feat(go): step 2 — per-phase request breakdown via httptrace

Instruments HTTP requests with net/http/httptrace.ClientTrace to capture
timestamps for DNS, TCP connect, TLS handshake, TTFB, and body transfer.
TLS row is omitted automatically for plain http:// URLs. Output is an
aligned text table with a separator before the Total row.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go/main.go

@@ -4,7 +4,7 @@ import (
 	"flag"
 	"fmt"
 	"os"
-	"time"
+	"strings"
 
 	"latprobe/internal/probe"
 )
@@ -44,17 +44,48 @@ func main() {
 	_ = count
 
 	failed := false
-	for _, url := range urls {
+	for i, url := range urls {
+		if i > 0 {
+			fmt.Println()
+		}
 		r := probe.Measure(url)
 		if r.Err != nil {
-			fmt.Fprintf(os.Stderr, "error %s: %v\n", url, r.Err)
+			fmt.Fprintf(os.Stderr, "error %s: %v\n", r.URL, r.Err)
 			failed = true
 			continue
 		}
-		fmt.Printf("%-45s  %d  %v\n", r.URL, r.StatusCode, r.Total.Duration.Round(time.Millisecond))
+		printResult(r)
 	}
 
 	if failed {
 		os.Exit(1)
 	}
 }
+
+func printResult(r probe.Result) {
+	fmt.Printf("%s  (%d)\n", r.URL, r.StatusCode)
+
+	phases := []struct {
+		label string
+		p     probe.Phase
+	}{
+		{"DNS lookup    ", r.DNS},
+		{"TCP connect   ", r.Connect},
+		{"TLS handshake ", r.TLS},
+		{"Server (TTFB) ", r.TTFB},
+		{"Transfer      ", r.Transfer},
+	}
+
+	for _, ph := range phases {
+		if ph.p.Present {
+			fmt.Printf("  %s :  %8.2f ms\n", ph.label, msec(ph.p))
+		}
+	}
+
+	fmt.Println("  " + strings.Repeat("─", 29))
+	fmt.Printf("  %s :  %8.2f ms\n", "Total         ", msec(r.Total))
+}
+
+func msec(p probe.Phase) float64 {
+	return float64(p.Duration.Microseconds()) / 1000
+}