winnr('#')` which can land anywhere
+  -- (including bufferline's tabline area or a wrong split). By shifting
+  -- focus to a real source window BEFORE dap processes the jump, we
+  -- guarantee new source files (stepped-into library/stdlib files) open
+  -- in the intended source window and the chrome stays intact.
+  dap.listeners.before.event_stopped["turbo-debug-focus-source"] = function()
+    local w = source_window()
+    if w and w ~= vim.api.nvim_get_current_win() then
+      pcall(vim.api.nvim_set_current_win, w)
+    end
+  end
+
   dap.listeners.after.event_stopped["turbo-debug-ip"] = function(session, body)
     vim.defer_fn(function()
       clear_ip()