Fix TUN doctor systemd capability detection

Use the running Mihomo process capability for systemd doctor warnings while keeping the shell requirement for script backends.\n\nFixes #307

scripts/core/clashctl.sh

@@ -6597,6 +6597,23 @@ tun_recommendation_lines() {
   echo "2. 开启后建议立即执行：clash tun doctor"
 }
 
+tun_doctor_can_manage_tun_safely() {
+  local backend
+
+  tun_device_exists 2>/dev/null || return 1
+  can_manage_tun_safely 2>/dev/null && return 0
+
+  backend="$(runtime_backend 2>/dev/null || echo unknown)"
+  case "$backend" in
+    systemd|systemd-user)
+      tun_process_has_cap_net_admin "$backend" 2>/dev/null
+      ;;
+    *)
+      return 1
+      ;;
+  esac
+}
+
 tun_problem_lines() {
   local enabled env_type config_tun_enabled auto_route
   local effective_result disable_result route_dev
@@ -6628,7 +6645,7 @@ tun_problem_lines() {
     echo "• 缺少 ip 命令，无法进行完整路由校验"
   fi
 
-  if ! can_manage_tun_safely 2>/dev/null; then
+  if ! tun_doctor_can_manage_tun_safely 2>/dev/null; then
     echo "• 当前环境不满足 Tun 安全开启条件"
   fi
 

scripts/dev/check-tun-doctor-runtime-capability.sh

@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(cd "$SCRIPT_DIR/../.." && pwd)"
+
+source_clashctl_for_tests() {
+  set -- ""
+  # Source the real doctor functions; suppress the no-arg usage output.
+  source "$PROJECT_DIR/scripts/core/clashctl.sh" >/dev/null
+}
+
+source_clashctl_for_tests
+
+# Keep every unrelated doctor signal healthy so the assertion isolates the
+# capability decision reported by tun_problem_lines.
+tun_kernel_support_level() { printf 'full\n'; }
+tun_container_mode() { printf 'host\n'; }
+tun_container_risk_reason() { :; }
+status_tun_last_action_result() { :; }
+status_tun_last_action_reason() { :; }
+status_tun_last_action_time() { :; }
+tun_enabled() { printf 'true\n'; }
+container_env_type() { printf 'host\n'; }
+runtime_config_tun_enabled() { printf 'true\n'; }
+runtime_config_tun_auto_route() { printf 'true\n'; }
+default_route_dev() { printf 'Meta\n'; }
+tun_device_exists() { return 0; }
+tun_device_readable() { return 0; }
+has_ip_command() { return 0; }
+can_manage_tun_safely() { return 1; }
+runtime_config_exists() { return 0; }
+tun_current_effective_result() { printf 'ok\n'; }
+
+test_backend="systemd"
+test_process_has_cap="true"
+
+runtime_backend() { printf '%s\n' "$test_backend"; }
+tun_process_has_cap_net_admin() { [ "$test_process_has_cap" = "true" ]; }
+
+assert_capability_problem() {
+  local name="$1"
+  local expected="$2"
+  local output actual
+
+  output="$(tun_problem_lines)"
+  if printf '%s\n' "$output" | grep -Fq '当前环境不满足 Tun 安全开启条件'; then
+    actual="present"
+  else
+    actual="absent"
+  fi
+
+  if [ "$actual" != "$expected" ]; then
+    echo "not ok - $name: capability problem is $actual, expected $expected" >&2
+    [ -n "${output:-}" ] && printf '%s\n' "$output" | sed 's/^/  /' >&2
+    return 1
+  fi
+
+  echo "ok - $name"
+}
+
+# Reproduce Issue #307: a non-root diagnostic shell cannot manage Tun itself,
+# while the running systemd Mihomo process has CAP_NET_ADMIN.
+assert_capability_problem \
+  "accepts CAP_NET_ADMIN from the running systemd process" \
+  "absent"
+
+test_backend="systemd-user"
+assert_capability_problem \
+  "accepts CAP_NET_ADMIN from the running user systemd process" \
+  "absent"
+
+test_backend="systemd"
+test_process_has_cap="false"
+assert_capability_problem \
+  "keeps the warning when the systemd process lacks CAP_NET_ADMIN" \
+  "present"
+
+test_backend="script"
+test_process_has_cap="true"
+assert_capability_problem \
+  "does not borrow process capability for the script backend" \
+  "present"