when hy2 realm network is unstable, crash on no STUN responses received.

### Operating system Linux ### System version Ubuntu 24.04 ### Installation type Original sing-box Command Line ### If you are using a graphical client, please provide the version of the client. _No response_ ### Version ```shell 1.14.0-alpha.22 ``` ### Description when network is unstable,hy2 realm should retry with a set interval instead of crash on no STUN responses received. ### Reproduction 1. configure hy2 with realm 2. unplug network cable 3. start sing-box 4. connect to network 5. sing-box crash ### Logs ```shell +0000 2026-05-12 04:29:11 WARN inbound: close inbound/hysteria2[hysteria2] take too much time to finish! ERROR[0024] sing-box did not closed properly: file already closed start inbound/hysteria2[hysteria2]: start realm server: initial STUN discovery: no STUN responses received goroutine 1 [running]: runtime/debug.Stack() runtime/debug/stack.go:26 +0x5e runtime/debug.PrintStack() runtime/debug/stack.go:18 +0x13 github.com/sagernet/sing-box.(*Box).Start.func1() github.com/sagernet/sing-box/box.go:479 +0x96 panic({0x49bdc0?, 0x475a670?}) runtime/panic.go:783 +0x132 internal/sync.(*Mutex).Lock(...) internal/sync/mutex.go:63 sync.(*Mutex).Lock(...) sync/mutex.go:46 github.com/sagernet/fswatch.(*Watcher).Close(0x0) github.com/sagernet/fswatch@v0.1.2/watcher.go:107 +0x3c github.com/sagernet/sing/common.Close({0xc000ac71a8?, 0x1?, 0x0?}) github.com/sagernet/sing@v0.8.10-0.20260428084616-2bc976d03e39/common/cond.go:361 +0x15b github.com/sagernet/sing-box/common/tls.(*STDServerConfig).Close(0x2414be5?) github.com/sagernet/sing-box/common/tls/std_server.go:323 +0x85 github.com/sagernet/sing/common.Close({0xc000ac7268?, 0xc000ac7298?, 0x24a8f95?}) github.com/sagernet/sing@v0.8.10-0.20260428084616-2bc976d03e39/common/cond.go:361 +0x15b github.com/sagernet/sing-box/protocol/hysteria2.(*Inbound).Close(0xc0003f23e0?) github.com/sagernet/sing-box/protocol/hysteria2/inbound.go:257 +0x86 github.com/sagernet/sing-box/adapter/inbound.(*Manager).Close(0xc000198d20) github.com/sagernet/sing-box/adapter/inbound/manager.go:74 +0x45b github.com/sagernet/sing-box.(*Box).Close(0xc0006e5d40) github.com/sagernet/sing-box/box.go:585 +0x282 github.com/sagernet/sing-box.(*Box).Start(0xc0006e5d40) github.com/sagernet/sing-box/box.go:483 +0x194 main.create() github.com/sagernet/sing-box/cmd/sing-box/cmd_run.go:160 +0x456 main.run() github.com/sagernet/sing-box/cmd/sing-box/cmd_run.go:174 +0x105 main.init.func26(0xc000326b00?, {0x937de3?, 0x4?, 0x937de7?}) github.com/sagernet/sing-box/cmd/sing-box/cmd_run.go:30 +0x17 github.com/spf13/cobra.(*Command).execute(0x478f940, {0xc0002bd6a0, 0x2, 0x2}) github.com/spf13/cobra@v1.10.2/command.go:1019 +0xae7 github.com/spf13/cobra.(*Command).ExecuteC(0x478a8c0) github.com/spf13/cobra@v1.10.2/command.go:1148 +0x465 github.com/spf13/cobra.(*Command).Execute(...) github.com/spf13/cobra@v1.10.2/command.go:1071 main.main() github.com/sagernet/sing-box/cmd/sing-box/main.go:8 +0x1e panic on early start: runtime error: invalid memory address or nil pointer dereference ``` ### Supporter - [ ] I am a [sponsor](https://github.com/sponsors/nekohasekai/) ### Integrity requirements - [x] I confirm that I have read the documentation, understand the meaning of all the configuration items I wrote, and did not pile up seemingly useful options or default values. - [x] I confirm that I have provided the server and client configuration files and process that can be reproduced locally, instead of a complicated client configuration file that has been stripped of sensitive data. - [x] I confirm that I have provided the simplest configuration that can be used to reproduce the error I reported, instead of depending on remote servers, TUN, graphical interface clients, or other closed-source software. - [x] I confirm that I have provided the complete configuration files and logs, rather than just providing parts I think are useful out of confidence in my own intelligence.