Cache file causes crashes when adding rulesets

[kapsh]

Describe the bug
Enabled cache file causes crashes when trying to add rulesets.

To Reproduce
Steps to reproduce the behavior:

1. On Rules tab add some ruleset and save.
   I used remote https://raw.githubusercontent.com/runetfreedom/russia-v2ray-rules-dat/release/sing-box/rule-set-geosite/geosite-category-ads-all.srs
2. On Experimental tab enable cache file and save.
   Alternatively, enable cache and start adding rulesets, backtrace is similar.
3. See error

./s-ui/sui
2026/02/24 18:17:39 s-ui 1.3.10
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x128 pc=0xdd212e]

goroutine 42 [running]:
internal/sync.(*Mutex).Lock(...)
        /opt/hostedtoolcache/go/1.25.7/x64/src/internal/sync/mutex.go:63
sync.(*Mutex).Lock(...)
        /opt/hostedtoolcache/go/1.25.7/x64/src/sync/mutex.go:46
github.com/sagernet/bbolt.(*DB).beginTx(0x0)
        /home/runner/go/pkg/mod/github.com/sagernet/bbolt@v0.0.0-20231014093535-ea5cb2fe9f0a/db.go:707 +0x2e
github.com/sagernet/bbolt.(*DB).Begin(0xc000451520?, 0x5?)
        /home/runner/go/pkg/mod/github.com/sagernet/bbolt@v0.0.0-20231014093535-ea5cb2fe9f0a/db.go:700 +0x25
github.com/sagernet/bbolt.(*DB).View(0xc000451598?, 0xc0000b9d68)
        /home/runner/go/pkg/mod/github.com/sagernet/bbolt@v0.0.0-20231014093535-ea5cb2fe9f0a/db.go:864 +0x30
github.com/sagernet/sing-box/experimental/cachefile.(*CacheFile).LoadRuleSet(0xc0005e8630, {0xc00061b5d0, 0x6})
        /home/runner/go/pkg/mod/github.com/sagernet/sing-box@v1.12.21/experimental/cachefile/cache.go:289 +0x85
github.com/sagernet/sing-box/route/rule.(*RemoteRuleSet).StartContext(0xc0001796c0, {0x30b3a20, 0xc0005d6b90}, 0xc0002255e0)
        /home/runner/go/pkg/mod/github.com/sagernet/sing-box@v1.12.21/route/rule/rule_set_remote.go:98 +0x21e
github.com/sagernet/sing-box/route.(*Router).Start.func1({0x30b3a20?, 0xc0005d6b90?})
        /home/runner/go/pkg/mod/github.com/sagernet/sing-box@v1.12.21/route/router.go:98 +0x49
github.com/sagernet/sing/common/task.(*Group).Run.func1()
        /home/runner/go/pkg/mod/github.com/sagernet/sing@v0.7.18/common/task/task.go:83 +0x107
created by github.com/sagernet/sing/common/task.(*Group).Run in goroutine 69
        /home/runner/go/pkg/mod/github.com/sagernet/sing@v0.7.18/common/task/task.go:67 +0x125

Expected behavior
Expected that cache file works: plain sing-box (same version as bundled 1.12.21) supports rulesets and cache at the same time (though only after restart).

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS] Linux amd64
• Browser [e.g. chrome, safari]
• Version [e.g. 22] 1.3.10

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[alireza0]

Thank you for your report.
It was one of several problems happened due to a bug in save basic configurations.
All fixed.