fix: hf agent outputs the prompt text while the openai agent not (#5461)

* add skil prompt

* fix formatting

* add release note

* add release note

* Update releasenotes/notes/add-skip-prompt-for-hf-model-agent-89aef2838edb907c.yaml

Co-authored-by: Daria Fokina <daria.f93@gmail.com>

* Update haystack/nodes/prompt/invocation_layer/handlers.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update haystack/nodes/prompt/invocation_layer/handlers.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update haystack/nodes/prompt/invocation_layer/hugging_face.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* add a unit test

* add a unit test2

* add skil prompt

* Revert "add skil prompt"

This reverts commit b1ba938c94b67a4fd636d321945990aabd2c5b2a.

* add unit test

---------

Co-authored-by: Daria Fokina <daria.f93@gmail.com>
Co-authored-by: bogdankostic <bogdankostic@web.de>

haystack/nodes/prompt/invocation_layer/handlers.py

@@ -47,7 +47,7 @@ class HFTokenStreamingHandler(TextStreamer):  # pylint: disable=useless-object-i
         stream_handler: "TokenStreamingHandler",
     ):
         transformers_import.check()
-        super().__init__(tokenizer=tokenizer)  # type: ignore
+        super().__init__(tokenizer=tokenizer, skip_prompt=True)  # type: ignore
         self.token_handler = stream_handler
 
     def on_finalized_text(self, token: str, stream_end: bool = False):

releasenotes/notes/add-skip-prompt-for-hf-model-agent-89aef2838edb907c.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fix the bug that the responses of Agents using local HF models contain the prompt text.

test/prompt/invocation_layer/test_hugging_face.py

@@ -632,3 +632,17 @@ def test_tokenizer_loading_unsupported_model_with_tokenizer_class_in_config(
         invocation_layer = HFLocalInvocationLayer(model_name_or_path="unsupported_model", trust_remote_code=True)
         assert not mock_tokenizer.called
         assert not caplog.text
+
+
+@pytest.mark.unit
+def test_skip_prompt_is_set_in_hf_text_streamer(mock_pipeline, mock_get_task):
+    """
+    Test that skip_prompt is set in HFTextStreamingHandler. Otherwise, we will output prompt text.
+    """
+    layer = HFLocalInvocationLayer(stream=True)
+
+    layer.invoke(prompt="Tell me hello")
+
+    _, kwargs = layer.pipe.call_args
+    assert "streamer" in kwargs and isinstance(kwargs["streamer"], HFTokenStreamingHandler)
+    assert kwargs["streamer"].skip_prompt