vllm.parser ¶

class DelegatingParser(Parser):
    """
    A Parser implementation that delegates to separate ReasoningParser and
    ToolParser instances.

    This is the recommended base class for creating model-specific parsers
    that combine existing reasoning and tool parser implementations.
    Subclasses should set `self._reasoning_parser` and `self._tool_parser`
    in their `__init__` method.

    If either parser is None, the corresponding methods will return default
    values (no reasoning extraction, no tool calls).
    """

    def extract_reasoning(
        self,
        model_output: str,
        request: ChatCompletionRequest | ResponsesRequest,
    ) -> tuple[str | None, str | None]:
        if self._reasoning_parser is None:
            return None, model_output
        return self._reasoning_parser.extract_reasoning(model_output, request)

    def _get_function_name(
        self, request: ChatCompletionRequest | ResponsesRequest
    ) -> str:
        if request.tool_choice and isinstance(request.tool_choice, ToolChoiceFunction):
            return request.tool_choice.name
        if request.tool_choice and isinstance(
            request.tool_choice, ChatCompletionNamedToolChoiceParam
        ):
            return request.tool_choice.function.name
        raise ValueError("Invalid tool_choice for function name extraction.")

    def _make_tool_call_id(self, function_name: str) -> str | None:
        state = self._stream_state
        if state.tool_call_id_type != "kimi_k2":
            return None
        tool_call_id = make_tool_call_id(
            id_type=state.tool_call_id_type,
            func_name=function_name,
            idx=state.history_tool_call_cnt,
        )
        state.history_tool_call_cnt += 1
        return tool_call_id

    def _extract_tool_calls(
        self,
        content: str | None,
        request: ChatCompletionRequest | ResponsesRequest,
        enable_auto_tools: bool = False,
    ) -> tuple[list[FunctionCall] | None, str | None]:
        tool_parser = self._tool_parser
        if tool_parser is None:
            return [], content

        if request.tool_choice == "none":
            if self._engine_based:
                result = self.extract_tool_calls(content or "", request=request)
                return [], result.content
            return [], content

        supports_required_and_named = tool_parser.supports_required_and_named
        is_named_tool_choice = request.tool_choice and isinstance(
            request.tool_choice,
            (ToolChoiceFunction, ChatCompletionNamedToolChoiceParam),
        )
        is_required_tool_choice = request.tool_choice == "required"
        is_auto_tool_choice = enable_auto_tools and (
            request.tool_choice == "auto"
            or request.tool_choice is None
            or (
                not supports_required_and_named
                and (is_named_tool_choice or is_required_tool_choice)
            )
        )

        tool_calls = list[FunctionCall]()
        if is_named_tool_choice and supports_required_and_named:
            if content is None or (isinstance(content, str) and not content.strip()):
                return [], None
            function_name = self._get_function_name(request)
            tool_calls.append(
                FunctionCall(
                    id=self._make_tool_call_id(function_name),
                    name=function_name,
                    arguments=content,
                )
            )
            content = None
        elif is_required_tool_choice and supports_required_and_named:
            # "required" with standard JSON-based parsing
            parsed_calls = []
            with contextlib.suppress(ValidationError):
                content = content or ""
                parsed_calls = TypeAdapter(list[FunctionDefinition]).validate_json(
                    content
                )
            for tc in parsed_calls:
                tool_calls.append(
                    FunctionCall(
                        id=self._make_tool_call_id(tc.name),
                        name=tc.name,
                        arguments=json.dumps(tc.parameters, ensure_ascii=False),
                    )
                )
            content = None
        elif is_auto_tool_choice:
            # Automatic Tool Call Parsing (also used as fallback for
            # required/named when supports_required_and_named=False)
            tool_call_info = self.extract_tool_calls(
                content if content is not None else "",
                request=request,
            )
            if tool_call_info is not None and tool_call_info.tools_called:
                tool_calls.extend(
                    FunctionCall(
                        id=tc.id,
                        name=tc.function.name,
                        arguments=tc.function.arguments,
                    )
                    for tc in tool_call_info.tool_calls
                )
                content = tool_call_info.content
                if content and content.strip() == "":
                    content = None
            else:
                # No tool calls.
                # For required/named tool choice (when falling back to auto
                # parsing), if content is empty or whitespace-only, return
                # empty list with None content.
                if (is_required_tool_choice or is_named_tool_choice) and (
                    content is None
                    or (isinstance(content, str) and not content.strip())
                ):
                    return [], None
                # No complete tool calls: for engine-based parsers, return
                # the tool parser's content, which drops incomplete
                # tool-call markup (e.g. a <tool_call> opener truncated by
                # max_tokens or a stop string), so the non-streaming path
                # matches streaming. Legacy parsers keep their existing
                # behavior of returning the raw content.
                if self._engine_based and tool_call_info is not None:
                    return None, tool_call_info.content or None
                return None, content

        return tool_calls, content

    def adjust_request(
        self, request: ChatCompletionRequest | ResponsesRequest
    ) -> ChatCompletionRequest | ResponsesRequest:
        if self._reasoning_parser is not None:
            request = self._reasoning_parser.adjust_request(request)
        if self._tool_parser is not None:
            request = self._apply_structural_tag(request)
        if self._tool_parser is not None:
            request = self._tool_parser.adjust_request(request)
        return request

