test(04-02): add i3bar formatting with TDD

- I3BarBlock struct for i3bar protocol JSON
- formatI3BarBlocks: compact format D-06/D-07/D-08
- 10 tests covering mixed states, colors, labels, markers

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

i3bar_test.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestFormatI3BarBlocks_MixedStates(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/home/pierre/Code/auth", State: "Needs Input"},
+		{Cwd: "/home/pierre/Code/portal", State: "Working"},
+		{Cwd: "/home/pierre/Code/neia", State: "Idle"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	if len(blocks) != 1 {
+		t.Fatalf("expected 1 block, got %d", len(blocks))
+	}
+	want := "vmux: auth[!] portal[W] neia[I]"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+	if blocks[0].Color != "#ff0000" {
+		t.Errorf("color = %q, want #ff0000", blocks[0].Color)
+	}
+}
+
+func TestFormatI3BarBlocks_AllWorking(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/a/b/one", State: "Working"},
+		{Cwd: "/a/b/two", State: "Working"},
+		{Cwd: "/a/b/three", State: "Working"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: all working (3)"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+	if blocks[0].Color != "#00ff00" {
+		t.Errorf("color = %q, want #00ff00", blocks[0].Color)
+	}
+}
+
+func TestFormatI3BarBlocks_NoSessions(t *testing.T) {
+	blocks := formatI3BarBlocks(nil)
+	want := "vmux: no sessions"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+	if blocks[0].Color != "#00ff00" {
+		t.Errorf("color = %q, want #00ff00", blocks[0].Color)
+	}
+}
+
+func TestFormatI3BarBlocks_ColorRed(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/a/b/x", State: "Working"},
+		{Cwd: "/a/b/y", State: "Needs Input"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	if blocks[0].Color != "#ff0000" {
+		t.Errorf("color = %q, want #ff0000", blocks[0].Color)
+	}
+}
+
+func TestFormatI3BarBlocks_ColorGreen(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/a/b/x", State: "Working"},
+		{Cwd: "/a/b/y", State: "Idle"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	if blocks[0].Color != "#00ff00" {
+		t.Errorf("color = %q, want #00ff00", blocks[0].Color)
+	}
+}
+
+func TestFormatI3BarBlocks_UsesLabel(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/home/pierre/Code/auth-service", Label: "auth", State: "Working"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: all working (1)"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+}
+
+func TestFormatI3BarBlocks_UsesLabelInMixed(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/home/pierre/Code/auth-service", Label: "auth", State: "Needs Input"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: auth[!]"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+}
+
+func TestFormatI3BarBlocks_UsesCwdBase(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/home/pierre/Code/vibe/vmux", State: "Needs Input"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: vmux[!]"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+}
+
+func TestFormatI3BarBlocks_NeedsInputMarker(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/a/proj", State: "Needs Input"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: proj[!]"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+}
+
+func TestFormatI3BarBlocks_IdleMarker(t *testing.T) {
+	sessions := []SessionInfo{
+		{Cwd: "/a/proj", State: "Idle"},
+		{Cwd: "/a/other", State: "Needs Input"},
+	}
+	blocks := formatI3BarBlocks(sessions)
+	want := "vmux: proj[I] other[!]"
+	if blocks[0].FullText != want {
+		t.Errorf("full_text = %q, want %q", blocks[0].FullText, want)
+	}
+}