diff --git a/astrbot/core/skills/skill_manager.py b/astrbot/core/skills/skill_manager.py
index 03ba1e153e..0b51529d2e 100644
--- a/astrbot/core/skills/skill_manager.py
+++ b/astrbot/core/skills/skill_manager.py
@@ -681,6 +681,8 @@ def list_skills(
         return [skills_by_name[name] for name in sorted(skills_by_name)]
 
     def is_sandbox_only_skill(self, name: str) -> bool:
+        if self._get_plugin_skill_dir(name) is not None:
+            return False
         skill_dir = Path(self.skills_root) / name
         skill_md_exists = _normalize_skill_markdown_path(skill_dir) is not None
         if skill_md_exists:
diff --git a/tests/test_skill_manager_sandbox_cache.py b/tests/test_skill_manager_sandbox_cache.py
index 1af5d2f213..3ad1372432 100644
--- a/tests/test_skill_manager_sandbox_cache.py
+++ b/tests/test_skill_manager_sandbox_cache.py
@@ -170,3 +170,42 @@ def test_sandbox_and_local_path_resolution_with_show_sandbox_path_false(
     assert local_skill_path.is_relative_to(skills_root)
     assert local_skill_path == skills_root / "custom-local" / "SKILL.md"
     assert by_name["python-sandbox"].path == "/app/skills/python-sandbox/SKILL.md"
+
+
+def test_plugin_skill_with_stale_sandbox_cache_is_not_sandbox_only(
+    monkeypatch,
+    tmp_path: Path,
+):
+    data_dir = tmp_path / "data"
+    temp_dir = tmp_path / "temp"
+    skills_root = tmp_path / "skills"
+    data_dir.mkdir(parents=True, exist_ok=True)
+    temp_dir.mkdir(parents=True, exist_ok=True)
+    skills_root.mkdir(parents=True, exist_ok=True)
+
+    monkeypatch.setattr(
+        "astrbot.core.skills.skill_manager.get_astrbot_data_path",
+        lambda: str(data_dir),
+    )
+    monkeypatch.setattr(
+        "astrbot.core.skills.skill_manager.get_astrbot_temp_path",
+        lambda: str(temp_dir),
+    )
+
+    from astrbot.core.skills import skill_manager as skill_manager_module
+
+    plugin_skills_root = Path(skill_manager_module.get_astrbot_plugin_path())
+    _write_skill(plugin_skills_root / "astrbot" / "skills", "pdf", "builtin pdf")
+
+    mgr = SkillManager(skills_root=str(skills_root))
+    mgr.set_sandbox_skills_cache(
+        [
+            {
+                "name": "pdf",
+                "description": "stale sandbox cache entry",
+                "path": "/app/skills/pdf/SKILL.md",
+            }
+        ]
+    )
+
+    assert mgr.is_sandbox_only_skill("pdf") is False