feat(go): add load simulator hold mode

docs/ops/100k-capacity-baseline.md

@@ -84,7 +84,8 @@ go run ./cmd/load-sim \
   -connect-rate 100 \
   -send-interval 10s \
   -duration 2m \
-  -template 0200
+  -template 0200 \
+  -send=false
 ```
 
 1. 100 连接 smoke test。

docs/ops/vehicle-ingest-runbook.md

@@ -104,7 +104,8 @@ go run ./cmd/load-sim \
   -connect-rate 100 \
   -send-interval 10s \
   -duration 2m \
-  -template 0200
+  -template 0200 \
+  -send=false
 ```
 
 ## 告警阈值建议

docs/superpowers/plans/2026-07-03-100k-vehicle-ingest-hardening.md

@@ -488,7 +488,7 @@ Extend load-sim to open N TCP connections and keep them open for `duration`, wit
 Expected CLI:
 
 ```bash
-go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 10000 -send-interval 30s -duration 5m
+go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 10000 -send-interval 30s -duration 5m -send=false
 ```
 
 - [ ] **Step 2: Run from non-production client**
@@ -496,7 +496,7 @@ go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 1000
 Run a small smoke first:
 
 ```bash
-go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 100 -duration 30s
+go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 100 -duration 30s -send=false
 ```
 
 Then run 10K only after smoke succeeds.

go/vehicle-gateway/internal/loadsim/config.go

@@ -24,6 +24,7 @@ type Config struct {
 	SendInterval         time.Duration
 	Duration             time.Duration
 	Template             string
+	SendFrames           bool
 }
 
 type FlagConfig struct {
@@ -34,6 +35,7 @@ type FlagConfig struct {
 	sendInterval time.Duration
 	duration     time.Duration
 	template     string
+	sendFrames   bool
 }
 
 func RegisterFlags(fs *flag.FlagSet) *FlagConfig {
@@ -45,6 +47,7 @@ func RegisterFlags(fs *flag.FlagSet) *FlagConfig {
 	fs.DurationVar(&cfg.sendInterval, "send-interval", 10*time.Second, "frame send interval per connection")
 	fs.DurationVar(&cfg.duration, "duration", 10*time.Minute, "load test duration")
 	fs.StringVar(&cfg.template, "template", "", "frame template name")
+	fs.BoolVar(&cfg.sendFrames, "send", true, "send protocol frames while connections are open")
 	return cfg
 }
 
@@ -78,5 +81,6 @@ func (c *FlagConfig) Build() (Config, error) {
 		SendInterval:         c.sendInterval,
 		Duration:             c.duration,
 		Template:             strings.TrimSpace(c.template),
+		SendFrames:           c.sendFrames,
 	}, nil
 }

go/vehicle-gateway/internal/loadsim/config_test.go

@@ -18,6 +18,7 @@ func TestConfigFromFlagsParsesCapacityKnobs(t *testing.T) {
 		"-send-interval", "5s",
 		"-duration", "30m",
 		"-template", "0200",
+		"-send=false",
 	})
 	if err != nil {
 		t.Fatalf("parse flags: %v", err)
@@ -49,6 +50,9 @@ func TestConfigFromFlagsParsesCapacityKnobs(t *testing.T) {
 	if got.Template != "0200" {
 		t.Fatalf("Template = %q", got.Template)
 	}
+	if got.SendFrames {
+		t.Fatal("SendFrames = true, want false")
+	}
 }
 
 func TestConfigFromFlagsRejectsUnsafeValues(t *testing.T) {

go/vehicle-gateway/internal/loadsim/runner.go

@@ -37,6 +37,9 @@ func (r Runner) Run(ctx context.Context, cfg Config) (Stats, error) {
 	if err != nil {
 		return Stats{}, err
 	}
+	if !cfg.SendFrames {
+		payload = nil
+	}
 	dial := r.Dial
 	if dial == nil {
 		dialer := &net.Dialer{Timeout: 5 * time.Second, KeepAlive: 30 * time.Second}
@@ -68,7 +71,11 @@ func (r Runner) Run(ctx context.Context, cfg Config) (Stats, error) {
 			go func() {
 				defer wg.Done()
 				defer conn.Close()
-				writeLoop(runCtx, conn, payload, cfg.SendInterval, &stats)
+				if cfg.SendFrames {
+					writeLoop(runCtx, conn, payload, cfg.SendInterval, &stats)
+					return
+				}
+				<-runCtx.Done()
 			}()
 		}
 	}

go/vehicle-gateway/internal/loadsim/runner_test.go

@@ -34,6 +34,7 @@ func TestRunnerDialsTargetConnectionsAndWritesFrames(t *testing.T) {
 		SendInterval:         time.Millisecond,
 		Duration:             5 * time.Millisecond,
 		Template:             "0200",
+		SendFrames:           true,
 	})
 	if err != nil {
 		t.Fatalf("Run() error = %v", err)
@@ -53,6 +54,41 @@ func TestRunnerDialsTargetConnectionsAndWritesFrames(t *testing.T) {
 	}
 }
 
+func TestRunnerCanHoldConnectionsWithoutWritingFrames(t *testing.T) {
+	var writes atomic.Int64
+	runner := Runner{
+		Dial: func(ctx context.Context, network, addr string) (net.Conn, error) {
+			return &recordingConn{
+				write: func(p []byte) (int, error) {
+					writes.Add(1)
+					return len(p), nil
+				},
+				close: func() error { return nil },
+			}, nil
+		},
+	}
+
+	stats, err := runner.Run(context.Background(), Config{
+		Protocol:             ProtocolJT808,
+		Addr:                 "127.0.0.1:808",
+		Connections:          2,
+		ConnectRatePerSecond: 1000,
+		SendInterval:         time.Millisecond,
+		Duration:             5 * time.Millisecond,
+		Template:             "0200",
+		SendFrames:           false,
+	})
+	if err != nil {
+		t.Fatalf("Run() error = %v", err)
+	}
+	if stats.ConnectionsOpened != 2 {
+		t.Fatalf("ConnectionsOpened = %d, want 2", stats.ConnectionsOpened)
+	}
+	if stats.FramesWritten != 0 || writes.Load() != 0 {
+		t.Fatalf("frames written stats=%d writes=%d, want 0", stats.FramesWritten, writes.Load())
+	}
+}
+
 type recordingConn struct {
 	write func([]byte) (int, error)
 	close func() error