refactor(enhance): drop unreachable mode script guard

merge_default_config overwrites the profile's mode with the verge-owned
clash config, whose mode is always present (template seeds rule and
patch semantics never clear it) and restricted to rule/global/direct;
change_clash_mode is rejected by the core before persisting anything
else. mode:script can therefore only arrive through a hand-crafted
patch_clash call, and for that path an explicit invalid-mode validation
error is more honest than silently rewriting to rule. mihomo rejects
mode:script outright (invalid mode), and user merge/script chains run
after the builtins, so the guard never covered them anyway.

src-tauri/src/enhance/chain.rs

@@ -64,10 +64,7 @@ impl ChainItem {
     /// 内建支持一些脚本
     pub fn builtin() -> Vec<Self> {
         // data intentionally empty: the enhance loop dispatches on uid to native implementations
-        vec![
-            Self::to_script("verge_hy_alpn", ""),
-            Self::to_script("verge_meta_guard", ""),
-        ]
+        vec![Self::to_script("verge_hy_alpn", "")]
     }
 
     pub fn to_script<U: Into<String>, D: Into<String>>(uid: U, data: D) -> Self {

src-tauri/src/enhance/mod.rs

@@ -610,7 +610,6 @@ fn apply_builtin_scripts(mut config: Mapping, enable_builtin: bool) -> Mapping {
             logging!(debug, Type::Core, "run builtin script {}", item.uid);
             config = match item.uid.as_str() {
                 "verge_hy_alpn" => builtin_hy_alpn(config),
-                "verge_meta_guard" => builtin_meta_guard(config),
                 _ => config,
             };
         }
@@ -633,14 +632,6 @@ fn builtin_hy_alpn(mut config: Mapping) -> Mapping {
     config
 }
 
-fn builtin_meta_guard(mut config: Mapping) -> Mapping {
-    if config.get("mode").and_then(Value::as_str) == Some("script") {
-        config.insert(Value::from("mode"), Value::from("rule"));
-    }
-
-    config
-}
-
 fn cleanup_proxy_groups(mut config: Mapping) -> Mapping {
     // built-in proxies docs: https://wiki.metacubex.one/config/proxies/built-in
     const BUILTIN_POLICIES: &[&str] = &["DIRECT", "REJECT", "REJECT-DROP", "PASS", "PASS-RULE"];