fix(summer): give delegated commands the terminal and keep their stderr apart

- appStreams hands the app binary summer's own stdout and stderr on a
  terminal, so it asks the production question, prints styled summaries
  and animates its widgets
- off a terminal the binary's stdout goes through summer's Output and its
  stderr to summer's stderr, so --json and -q output carry no log lines
- newAppCmd (unexported) takes the two writers; docs say the streams stay
  apart (CR-03)

cmd/summer/runtime.go

@@ -141,7 +141,22 @@ func runAppBinary(ctx context.Context, argv []string, out bonfire.Output) error
 			return fmt.Errorf("summer: refusing to recurse into %s", bin)
 		}
 	}
-	return runAppCmd(newAppCmd(ctx, bin, appDir, argv, out), argv)
+	stdout, stderr := appStreams(out, bonfire.IsTerminal(out))
+	return runAppCmd(newAppCmd(ctx, bin, appDir, argv, stdout, stderr), argv)
+}
+
+// appStreams picks the app binary's stdout and stderr. On a terminal
+// (terminal is bonfire.IsTerminal(out)) the binary gets summer's own
+// streams, so it sees the terminal: it asks the production question, prints
+// styled summaries and animates its widgets. Otherwise its stdout goes
+// through out (tests and bonfire.Call roots capture it) and its stderr to
+// summer's stderr, so log lines and error blocks never mix into data such
+// as --json output.
+func appStreams(out bonfire.Output, terminal bool) (stdout, stderr io.Writer) {
+	if terminal {
+		return os.Stdout, os.Stderr
+	}
+	return out, os.Stderr
 }
 
 // runAppCmd runs cmd, the app binary started with argv, forwarding SIGINT
@@ -170,15 +185,16 @@ func runAppCmd(cmd *exec.Cmd, argv []string) error {
 // timeout of serve and the workers, so they finish a graceful shutdown.
 const appShutdownGrace = 15 * time.Second
 
-// newAppCmd builds the command that runs the app binary bin with argv in dir.
-// The child inherits summer's stdin, so the hidden password prompts of
-// admin:create and admin:reset-password read from the terminal. Cancelling
-// ctx sends SIGTERM, and the child is killed only after appShutdownGrace.
-func newAppCmd(ctx context.Context, bin, dir string, argv []string, out io.Writer) *exec.Cmd {
+// newAppCmd builds the command that runs the app binary bin with argv in
+// dir, writing to stdout and stderr (see appStreams). The child inherits
+// summer's stdin, so the hidden password prompts of admin:create and
+// admin:reset-password read from the terminal. Cancelling ctx sends
+// SIGTERM, and the child is killed only after appShutdownGrace.
+func newAppCmd(ctx context.Context, bin, dir string, argv []string, stdout, stderr io.Writer) *exec.Cmd {
 	cmd := exec.CommandContext(ctx, bin, argv...)
 	cmd.Dir = dir
-	cmd.Stdout = out
-	cmd.Stderr = out
+	cmd.Stdout = stdout
+	cmd.Stderr = stderr
 	cmd.Stdin = os.Stdin
 	cmd.Env = os.Environ()
 	cmd.Cancel = func() error {

cmd/summer/runtime_test.go

@@ -5,9 +5,11 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"os/signal"
+	"path/filepath"
 	"runtime"
 	"slices"
 	"strings"
@@ -189,7 +191,7 @@ func TestRunChildForwardsSignals(t *testing.T) {
 	for _, sig := range []os.Signal{os.Interrupt, syscall.SIGTERM} {
 		t.Run(sig.String(), func(t *testing.T) {
 			var out syncBuffer
-			cmd := newAppCmd(context.Background(), os.Args[0], ".", helperArgv(), &out)
+			cmd := newAppCmd(context.Background(), os.Args[0], ".", helperArgv(), &out, &out)
 			helperEnv(cmd)
 			sigs := make(chan os.Signal, 1)
 			done := make(chan error, 1)
@@ -218,7 +220,7 @@ func TestNewAppCmdCancelSendsSIGTERM(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	var out syncBuffer
-	cmd := newAppCmd(ctx, os.Args[0], ".", helperArgv(), &out)
+	cmd := newAppCmd(ctx, os.Args[0], ".", helperArgv(), &out, &out)
 	helperEnv(cmd)
 	done := make(chan error, 1)
 	go func() { done <- runChild(cmd, nil) }()
@@ -311,7 +313,8 @@ func exitHelperRunner(t *testing.T, mode string) {
 	t.Helper()
 	prev := appRunner
 	appRunner = func(ctx context.Context, argv []string, out bonfire.Output) error {
-		cmd := newAppCmd(ctx, os.Args[0], ".", []string{"-test.run=^TestExitHelperProcess$"}, out)
+		stdout, stderr := appStreams(out, bonfire.IsTerminal(out))
+		cmd := newAppCmd(ctx, os.Args[0], ".", []string{"-test.run=^TestExitHelperProcess$"}, stdout, stderr)
 		cmd.Env = append(os.Environ(), "SUMMER_EXIT_HELPER="+mode)
 		return runAppCmd(cmd, argv)
 	}
@@ -360,3 +363,53 @@ func TestDelegateExitCodePassthrough(t *testing.T) {
 		}
 	})
 }
+
+// TestDelegateStreams (CR-03): off a terminal the app binary's stdout goes
+// through summer's Output and its stderr to summer's stderr, never into
+// summer's stdout.
+func TestDelegateStreams(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("the fake app binary is a shell script")
+	}
+	app := t.TempDir()
+	if err := os.WriteFile(filepath.Join(app, "summer.yaml"), []byte("module: example.com/acme\nbinary: acme\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.MkdirAll(filepath.Join(app, "bin"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	script := "#!/bin/sh\necho data-line\necho log-line >&2\n"
+	if err := os.WriteFile(filepath.Join(app, "bin", "acme"), []byte(script), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	t.Chdir(app)
+	out, err := runSummer(t, "route:list", "--json")
+	if err != nil {
+		t.Fatalf("route:list: %v\n%s", err, out)
+	}
+	if !strings.Contains(out, "data-line") {
+		t.Errorf("the binary's stdout did not reach summer's Output: %q", out)
+	}
+	if strings.Contains(out, "log-line") {
+		t.Errorf("the binary's stderr landed in summer's stdout: %q", out)
+	}
+}
+
+// TestAppStreams (CR-03): on a terminal the app binary gets summer's own
+// stdout and stderr; off a terminal its stdout goes through the Output and
+// its stderr to summer's stderr.
+func TestAppStreams(t *testing.T) {
+	var buf bytes.Buffer
+	out := bonfire.NewOutput(strings.NewReader(""), &buf, &buf)
+	if bonfire.IsTerminal(out) {
+		t.Fatal("a buffer console reports a terminal")
+	}
+	stdout, stderr := appStreams(out, true)
+	if stdout != os.Stdout || stderr != os.Stderr {
+		t.Errorf("terminal: streams %v, %v; want os.Stdout, os.Stderr", stdout, stderr)
+	}
+	stdout, stderr = appStreams(out, false)
+	if stdout != io.Writer(out) || stderr != os.Stderr {
+		t.Errorf("not a terminal: streams %v, %v; want the Output, os.Stderr", stdout, stderr)
+	}
+}