feat(01-02): add CLI display and main.go for vmux list

- DisplaySessions: colored output with state, cwd, branch, preview
- display_test.go: 5 tests covering color, noColor, empty, worktree, noBranch
- main.go: full pipeline FindClaudeProcesses -> FindSession -> DetectState -> Display
- Supports --no-color flag and NO_COLOR env var
- resolveWorktree via git rev-parse --show-toplevel

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

display.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+const (
+	colorReset  = "\033[0m"
+	colorGreen  = "\033[32m"
+	colorYellow = "\033[33m"
+	colorRed    = "\033[31m"
+	colorGray   = "\033[90m"
+	colorBold   = "\033[1m"
+)
+
+// DisplaySessions writes a formatted list of sessions to w.
+func DisplaySessions(w io.Writer, sessions []Session, noColor bool) {
+	if len(sessions) == 0 {
+		fmt.Fprintln(w, "No active Claude Code sessions found.")
+		return
+	}
+
+	for i, s := range sessions {
+		if i > 0 {
+			fmt.Fprintln(w)
+		}
+
+		stateLabel := stateColor(s.State, noColor) + s.State.String() + resetIfColor(noColor)
+
+		branch := ""
+		if s.GitBranch != "" {
+			branch = " (" + s.GitBranch + ")"
+		}
+
+		worktreeInfo := ""
+		if s.Worktree != "" && s.Worktree != s.CwdPath {
+			worktreeInfo = " [worktree: " + s.Worktree + "]"
+		}
+
+		fmt.Fprintf(w, "[%s] %s%s%s\n", stateLabel, s.CwdPath, branch, worktreeInfo)
+
+		if s.Preview != "" {
+			lines := strings.Split(s.Preview, "\n")
+			for _, line := range lines {
+				fmt.Fprintf(w, "         %s\n", line)
+			}
+		}
+	}
+}
+
+func stateColor(state SessionState, noColor bool) string {
+	if noColor {
+		return ""
+	}
+	switch state {
+	case Working:
+		return colorGreen
+	case NeedsInput:
+		return colorYellow
+	case Idle:
+		return colorGray
+	default:
+		return colorGray
+	}
+}
+
+func resetIfColor(noColor bool) string {
+	if noColor {
+		return ""
+	}
+	return colorReset
+}

display_test.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestDisplaySessions_WithSessions(t *testing.T) {
+	sessions := []Session{
+		{
+			Process:   Process{PID: 100, Cwd: "/home/user/project-a"},
+			State:     Working,
+			CwdPath:   "/home/user/project-a",
+			GitBranch: "feat-login",
+			Preview:   "Implementing auth...",
+		},
+		{
+			Process:   Process{PID: 200, Cwd: "/home/user/project-b"},
+			State:     NeedsInput,
+			CwdPath:   "/home/user/project-b",
+			GitBranch: "main",
+			Preview:   "What should I do next?",
+		},
+	}
+
+	var buf bytes.Buffer
+	DisplaySessions(&buf, sessions, false)
+	output := buf.String()
+
+	for _, want := range []string{
+		"/home/user/project-a",
+		"feat-login",
+		"Working",
+		"Implementing auth...",
+		"/home/user/project-b",
+		"main",
+		"Needs Input",
+		"What should I do next?",
+	} {
+		if !strings.Contains(output, want) {
+			t.Errorf("output missing %q", want)
+		}
+	}
+}
+
+func TestDisplaySessions_NoColor(t *testing.T) {
+	sessions := []Session{
+		{
+			Process:   Process{PID: 100, Cwd: "/tmp"},
+			State:     Working,
+			CwdPath:   "/tmp",
+			GitBranch: "main",
+		},
+	}
+
+	var buf bytes.Buffer
+	DisplaySessions(&buf, sessions, true)
+	output := buf.String()
+
+	if strings.Contains(output, "\033") {
+		t.Errorf("noColor=true but output contains ANSI escape: %q", output)
+	}
+	if !strings.Contains(output, "Working") {
+		t.Error("output missing state label")
+	}
+}
+
+func TestDisplaySessions_Empty(t *testing.T) {
+	var buf bytes.Buffer
+	DisplaySessions(&buf, nil, false)
+	output := buf.String()
+
+	want := "No active Claude Code sessions found.\n"
+	if output != want {
+		t.Errorf("output = %q, want %q", output, want)
+	}
+}
+
+func TestDisplaySessions_WorktreeDiffers(t *testing.T) {
+	sessions := []Session{
+		{
+			Process:  Process{PID: 100, Cwd: "/home/user/repo/src"},
+			State:    Working,
+			CwdPath:  "/home/user/repo/src",
+			Worktree: "/home/user/repo",
+		},
+	}
+
+	var buf bytes.Buffer
+	DisplaySessions(&buf, sessions, true)
+	output := buf.String()
+
+	if !strings.Contains(output, "[worktree: /home/user/repo]") {
+		t.Errorf("output should show worktree when different from cwd: %q", output)
+	}
+}
+
+func TestDisplaySessions_NoBranch(t *testing.T) {
+	sessions := []Session{
+		{
+			Process: Process{PID: 100, Cwd: "/tmp"},
+			State:   Unknown,
+			CwdPath: "/tmp",
+		},
+	}
+
+	var buf bytes.Buffer
+	DisplaySessions(&buf, sessions, true)
+	output := buf.String()
+
+	if strings.Contains(output, "(") {
+		t.Errorf("no branch should mean no parentheses: %q", output)
+	}
+}

