Handle missing TTY

.gitignore

@@ -3,3 +3,4 @@ dist/
 buildkite.yaml
 .bk.yaml
 build-logs-*
+/bk

internal/agent/stoppable.go

@@ -109,3 +109,11 @@ func (agent StoppableAgent) View() string {
 func (agent StoppableAgent) Errored() bool {
 	return agent.err != nil
 }
+
+func (agent StoppableAgent) Error() error {
+	return agent.err
+}
+
+func (agent StoppableAgent) ID() string {
+	return agent.id
+}

internal/io/confirm.go

@@ -1,10 +1,24 @@
 package io
 
 import (
+	"os"
+
 	"github.com/charmbracelet/huh"
+	"github.com/mattn/go-isatty"
 )
 
 func Confirm(confirmed *bool, title string) error {
+	// If already confirmed via flag, skip the prompt
+	if *confirmed {
+		return nil
+	}
+
+	// If no TTY is available, default to confirmed=true (non-interactive mode)
+	if !isatty.IsTerminal(os.Stdout.Fd()) {
+		*confirmed = true
+		return nil
+	}
+
 	form := huh.NewForm(
 		huh.NewGroup(
 			huh.NewConfirm().

internal/io/confirm_test.go

@@ -0,0 +1,33 @@
+package io
+
+import (
+	"testing"
+)
+
+func TestConfirmWithoutTTY(t *testing.T) {
+	// Test that Confirm works without TTY and defaults to true
+	confirmed := false
+	err := Confirm(&confirmed, "Test confirmation")
+
+	if err != nil {
+		t.Errorf("Confirm should not return error: %v", err)
+	}
+
+	if !confirmed {
+		t.Error("Confirm should default to true when no TTY is available")
+	}
+}
+
+func TestConfirmWithFlag(t *testing.T) {
+	// Test that Confirm respects pre-set flag
+	confirmed := true
+	err := Confirm(&confirmed, "Test confirmation")
+
+	if err != nil {
+		t.Errorf("Confirm should not return error: %v", err)
+	}
+
+	if !confirmed {
+		t.Error("Confirm should respect pre-set flag")
+	}
+}

internal/io/input.go

@@ -19,8 +19,11 @@ func HasDataAvailable(reader io.Reader) bool {
 	case *bufio.Reader:
 		return f.Size() > 0
 	case *strings.Reader:
-		return f.Size() > 0
+		// Check if there are unread bytes remaining
+		return f.Len() > 0
+	default:
+		// For other reader types, we can't easily determine if data is available
+		// This is a conservative approach - assume no data is available
+		return false
 	}
-
-	return false
 }

internal/io/prompt.go

@@ -1,6 +1,12 @@
 package io
 
-import "github.com/charmbracelet/huh"
+import (
+	"errors"
+	"os"
+
+	"github.com/charmbracelet/huh"
+	"github.com/mattn/go-isatty"
+)
 
 const (
 	typeOrganizationMessage = "Pick an organization"
@@ -10,6 +16,11 @@ const (
 // PromptForOne will show the list of options to the user, allowing them to select one to return.
 // It's possible for them to choose none or cancel the selection, resulting in an error.
 func PromptForOne(resource string, options []string) (string, error) {
+	// If no TTY is available, cannot prompt user for selection
+	if !isatty.IsTerminal(os.Stdout.Fd()) {
+		return "", errors.New("cannot prompt for selection: no TTY available (use appropriate flags to specify the selection)")
+	}
+
 	var message string
 	switch resource {
 	case "pipeline":

internal/io/prompt_test.go

@@ -0,0 +1,19 @@
+package io
+
+import (
+	"testing"
+)
+
+func TestPromptForOneWithoutTTY(t *testing.T) {
+	// Test that PromptForOne fails gracefully without TTY
+	_, err := PromptForOne("pipeline", []string{"option1", "option2"})
+
+	if err == nil {
+		t.Error("PromptForOne should return error when no TTY is available")
+	}
+
+	expectedError := "cannot prompt for selection: no TTY available (use appropriate flags to specify the selection)"
+	if err.Error() != expectedError {
+		t.Errorf("Expected error message %q, got %q", expectedError, err.Error())
+	}
+}

pkg/cmd/agent/stop.go

@@ -4,6 +4,8 @@ import (
 	"bufio"
 	"context"
 	"errors"
+	"fmt"
+	"os"
 	"strings"
 	"sync"
 
