fix(dns): preserve 127.0.0.42 during restart and add local DNS cache support

- decouple restart() from stop_impl() in lifecycle.uc to avoid premature dnsmasq_restore
- keep dhcp.@dnsmasq[0].server locked to 127.0.0.42 throughout service restarts
- add atomic restart_service hooks in init.d/tachyon and initd.uc
- fix dns_turbo_cache path resolution to promote default cache to /etc/sing-box/cache.db
- add Local DNS Cache support in dnsmasq (dns_local_cache, dns_cache_size)
- add comprehensive behavioral regression test tests/service_restart_lifecycle.sh

luci-app-tachyon/htdocs/luci-static/resources/view/tachyon/settings.js

@@ -1853,6 +1853,30 @@ function createSettingsContent(section, capabilities) {
   o.default = "0";
   o.rmempty = false;
 
+  o = section.taboption(
+    "dns",
+    form.Flag,
+    "dns_local_cache",
+    _("Local DNS Cache"),
+    _(
+      "Enables high-capacity local DNS caching in dnsmasq to accelerate DNS queries and absorb transient latency during service restarts.",
+    ),
+  );
+  o.default = "0";
+  o.rmempty = false;
+
+  o = section.taboption(
+    "dns",
+    form.Value,
+    "dns_cache_size",
+    _("DNS Cache Size"),
+    _("Number of cached DNS domain entries in dnsmasq (default: 10000)."),
+  );
+  o.depends("dns_local_cache", "1");
+  o.default = "10000";
+  o.datatype = "uinteger";
+  o.rmempty = true;
+
   // ─── DNS Strategy ────────────────────────────────────────────────────────
 
   o = section.taboption(

luci-app-tachyon/po/ru/tachyon.po

@@ -7,8 +7,8 @@ msgid ""
 msgstr ""
 "Project-Id-Version: TACHYON\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2026-09-17 08:13+0300\n"
-"PO-Revision-Date: 2026-09-17 08:13+0300\n"
+"POT-Creation-Date: 2026-09-17 08:45+0300\n"
+"PO-Revision-Date: 2026-09-17 08:45+0300\n"
 "Last-Translator: Dushnilin\n"
 "Language-Team: none\n"
 "Language: ru\n"
@@ -1439,6 +1439,9 @@ msgstr "Автоподбор и бенчмарк DNS"
 msgid "DNS Blocking"
 msgstr "Блокировка DNS"
 
+msgid "DNS Cache Size"
+msgstr ""
+
 msgid "DNS Check Interval"
 msgstr "Интервал проверки DNS"
 
@@ -1793,6 +1796,9 @@ msgstr "Включено"
 msgid "Enabled (always prioritize)"
 msgstr "Включено (всегда повышать приоритет)"
 
+msgid "Enables high-capacity local DNS caching in dnsmasq to accelerate DNS queries and absorb transient latency during service restarts."
+msgstr ""
+
 msgid "Enables the background daemon that polls Telegram for commands and sends notifications."
 msgstr "Включает фоновый демон, который опрашивает Telegram на наличие команд и отправляет уведомления."
 
@@ -3095,6 +3101,9 @@ msgstr "Загрузка..."
 msgid "Local Address"
 msgstr "Локальный адрес"
 
+msgid "Local DNS Cache"
+msgstr ""
+
 msgid "Local SOCKS proxy desynchronizer (ciadpi)"
 msgstr "Локальный десинхронизатор SOCKS-прокси (ciadpi)"
 
@@ -3470,6 +3479,9 @@ msgstr "Уведомлять о перезапусках сервиса"
 msgid "Notify on Subscription Updates"
 msgstr "Уведомлять об обновлениях подписок"
 
+msgid "Number of cached DNS domain entries in dnsmasq (default: 10000)."
+msgstr ""
+
 msgid "Number of consecutive failed checks required before switching DNS servers."
 msgstr "Количество последовательных неудачных проверок до переключения DNS-серверов."