From 56a58d86fae05d85bd09d7b3c9ea1374bd8ef1e9 Mon Sep 17 00:00:00 2001
From: Jason Lunz <znull@github.com>
Date: Tue, 16 Jun 2026 00:44:46 +0200
Subject: [PATCH] Close configured stdout before Output

Release any previously configured stdout stream before replacing it with
the buffer used by Output, preserving ownership of WithStdoutCloser.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 pipe/pipeline_test.go | 17 +++++++++++++++++
 pipe/runner.go        |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/pipe/pipeline_test.go b/pipe/pipeline_test.go
index 7fe7ab5..e003e49 100644
--- a/pipe/pipeline_test.go
+++ b/pipe/pipeline_test.go
@@ -54,6 +54,23 @@ func TestPipelineEmptyOutput(t *testing.T) {
 	}
 }
 
+func TestPipelineOutputClosesConfiguredStdoutCloser(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	stdout := &closeTrackingWriter{}
+	p := pipe.New(
+		pipe.WithStdin(strings.NewReader("hello world\n")),
+		pipe.WithStdoutCloser(stdout),
+	)
+
+	out, err := p.Output(ctx)
+	if assert.NoError(t, err) {
+		assert.Equal(t, "hello world\n", string(out))
+		assert.Equal(t, "", stdout.buf.String())
+		assert.True(t, stdout.closed, "WithStdoutCloser destination should be closed")
+	}
+}
+
 func TestPipelineEmptyWithStdoutCloser(t *testing.T) {
 	t.Parallel()
 	ctx := context.Background()
diff --git a/pipe/runner.go b/pipe/runner.go
index 12e8984..2c44983 100644
--- a/pipe/runner.go
+++ b/pipe/runner.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"fmt"
 )
 
 // Env represents the environment that a pipeline stage should run in.
@@ -152,6 +153,10 @@ func (r *runner) run(ctx context.Context) error {
 func (r *runner) output(ctx context.Context) ([]byte, error) {
 	r.oneUse.assertNotStarted("get output")
 
+	if err := r.stdout.Close(); err != nil {
+		return nil, fmt.Errorf("closing previous stdout: %w", err)
+	}
+
 	var buf bytes.Buffer
 	r.applyOptions(WithStdout(&buf))
 	err := r.run(ctx)