test(scheduler): capture logs in a lock-guarded buffer (fixes the data race failing main)

internal/scheduler/recommendation_completeness_integration_test.go

@@ -26,6 +26,27 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// lockedBuffer is a bytes.Buffer safe for concurrent use. The test captures
+// the process-wide logger, and connection pools from other subtests on the
+// shared Postgres server (#1400) can still log from background goroutines
+// (pgxpool's idle-connection creation) while the test reads the capture.
+type lockedBuffer struct {
+	mu  sync.Mutex
+	buf bytes.Buffer
+}
+
+func (b *lockedBuffer) Write(p []byte) (int, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.buf.Write(p)
+}
+
+func (b *lockedBuffer) String() string {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.buf.String()
+}
+
 type completenessHTTP struct {
 	resourceType string
 	accounts     []any
@@ -205,7 +226,7 @@ func TestAWSRecommendationCompletenessPersistence(t *testing.T) {
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			ctx := context.Background()
-			var diagnostics bytes.Buffer
+			var diagnostics lockedBuffer
 			previous := logging.SetOutput(&diagnostics)
 			t.Cleanup(func() { logging.SetOutput(previous) })
 			container := testhelpers.RequireMigratedDatabase(ctx, t, "../database/postgres/migrations")