Maintain exec output

exec.go

@@ -114,13 +114,17 @@ func (p *Program) exec(c ExecCommand, fn ExecCallback) {
 
 	// Execute system command.
 	if err := c.Run(); err != nil {
+		p.renderer.resetLinesRendered()
 		_ = p.RestoreTerminal() // also try to restore the terminal.
 		if fn != nil {
 			go p.Send(fn(err))
 		}
 		return
 	}
 
+	// Maintain the existing output from the command
+	p.renderer.resetLinesRendered()
+
 	// Have the program re-capture input.
 	err := p.RestoreTerminal()
 	if fn != nil {

nil_renderer.go

@@ -26,3 +26,4 @@ func (n nilRenderer) setWindowTitle(_ string)    {}
 func (n nilRenderer) reportFocus() bool          { return false }
 func (n nilRenderer) enableReportFocus()         {}
 func (n nilRenderer) disableReportFocus()        {}
+func (n nilRenderer) resetLinesRendered()        {}

renderer.go

@@ -79,6 +79,8 @@ type renderer interface {
 
 	// disableReportFocus stops reporting focus events to the program.
 	disableReportFocus()
+
+	resetLinesRendered()
 }
 
 // repaintMsg forces a full repaint.

standard_renderer.go

@@ -541,6 +541,10 @@ func (r *standardRenderer) clearIgnoredLines() {
 	r.ignoreLines = nil
 }
 
+func (r *standardRenderer) resetLinesRendered() {
+	r.linesRendered = 0
+}
+
 // insertTop effectively scrolls up. It inserts lines at the top of a given
 // area designated to be a scrollable region, pushing everything else down.
 // This is roughly how ncurses does it.