Drop FlushStaleCells, which no longer has anything to flush

It existed for the incremental re-render: a shorter render left the previous
one's view lines in the tail (deliberately, to avoid a blank frame), and this
cleared them once the new content was fully read. Async renders now build
off-screen and swap in whole, so refreshViewLinesIfNeeded truncates the view
lines to the buffer and no tail can form. All the call at end-of-input still
did was discard every wrapped line and force the whole buffer to be re-wrapped
on the next draw, which is pure work on a large diff.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/commands/oscommands/pty_windows.go

@@ -204,7 +204,8 @@ func (p *winPty) Close() error {
 // slave closes on child exit, but ConPTY keeps the pipe alive until we call
 // ClosePseudoConsole explicitly. Without doing that on child exit, the
 // scanner in pkg/tasks.NewCmdTask would block forever on the next read and
-// the post-content view never gets cleared (FlushStaleCells never fires).
+// the render would never reach its end of input, so the new content would
+// never be swapped in.
 func startWaiter(proc *os.Process, p *winPty) func() error {
 	done := make(chan struct{})
 	var waitErr error

pkg/gocui/view.go

@@ -1248,17 +1248,6 @@ func (v *View) Reset() {
 	v.offscreen = nil
 }
 
-// This is for when we've done a restart for the sake of avoiding a flicker and
-// we've reached the end of the new content to display: we need to clear the remaining
-// content from the previous round. We do this by setting v.viewLines to nil so that
-// we just render the new content from v.buf.lines directly
-func (v *View) FlushStaleCells() {
-	v.writeMutex.Lock()
-	defer v.writeMutex.Unlock()
-
-	v.clearViewLines()
-}
-
 // BeginOffscreenRender starts building a re-render into an off-screen buffer.
 // Until SwapInOffscreenRender promotes it, writes go to that buffer and the
 // displayed buffer — what every reader sees — is left as it was. This is how an

pkg/gui/tasks_adapter.go

@@ -170,8 +170,6 @@ func (gui *Gui) getManager(view *gocui.View) *tasks.ViewBufferManager {
 
 					view.SetOrigin(0, newOriginY)
 				}
-
-				view.FlushStaleCells()
 			},
 			func() {
 				view.SetOrigin(0, 0)