diff --git a/ai-service-admin/src/types/prompt-template.ts b/ai-service-admin/src/types/prompt-template.ts
index f59450e..4ab79ee 100644
--- a/ai-service-admin/src/types/prompt-template.ts
+++ b/ai-service-admin/src/types/prompt-template.ts
@@ -85,6 +85,7 @@ export const SCENE_OPTIONS = [
   { value: 'summary', label: '摘要场景' },
   { value: 'translation', label: '翻译场景' },
   { value: 'code', label: '代码场景' },
+  { value: 'agent_react', label: 'Agent ReAct 场景' },
   { value: 'custom', label: '自定义场景' }
 ]
 
@@ -98,5 +99,6 @@ export const BUILTIN_VARIABLES: PromptVariable[] = [
   { name: 'user_name', description: '用户名称' },
   { name: 'context', description: '检索上下文' },
   { name: 'query', description: '用户问题' },
-  { name: 'history', description: '对话历史' }
+  { name: 'history', description: '对话历史' },
+  { name: 'available_tools', description: '可用工具列表（Agent ReAct 场景专用，自动注入已注册工具的名称、描述和参数）' }
 ]
diff --git a/ai-service/app/services/prompt/variable_resolver.py b/ai-service/app/services/prompt/variable_resolver.py
index 59c8def..8b91b2c 100644
--- a/ai-service/app/services/prompt/variable_resolver.py
+++ b/ai-service/app/services/prompt/variable_resolver.py
@@ -8,6 +8,8 @@ import re
 from datetime import datetime
 from typing import Any
 
+from app.core.middleware import PROMPT_PROTECTED_VARIABLES
+
 logger = logging.getLogger(__name__)
 
 VARIABLE_PATTERN = re.compile(r"\{\{(\w+)\}\}")
@@ -18,6 +20,11 @@ BUILTIN_VARIABLES = {
     "channel_type": "default",
     "tenant_name": "平台",
     "session_id": "",
+    "available_tools": "",
+    "query": "",
+    "history": "",
+    "internal_protocol": "",
+    "output_contract": "",
 }
 
 
@@ -92,10 +99,18 @@ class VariableResolver:
             for var in variables:
                 name = var.get("name")
                 default = var.get("default", "")
-                if name:
-                    context[name] = default
+                if not name:
+                    continue
+                if name in PROMPT_PROTECTED_VARIABLES:
+                    logger.warning(
+                        "Protected prompt variable '%s' cannot be overridden by template defaults",
+                        name,
+                    )
+                    continue
+                context[name] = default
 
         if extra_context:
+            # Runtime/system context has the highest priority, including protected vars.
             context.update(extra_context)
 
         return context