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[Frontend] Merge developer instructions into tool block for Harmony prompt rendering #34951

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[Frontend] Merge developer instructions into tool block for Harmony prompt rendering #34951

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a55024e
[OpenAI] Merge system/developer instructions into the tool block for …
beom115 Feb 20, 2026
d226cf7
[Frontend] Merge system/developer instructions into the tool block fo…
beom115 Feb 20, 2026
48e842b
Merge branch 'main' into feature/harmony_chat_developer_msg
beom115 Feb 23, 2026
fcf132f
Merge branch 'main' into feature/harmony_chat_developer_msg
beom115 Feb 24, 2026
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15 changes: 12 additions & 3 deletions vllm/entrypoints/openai/chat_completion/serving.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1960,15 +1960,24 @@ def _make_request_with_harmony(
)
messages.append(sys_msg)

chat_messages = request.messages
merged_instructions: str | None = None
if chat_messages and chat_messages[0]["role"] in ("system", "developer"):
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@gemini-code-assist gemini-code-assist bot Feb 20, 2026

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high

Accessing ["role"] directly is unsafe here. ChatCompletionMessageParam is a union that includes OpenAIHarmonyMessage (a class), and even for dict-based messages, it is safer to use .get("role") to avoid potential KeyError or TypeError. Given that harmony_utils.py explicitly handles non-dict inputs, this part should be equally robust to prevent crashes if objects are passed programmatically.

content = chat_messages[0].get("content")
if isinstance(content, str):
merged_instructions = content
chat_messages = chat_messages[1:]

# Add developer message.
if request.tools:
if request.tools or merged_instructions:
dev_msg = get_developer_message(
tools=request.tools if should_include_tools else None # type: ignore[arg-type]
instructions=merged_instructions,
tools=request.tools if should_include_tools else None, # type: ignore[arg-type]
)
messages.append(dev_msg)
Comment on lines +1972 to 1977
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high

This implementation causes data loss when VLLM_GPT_OSS_HARMONY_SYSTEM_INSTRUCTIONS is enabled. The get_developer_message function in harmony_utils.py ignores the instructions argument if that environment variable is set. Since get_system_message was already called (at line 1946) without these instructions, the user-provided system/developer message content will be completely discarded from the final prompt. To fix this, the extraction logic should be moved before the get_system_message call so instructions can be passed to the appropriate block based on the environment configuration.


# Add user message.
messages.extend(parse_chat_inputs_to_harmony_messages(request.messages))
messages.extend(parse_chat_inputs_to_harmony_messages(chat_messages))

# Render prompt token ids.
prompt_token_ids = render_for_completion(messages)
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