fix(service): enhance message filtering to drop empty chat messages while retaining tool requests

tests/unit/test_service/test_boundary_helpers.py

@@ -74,6 +74,26 @@ def test_filter_agent_keeps_everything() -> None:
     assert [m.message_id for m in out] == ["m1", "m2"]
 
 
+def test_filter_drops_empty_plain_chat_messages_but_keeps_tool_requests() -> None:
+    msgs = [
+        _msg("m1", "user", text=""),
+        _msg("m2", "assistant", text="   "),
+        _msg(
+            "m3",
+            "assistant",
+            text="",
+            tool_calls=[ToolCall(id="tc1", function={"name": "f", "arguments": "{}"})],
+        ),
+        _msg("m4", "user", text="ok"),
+    ]
+
+    chat_out = _filter_for_mode(msgs, "chat")
+    agent_out = _filter_for_mode(msgs, "agent")
+
+    assert [m.message_id for m in chat_out] == ["m4"]
+    assert [m.message_id for m in agent_out] == ["m3", "m4"]
+
+
 # ── _to_conversation_item dispatch ────────────────────────────────────────