fix: data races in NBD path_direct and PostProcessor test on ARM64

- path_direct.go: capture deviceIndex before goroutine closure. The
  outer for-loop is not a range loop, so Go 1.22+ loop variable fix
  doesn't apply — deviceIndex is reassigned on each retry iteration.
- postprocessor_test.go: use sync.Mutex-wrapped buffer instead of bare
  bytes.Buffer. The PostProcessor goroutine and test goroutine write
  to the buffer concurrently.

Both races were exposed by running tests with -race on ARM64 (weaker
memory model makes races more likely to manifest).

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

Author: 2 people

packages/orchestrator/pkg/sandbox/nbd/path_direct.go

@@ -78,7 +78,7 @@ func (d *DirectPathMount) Open(ctx context.Context) (retDeviceIndex uint32, err
 
 	telemetry.ReportEvent(ctx, "got backend size")
 
-	deviceIndex := uint32(math.MaxUint32)
+	var deviceIndex uint32
 
 	for {
 		deviceIndex, err = d.devicePool.GetDevice(ctx)
@@ -119,13 +119,17 @@ func (d *DirectPathMount) Open(ctx context.Context) (retDeviceIndex uint32, err
 			server.Close()
 
 			dispatch := NewDispatch(serverc, d.Backend)
+			// Capture deviceIndex for the goroutine closure — it's reassigned on
+			// each retry iteration of the outer for-loop (not a range loop, so
+			// Go 1.22+ loop variable fix doesn't apply).
+			devIdx := deviceIndex
 			// Start reading commands on the socket and dispatching them to our provider
 			d.handlersWg.Go(func() {
 				handleErr := dispatch.Handle(ctx)
 				// The error is expected to happen if the nbd (socket connection) is closed
 				logger.L().Info(ctx, "closing handler for NBD commands",
 					zap.Error(handleErr),
-					zap.Uint32("device_index", deviceIndex),
+					zap.Uint32("device_index", devIdx),
 					zap.Int("socket_index", i),
 				)
 			})

packages/orchestrator/pkg/template/build/writer/postprocessor_test.go

@@ -2,6 +2,7 @@ package writer
 
 import (
 	"bytes"
+	"sync"
 	"testing"
 	"time"
 
@@ -12,14 +13,37 @@ import (
 	"github.com/e2b-dev/infra/packages/shared/pkg/logger"
 )
 
-func newTestCore(buf *bytes.Buffer) zapcore.Core {
+// syncBuffer wraps bytes.Buffer with a mutex for concurrent writes from
+// the PostProcessor goroutine and the test goroutine.
+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) Sync() error { return nil }
+
+func (b *syncBuffer) String() string {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	return b.buf.String()
+}
+
+func newTestCore(buf *syncBuffer) zapcore.Core {
 	encoderCfg := zap.NewDevelopmentEncoderConfig()
 	encoderCfg.TimeKey = ""
 	encoder := zapcore.NewConsoleEncoder(encoderCfg)
 
 	core := zapcore.NewCore(
 		encoder,
-		zapcore.AddSync(buf),
+		buf,
 		zapcore.DebugLevel,
 	)
 
@@ -29,7 +53,7 @@ func newTestCore(buf *bytes.Buffer) zapcore.Core {
 func TestPostProcessor_Start(t *testing.T) {
 	t.Parallel()
 	ctx := t.Context()
-	var buf bytes.Buffer
+	var buf syncBuffer
 	core := newTestCore(&buf)
 
 	interval := time.Millisecond * 100