@@ -12,6 +14,7 @@ import (
 	bk_io "github.com/buildkite/cli/v3/internal/io"
 	"github.com/buildkite/cli/v3/pkg/cmd/factory"
 	tea "github.com/charmbracelet/bubbletea"
+	"github.com/mattn/go-isatty"
 	"github.com/spf13/cobra"
 	"golang.org/x/sync/semaphore"
 )
@@ -53,6 +56,62 @@ func NewCmdAgentStop(f *factory.Factory) *cobra.Command {
 }
 
 func RunStop(cmd *cobra.Command, args []string, opts *AgentStopOptions) error {
+	// Check TTY availability first, before consuming any input
+	if !isatty.IsTerminal(os.Stdout.Fd()) {
+		// Non-TTY mode: run synchronously without interactive UI
+		return runStopNonInteractive(cmd, args, opts)
+	}
+
+	// TTY mode: use interactive UI with Bubble Tea
+	return runStopInteractive(cmd, args, opts)
+}
+
+func runStopNonInteractive(cmd *cobra.Command, args []string, opts *AgentStopOptions) error {
+	var failed []string
+	var agentIDs []string
+
+	// Use the same logic as the original: either stdin OR args
+	if bk_io.HasDataAvailable(cmd.InOrStdin()) {
+		scanner := bufio.NewScanner(cmd.InOrStdin())
+		scanner.Split(bufio.ScanLines)
+		for scanner.Scan() {
+			agentID := scanner.Text()
+			if strings.TrimSpace(agentID) != "" {
+				agentIDs = append(agentIDs, agentID)
+			}
+		}
+		if scanner.Err() != nil {
+			return scanner.Err()
+		}
+	} else if len(args) > 0 {
+		agentIDs = args
+	} else {
+		return errors.New("must supply agents to stop")
+	}
+
+	// Process all agent IDs synchronously
+	for _, agentID := range agentIDs {
+		if strings.TrimSpace(agentID) != "" {
+			org, id := parseAgentArg(agentID, opts.f.Config)
+			_, err := opts.f.RestAPIClient.Agents.Stop(cmd.Context(), org, id, opts.force)
+			if err != nil {
+				failed = append(failed, fmt.Sprintf("Failed to stop agent %s: %v", agentID, err))
+			} else {
+				fmt.Fprintf(cmd.OutOrStdout(), "Stopped agent %s\n", agentID)
+			}
+		}
+	}
+
+	if len(failed) > 0 {
+		for _, failure := range failed {
+			fmt.Fprintf(cmd.OutOrStdout(), "%s\n", failure)
+		}
+		return errors.New("at least one agent failed to stop")
+	}
+	return nil
+}
+
+func runStopInteractive(cmd *cobra.Command, args []string, opts *AgentStopOptions) error {
 	// use a wait group to ensure we exit the program after all agents have finished
 	var wg sync.WaitGroup
 	// this semaphore is used to limit how many concurrent API requests can be sent
@@ -88,6 +147,7 @@ func RunStop(cmd *cobra.Command, args []string, opts *AgentStopOptions) error {
 		return errors.New("must supply agents to stop")
 	}
 
+	// TTY is available, use interactive mode with Bubble Tea
 	bulkAgent := agent.BulkAgent{
 		Agents: agents,
 	}

pkg/cmd/cluster/view.go

@@ -8,7 +8,7 @@ import (
 	"time"
 
 	"github.com/MakeNowJust/heredoc"
-	"github.com/buildkite/cli/v3/internal/io"
+	bk_io "github.com/buildkite/cli/v3/internal/io"
 	"github.com/buildkite/cli/v3/pkg/cmd/factory"
 	"github.com/buildkite/cli/v3/pkg/output"
 	buildkite "github.com/buildkite/go-buildkite/v4"
@@ -113,7 +113,7 @@ func NewCmdClusterView(f *factory.Factory) *cobra.Command {
 			}
 
 			var cluster buildkite.Cluster
-			spinErr := io.SpinWhile("Loading cluster information", func() {
+			spinErr := bk_io.SpinWhile("Loading cluster information", func() {
 				cluster, _, err = f.RestAPIClient.Clusters.Get(cmd.Context(), f.Config.OrganizationSlug(), args[0])
 			})
 			if spinErr != nil {