diff --git a/app/agent/prompt/__init__.py b/app/agent/prompt/__init__.py
index 3e9de3e6..6d1072ac 100644
--- a/app/agent/prompt/__init__.py
+++ b/app/agent/prompt/__init__.py
@@ -142,6 +142,7 @@ class PromptManager:
         self.prompts_cache: Dict[str, str] = {}
         self._system_tasks_cache: Optional[SystemTasksDefinition] = None
         self._system_tasks_signature: Optional[tuple[int, int]] = None
+        self._available_shell_commands_cache: Optional[list[tuple[str, str]]] = None
 
     def load_prompt(self, prompt_name: str) -> str:
         """
@@ -329,8 +330,7 @@ class PromptManager:
             sections.append(self._format_numbered_rules("IMPORTANT", rules))
         return "\n\n".join(section for section in sections if section).strip()
 
-    @staticmethod
-    def _get_moviepilot_info() -> str:
+    def _get_moviepilot_info(self) -> str:
         """
         获取MoviePilot系统信息，用于注入到系统提示词中
         """
@@ -382,7 +382,7 @@ class PromptManager:
             f"- 系统安装目录: {settings.ROOT_PATH}",
         ]
 
-        available_commands = PromptManager._get_available_shell_commands()
+        available_commands = self._get_available_shell_commands()
         if available_commands:
             info_lines.append("- 可用系统命令（可通过 `execute_command` 调用）:")
             info_lines.extend(
@@ -391,21 +391,29 @@ class PromptManager:
 
         return "\n".join(info_lines)
 
-    @staticmethod
-    def _get_available_shell_commands() -> list[tuple[str, str]]:
+    def _get_available_shell_commands(self) -> list[tuple[str, str]]:
         """
         探测 PATH 中已经安装的常用命令。
 
         这里只使用 shutil.which 做无副作用查找，不实际执行命令；执行权限、
-        高风险操作确认和输出限制仍由 execute_command 工具负责。
+        高风险操作确认和输出限制仍由 execute_command 工具负责。探测结果
+        在进程内缓存，避免每次组装提示词都重复扫描 PATH。
         """
+        if self._available_shell_commands_cache is not None:
+            return self._available_shell_commands_cache
+
         available_commands: list[tuple[str, str]] = []
         for command in COMMON_SHELL_COMMANDS:
             command_path = shutil.which(command)
             if command_path:
                 available_commands.append((command, command_path))
+        self._available_shell_commands_cache = available_commands
         return available_commands
 
+    def clear_available_shell_commands_cache(self) -> None:
+        """清理可用系统命令缓存，供测试或运行时手动刷新使用。"""
+        self._available_shell_commands_cache = None
+
     @staticmethod
     def _generate_formatting_instructions(caps: ChannelCapabilities) -> str:
         """
diff --git a/tests/test_agent_prompt_style.py b/tests/test_agent_prompt_style.py
index 10058dfd..3b32641d 100644
--- a/tests/test_agent_prompt_style.py
+++ b/tests/test_agent_prompt_style.py
@@ -3,7 +3,7 @@ from unittest.mock import patch
 
 from app.agent.middleware.memory import MEMORY_ONBOARDING_PROMPT
 from app.agent.middleware.runtime_config import RuntimeConfigMiddleware
-from app.agent.prompt import PromptConfigError, prompt_manager
+from app.agent.prompt import COMMON_SHELL_COMMANDS, PromptConfigError, prompt_manager
 from app.core.config import settings
 
 
@@ -16,6 +16,14 @@ class _FakeRequest:
 
 
 class TestAgentPromptStyle(unittest.TestCase):
+    def setUp(self):
+        """每个用例前清理系统命令缓存，避免本机 PATH 或测试顺序影响断言。"""
+        prompt_manager.clear_available_shell_commands_cache()
+
+    def tearDown(self):
+        """每个用例后清理系统命令缓存，避免 mock 探测结果泄漏到后续用例。"""
+        prompt_manager.clear_available_shell_commands_cache()
+
     def test_base_prompt_mentions_persona_management_tools(self):
         prompt = prompt_manager.get_agent_prompt()
 
@@ -62,6 +70,20 @@ class TestAgentPromptStyle(unittest.TestCase):
 
         self.assertNotIn("可用系统命令", prompt)
 
+    def test_available_shell_commands_are_cached_after_first_scan(self):
+        """常用命令探测应只在首次加载时扫描 PATH，后续提示词复用缓存。"""
+        command_paths = {"ssh": "/usr/bin/ssh"}
+        with patch(
+            "app.agent.prompt.shutil.which",
+            side_effect=lambda command: command_paths.get(command),
+        ) as which_mock:
+            first_prompt = prompt_manager.get_agent_prompt()
+            second_prompt = prompt_manager.get_agent_prompt()
+
+        self.assertIn("  - ssh: /usr/bin/ssh", first_prompt)
+        self.assertIn("  - ssh: /usr/bin/ssh", second_prompt)
+        self.assertEqual(which_mock.call_count, len(COMMON_SHELL_COMMANDS))
+
     def test_runtime_config_middleware_injects_persona_only(self):
         middleware = RuntimeConfigMiddleware()
         updated_request = middleware.modify_request(_FakeRequest())