Create runner pane in temp window

In order to avoid rapid flickering of runner window as it is created
and initialized, create and initialize it in a temporary background
window then bring it in.

doc/vim-tmux-runner.txt

@@ -33,6 +33,7 @@ CONTENTS                                                        *vtr-contents*
         3.9 ................................ |VtrClearOnReattach|
         3.10 ............................... |VtrDetachedName|
         3.11 ............................... |VtrClearSequence|
+        3.12 ............................... |VtrInitTimeout|
 
 ==============================================================================
 ABOUT (1)                                                           *VTR-About*
@@ -344,5 +345,21 @@ insert mode. See the help file, ':help i_Ctrl-v', for more detail.
 
 Default: ""
 
+------------------------------------------------------------------------------
+                                                               *VtrInitTimeout*
+3.12 g:VtrInitTimeout~
+
+Timeout in milliseconds to use when initializing the runner in temporary
+window. This is intended to provide the runner sufficient time to run the
+initializing commands and then be attached to the Vim window.
+
+This timeout is only relevant if VTR is configured to cd to the git root, or
+run an initial command. These can be set through their respective
+configuration options, |g:VtrGitCdUpOnOpen| and |g:VtrInitialCommand|.
+
+    let g:VtrInitTimeout = 100
+
+Default: 500
+
 ==============================================================================
 vim:tw=78:ts=2:sw=2:expandtab:ft=help:norl:

plugin/vim-tmux-runner.vim

@@ -12,16 +12,29 @@ endfunction
 
 function! s:OpenRunnerPane()
     let s:vim_pane = s:ActiveTmuxPaneNumber()
-    let cmd = join(["split-window -p", s:vtr_percentage, "-".s:vtr_orientation])
+    let remote_cmd = join(["new-window", "-d", "-n", g:VtrDetachedName])
-    call s:SendTmuxCommand(cmd)
+    call s:SendTmuxCommand(remote_cmd)
-    let s:runner_pane = s:ActiveTmuxPaneNumber()
+    let [s:detached_window, s:runner_pane] = [s:LastWindowNumber(), 0]
-    call s:FocusVimPane()
     if g:VtrGitCdUpOnOpen
         call s:GitCdUp()
     endif
     if g:VtrInitialCommand != ""
         call s:SendKeys(g:VtrInitialCommand)
     endif
+    if g:VtrInitialCommand || g:VtrGitCdUpOnOpen
+        call s:TimeoutWithProgess()
+    endif
+    call s:ReattachPane()
+endfunction
+
+function! s:TimeoutWithProgess()
+    let timeout_portion = g:VtrInitTimeout / 3
+    echohl String | echon 'Preparing runner.'
+    for time in [1,2,3]
+        execute join(['sleep', timeout_portion.'m'])
+        echon '.'
+    endfor
+    echohl None
 endfunction
 
 function! s:DetachRunnerPane()
@@ -147,7 +160,12 @@ function! s:SendTmuxCommand(command)
 endfunction
 
 function! s:TargetedTmuxCommand(command, target_pane)
-    return a:command . " -t " . a:target_pane
+    if exists("s:detached_window")
+        let target = ':'.s:detached_window.'.'.a:target_pane
+    else
+        let target = a:target_pane
+    endif
+    return join([a:command, " -t ", target])
 endfunction
 
 function! s:_SendKeys(keys)
@@ -325,6 +343,7 @@ function! s:InitializeVariables()
     call s:InitVariable("g:VtrClearOnReorient", 1)
     call s:InitVariable("g:VtrClearOnReattach", 1)
     call s:InitVariable("g:VtrDetachedName", "VTR_Pane")
+    call s:InitVariable("g:VtrInitTimeout", 450)
     call s:InitVariable("g:VtrClearSequence", "")
     let s:vtr_percentage = g:VtrPercentage
     let s:vtr_orientation = g:VtrOrientation