test(server): synchronize startup watchdog log capture

TestStartupWatchdogLogsPhaseAndStack polls a bytes.Buffer while the watchdog goroutine writes the same buffer through zerolog, so 'go test -race' reports a read/write data race at service_health_test.go:134 and fails the rest-0 backend shard. Capture the log through a mutex-guarded buffer so the poll and the watchdog write are serialized.

Change-source: pulse-maintainer

pkg/server/service_health_test.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/http"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -118,12 +119,31 @@ func TestFrontendAssetPathsStayLocalAndBounded(t *testing.T) {
 	}
 }
 
+// syncBuffer is a goroutine-safe bytes.Buffer for capturing watchdog log output
+// written from another goroutine while the test polls it.
+type syncBuffer struct {
+	mu  sync.Mutex
+	buf bytes.Buffer
+}
+
+func (b *syncBuffer) Write(p []byte) (int, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.buf.Write(p)
+}
+
+func (b *syncBuffer) String() string {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.buf.String()
+}
+
 // A bound-but-not-serving listener is otherwise undiagnosable: nothing accepts
 // connections and no startup log line is emitted while a synchronous step
 // stalls. The watchdog must name the last completed phase and dump the local
 // goroutine stacks so a recurrence can be read from the field log.
 func TestStartupWatchdogLogsPhaseAndStack(t *testing.T) {
-	var buf bytes.Buffer
+	var buf syncBuffer
 	phase := &startupPhase{}
 	phase.mark("config watcher started")