fix: wait on bash prompt ready marker before sending in keystrokes

internal/screen/screen.go

@@ -32,6 +32,7 @@ type RecordRequest struct {
 type ReplayRequest struct {
 	Cmd       *exec.Cmd
 	Input     []byte
+	InputReady <-chan struct{}
 	OutputLog io.Writer
 }
 
@@ -90,7 +91,7 @@ func Replay(req ReplayRequest) error {
 	defer ptmx.Close()
 
 	outputDone := copyAsync(combineWriters(req.OutputLog), ptmx)
-	inputDone := copyAsync(ptmx, bytes.NewReader(replayInput(req.Input)))
+	inputDone := copyAsyncWhenReady(ptmx, bytes.NewReader(replayInput(req.Input)), req.InputReady)
 
 	waitErr := req.Cmd.Wait()
 	ptmx.Close()
@@ -128,6 +129,18 @@ func copyAsync(dst io.Writer, src io.Reader) <-chan error {
 	return done
 }
 
+func copyAsyncWhenReady(dst io.Writer, src io.Reader, ready <-chan struct{}) <-chan error {
+	done := make(chan error, 1)
+	go func() {
+		if ready != nil {
+			<-ready
+		}
+		_, err := io.Copy(dst, src)
+		done <- normalizeCopyError(err)
+	}()
+	return done
+}
+
 func replayInput(input []byte) []byte {
 	if len(input) > 0 && input[len(input)-1] == terminalEOF {
 		return input

internal/screen/screen_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"os/exec"
 	"testing"
+	"time"
 )
 
 func TestRecordCopiesInputAndOutput(t *testing.T) {
@@ -64,3 +65,31 @@ func TestReplayCapturesOutput(t *testing.T) {
 		t.Fatalf("output log = %q, want marker + line:hello", got)
 	}
 }
+
+func TestReplayWaitsForInputReadySignal(t *testing.T) {
+	cmd := exec.Command("sh", "-c", `IFS= read -r line; printf 'line:%s\n' "$line"`)
+	ready := make(chan struct{})
+
+	var outputLog bytes.Buffer
+	start := time.Now()
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+		close(ready)
+	}()
+
+	if err := Replay(ReplayRequest{
+		Cmd:       cmd,
+		Input:     []byte("hello\n"),
+		InputReady: ready,
+		OutputLog: &outputLog,
+	}); err != nil {
+		t.Fatalf("Replay() error = %v", err)
+	}
+
+	if elapsed := time.Since(start); elapsed < 100*time.Millisecond {
+		t.Fatalf("Replay() elapsed = %v, want >= %v", elapsed, 100*time.Millisecond)
+	}
+	if !bytes.Contains(outputLog.Bytes(), []byte("line:hello")) {
+		t.Fatalf("output log = %q, want line:hello", outputLog.String())
+	}
+}