main.go

@@ -1,5 +1,98 @@
 package main
 
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
 func main() {
-	// Placeholder - will be implemented in Task 2
+	noColor := flag.Bool("no-color", false, "Disable colored output")
+	flag.Parse()
+
+	if os.Getenv("NO_COLOR") != "" {
+		*noColor = true
+	}
+
+	args := flag.Args()
+	// Also check for --no-color after subcommand (flag stops at first non-flag)
+	var filteredArgs []string
+	for _, arg := range args {
+		if arg == "--no-color" {
+			*noColor = true
+		} else {
+			filteredArgs = append(filteredArgs, arg)
+		}
+	}
+
+	if len(filteredArgs) == 0 || filteredArgs[0] != "list" {
+		fmt.Fprintf(os.Stderr, "Usage: vmux list [--no-color]\n")
+		os.Exit(1)
+	}
+
+	processes, err := FindClaudeProcesses("/proc")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error scanning processes: %v\n", err)
+		os.Exit(1)
+	}
+
+	claudeDir := filepath.Join(os.Getenv("HOME"), ".claude", "projects")
+	now := time.Now()
+	var sessions []Session
+
+	for _, proc := range processes {
+		jsonlPath, messages, err := FindSessionForProcess(claudeDir, proc)
+		if err != nil {
+			sessions = append(sessions, Session{
+				Process: proc,
+				State:   Unknown,
+				CwdPath: proc.Cwd,
+			})
+			continue
+		}
+
+		state := DetectState(messages, now)
+		preview := ExtractPreview(messages)
+
+		var sessionID, gitBranch string
+		for _, msg := range messages {
+			if msg.SessionID != "" {
+				sessionID = msg.SessionID
+			}
+			if msg.GitBranch != "" {
+				gitBranch = msg.GitBranch
+			}
+		}
+
+		worktree := resolveWorktree(proc.Cwd)
+
+		_ = jsonlPath
+
+		sessions = append(sessions, Session{
+			Process:   proc,
+			SessionID: sessionID,
+			GitBranch: gitBranch,
+			State:     state,
+			Preview:   preview,
+			CwdPath:   proc.Cwd,
+			Worktree:  worktree,
+		})
+	}
+
+	DisplaySessions(os.Stdout, sessions, *noColor)
+}
+
+// resolveWorktree uses git to find the worktree root.
+// Falls back to cwd if git fails (not a git repo).
+func resolveWorktree(cwd string) string {
+	cmd := exec.Command("git", "-C", cwd, "rev-parse", "--show-toplevel")
+	out, err := cmd.Output()
+	if err != nil {
+		return cwd
+	}
+	return strings.TrimSpace(string(out))
 }