Write config.json after a hot apply (#6686)

* Write config.json after a hot apply

tryHotApply only updated the in-memory snapshot, so bin/config.json stayed
stale until the next cold start and the Telegram/Discord config backups
uploaded old rules. Persist the new config once the API calls succeed; a
write failure is logged and does not restart the running core.

* Test that a hot apply refreshes config.json

internal/web/service/xray.go

@@ -1454,6 +1454,7 @@ func (s *XrayService) tryHotApply(process *xray.Process, newCfg *xray.Config) bo
 	}
 	if diff.Empty() {
 		process.SetConfig(newCfg)
+		persistHotConfig(process)
 		return true
 	}
 	// The core's RemoveUser drops the credential only, so a disabled or deleted
@@ -1522,9 +1523,18 @@ func (s *XrayService) tryHotApply(process *xray.Process, newCfg *xray.Config) bo
 	}
 
 	process.SetConfig(newCfg)
+	persistHotConfig(process)
 	return true
 }
 
+// persistHotConfig refreshes config.json after a hot apply; a write failure is
+// logged only, since the running core already has the change.
+func persistHotConfig(process *xray.Process) {
+	if err := process.PersistConfig(); err != nil {
+		logger.Warning("hot apply: failed to update config.json:", err)
+	}
+}
+
 // addUserReconciling adds a user, and on an email conflict (the user was
 // already applied through the runtime API) replaces the existing user instead.
 func addUserReconciling(api *xray.XrayAPI, u xray.UserOp) error {

internal/web/service/xray_hot_apply_persist_test.go

@@ -0,0 +1,25 @@
+package service
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/util/json_util"
+	"github.com/mhsanaei/3x-ui/v3/internal/xray"
+)
+
+// The empty-diff branch of tryHotApply makes no gRPC call, so it can prove the
+// hot-apply path refreshes config.json without a running core.
+func TestTryHotApplyWritesConfigFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	routing := json_util.RawMessage(`{"rules":[]}`)
+	process := xray.NewTestProcess(&xray.Config{RouterConfig: routing}, path)
+
+	if !(&XrayService{}).tryHotApply(process, &xray.Config{RouterConfig: routing}) {
+		t.Fatal("tryHotApply = false, want true for an unchanged config")
+	}
+	if data, err := os.ReadFile(path); err != nil || len(data) == 0 {
+		t.Fatalf("config.json not written after hot apply (err %v)", err)
+	}
+}