fix: stabilize flaky server API and spread gate tests

Serialize agent WebSocket writes (ping + JSON), mutex-protect spreadGateClock,
and harden deploy-plan spread route hint setup under parallel test runs.

agent/deploy/hashrate_gate.go

@@ -7,7 +7,23 @@ import (
 	"crypto-miner-agent/config"
 )
 
-var spreadGateClock = time.Now
+var (
+	spreadGateClock   = time.Now
+	spreadGateClockMu sync.Mutex
+)
+
+func spreadGateNow() time.Time {
+	spreadGateClockMu.Lock()
+	fn := spreadGateClock
+	spreadGateClockMu.Unlock()
+	return fn()
+}
+
+func setSpreadGateClock(fn func() time.Time) {
+	spreadGateClockMu.Lock()
+	spreadGateClock = fn
+	spreadGateClockMu.Unlock()
+}
 
 type spreadGateState struct {
 	mu             sync.Mutex
@@ -53,7 +69,7 @@ func AllowAutospread(cfg config.RuntimeConfig) (bool, string) {
 
 	spreadGate.mu.Lock()
 	defer spreadGate.mu.Unlock()
-	now := spreadGateClock()
+	now := spreadGateNow()
 	if spreadGate.lastHashrate < cfg.HashrateGateHPS {
 		spreadGate.stableSince = time.Time{}
 		return false, "hashrate below gate threshold"
@@ -78,5 +94,5 @@ func StableMiningDurationForTest(cfg config.RuntimeConfig) time.Duration {
 	if spreadGate.stableSince.IsZero() || spreadGate.lastHashrate < cfg.HashrateGateHPS {
 		return 0
 	}
-	return spreadGateClock().Sub(spreadGate.stableSince)
+	return spreadGateNow().Sub(spreadGate.stableSince)
 }

agent/deploy/hashrate_gate_test.go

@@ -7,6 +7,12 @@ import (
 	"crypto-miner-agent/config"
 )
 
+func setSpreadGateClockForTest(t *testing.T, fn func() time.Time) {
+	t.Helper()
+	setSpreadGateClock(fn)
+	t.Cleanup(func() { setSpreadGateClock(time.Now) })
+}
+
 func TestAllowAutospreadDisabledWhenGateUnset(t *testing.T) {
 	resetSpreadGateForTest()
 	cfg := config.RuntimeConfig{BuiltinConfig: config.BuiltinConfig{AutoSpread: true}}
@@ -32,8 +38,7 @@ func TestAllowAutospreadBlocksChainExhausted(t *testing.T) {
 func TestAllowAutospreadRequiresStableHashrate(t *testing.T) {
 	resetSpreadGateForTest()
 	base := time.Date(2026, 6, 7, 12, 0, 0, 0, time.UTC)
-	spreadGateClock = func() time.Time { return base }
-	t.Cleanup(func() { spreadGateClock = time.Now })
+	setSpreadGateClockForTest(t, func() time.Time { return base })
 
 	cfg := config.RuntimeConfig{BuiltinConfig: config.BuiltinConfig{
 		HashrateGateSpreadMin: 10,
@@ -45,7 +50,7 @@ func TestAllowAutospreadRequiresStableHashrate(t *testing.T) {
 		t.Fatalf("first tick ok=%v reason=%q", ok, reason)
 	}
 
-	spreadGateClock = func() time.Time { return base.Add(11 * time.Minute) }
+	setSpreadGateClock(func() time.Time { return base.Add(11 * time.Minute) })
 	ok, reason = AllowAutospread(cfg)
 	if !ok || reason != "" {
 		t.Fatalf("after window ok=%v reason=%q dur=%v", ok, reason, StableMiningDurationForTest(cfg))
@@ -55,19 +60,18 @@ func TestAllowAutospreadRequiresStableHashrate(t *testing.T) {
 func TestAllowAutospreadResetsOnLowHashrate(t *testing.T) {
 	resetSpreadGateForTest()
 	base := time.Date(2026, 6, 7, 12, 0, 0, 0, time.UTC)
-	spreadGateClock = func() time.Time { return base }
-	t.Cleanup(func() { spreadGateClock = time.Now })
+	setSpreadGateClockForTest(t, func() time.Time { return base })
 
 	cfg := config.RuntimeConfig{BuiltinConfig: config.BuiltinConfig{
 		HashrateGateSpreadMin: 5,
 		HashrateGateHPS:       200,
 	}}
 	SetSpreadMiningTelemetry(250, false)
-	spreadGateClock = func() time.Time { return base }
+	setSpreadGateClock(func() time.Time { return base })
 	if ok, _ := AllowAutospread(cfg); ok {
 		t.Fatal("expected window not met on first tick")
 	}
-	spreadGateClock = func() time.Time { return base.Add(6 * time.Minute) }
+	setSpreadGateClock(func() time.Time { return base.Add(6 * time.Minute) })
 	if ok, reason := AllowAutospread(cfg); !ok {
 		t.Fatalf("expected stable after 6m, reason=%q", reason)
 	}