feat：可开启原生at功能

pytests/test_context_message_fallback.py

@@ -1,6 +1,7 @@
 from src.common.data_models.message_component_data_model import ImageComponent, MessageSequence, TextComponent
 from src.llm_models.payload_content.message import RoleType
 from src.maisaka.context_messages import _build_message_from_sequence
+from src.maisaka.message_adapter import build_visible_text_from_sequence
 
 
 def test_image_only_message_keeps_placeholder_in_text_fallback() -> None:
@@ -20,3 +21,35 @@ def test_image_only_message_keeps_placeholder_in_text_fallback() -> None:
     assert message is not None
     assert "[发言内容]" in message.get_text_content()
     assert "[图片]" in message.get_text_content()
+
+
+def test_whitespace_image_content_uses_placeholder_in_text_fallback() -> None:
+    message_sequence = MessageSequence(
+        [
+            TextComponent("[发言内容]"),
+            ImageComponent(binary_hash="hash", content="   ", binary_data=None),
+        ]
+    )
+
+    message = _build_message_from_sequence(
+        RoleType.User,
+        message_sequence,
+        "[发言内容][图片]",
+        enable_visual_message=False,
+    )
+
+    assert message is not None
+    assert message.get_text_content() == "[发言内容][图片]"
+
+
+def test_visible_text_uses_image_placeholder_for_whitespace_content() -> None:
+    visible_text = build_visible_text_from_sequence(
+        MessageSequence(
+            [
+                TextComponent("看这个"),
+                ImageComponent(binary_hash="hash", content="   ", binary_data=None),
+            ]
+        )
+    )
+
+    assert visible_text == "看这个[图片]"