    def _apply_structural_tag(
        self, request: ChatCompletionRequest | ResponsesRequest
    ) -> ChatCompletionRequest | ResponsesRequest:
        if (
            self._tool_parser is None
            or self._tool_parser.structural_tag_model is None
            or not request.tools
        ):
            return request

        need_tool_calling = (
            request.tool_choice == "auto"
            or request.tool_choice == "required"
            or isinstance(
                request.tool_choice,
                (ChatCompletionNamedToolChoiceParam, ToolChoiceFunction),
            )
        )
        if not need_tool_calling:
            return request

        structure_tag = self._tool_parser.get_structural_tag(
            request,
            reasoning=False,
        )
        if structure_tag is None:
            return request

        structural_tag = json.dumps(structure_tag.model_dump())
        request.structured_outputs = StructuredOutputsParams(
            structural_tag=structural_tag,
        )
        if isinstance(request, ResponsesRequest):
            request.text = None
        else:
            request.response_format = None
        return request

    def extract_reasoning_streaming(
        self,
        previous_text: str,
        current_text: str,
        delta_text: str,
        previous_token_ids: Sequence[int],
        current_token_ids: Sequence[int],
        delta_token_ids: Sequence[int],
    ) -> DeltaMessage | None:
        if self._reasoning_parser is None:
            return DeltaMessage(content=delta_text)
        return self._reasoning_parser.extract_reasoning_streaming(
            previous_text,
            current_text,
            delta_text,
            previous_token_ids,
            current_token_ids,
            delta_token_ids,
        )

    def extract_tool_calls(
        self,
        model_output: str,
        request: ChatCompletionRequest | ResponsesRequest,
    ) -> ExtractedToolCallInformation:
        if self._tool_parser is None:
            return ExtractedToolCallInformation(
                tools_called=False, tool_calls=[], content=model_output
            )
        result = None
        is_tool_called: bool | Exception = False
        try:
            result = self._tool_parser.extract_tool_calls(
                model_output,
                request=request,  # type: ignore[arg-type]
            )
            is_tool_called = bool(result.tools_called)
        except Exception as e:
            is_tool_called = e
            raise
        finally:
            record_tool_parser_invocation(
                is_tool_called=is_tool_called,
                is_streaming=False,
                request=request,
            )
        return result

    def extract_tool_calls_streaming(
        self,
        previous_text: str,
        current_text: str,
        delta_text: str,
        previous_token_ids: Sequence[int],
        current_token_ids: Sequence[int],
        delta_token_ids: Sequence[int],
        request: ChatCompletionRequest | ResponsesRequest,
    ) -> DeltaMessage | None:
        if self._tool_parser is None:
            return None
        result = None
        is_tool_called: bool | Exception = False
        try:
            result = self._tool_parser.extract_tool_calls_streaming(
                previous_text,
                current_text,
                delta_text,
                previous_token_ids,
                current_token_ids,
                delta_token_ids,
                request,  # type: ignore[arg-type]
            )
            is_tool_called = bool(result and result.tool_calls)
        except Exception as e:
            is_tool_called = e
            raise
        finally:
            record_tool_parser_invocation(
                is_tool_called=is_tool_called,
                is_streaming=True,
                request=request,
            )
        return result

    def _extract_tool_calls_streaming(
        self,
        previous_text: str,
        current_text: str,
        delta_text: str,
        previous_token_ids: Sequence[int],
        current_token_ids: Sequence[int],
        delta_token_ids: Sequence[int],
        request: ChatCompletionRequest | ResponsesRequest,
        # The following parameters are used for "required" tool choice parsing and are
        # tracked in StreamState for streaming parsing.
        tool_call_idx: int | None = None,
        tool_call_id_type: str = "random",
        function_name_returned: bool = False,
    ) -> tuple[DeltaMessage | None, bool]:
        assert self._tool_parser is not None
        supports_required_and_named = self._tool_parser.supports_required_and_named

        if request.tool_choice == "none":
            if self._engine_based:
                # Engine-backed parsers route content extraction through
                # extract_tool_calls_streaming, so run the full pipeline
                # and strip tool_calls after.
                delta_message = self.extract_tool_calls_streaming(
                    previous_text,
                    current_text,
                    delta_text,
                    previous_token_ids,
                    current_token_ids,
                    delta_token_ids,
                    request,  # type: ignore[arg-type]
                )
                if delta_message:
                    delta_message.tool_calls = []
                return delta_message, False
            return (DeltaMessage(content=delta_text) if delta_text else None), False

        if (
            supports_required_and_named
            and request.tool_choice
            and isinstance(
                request.tool_choice,
                (ToolChoiceFunction, ChatCompletionNamedToolChoiceParam),
            )
        ):
            delta_message, function_name_returned = extract_named_tool_call_streaming(
                delta_text=delta_text,
                function_name=self._get_function_name(request),
                function_name_returned=function_name_returned,
                tool_call_idx=tool_call_idx,
                tool_call_id_type=tool_call_id_type,
                tokenizer=self.model_tokenizer,
            )
            return delta_message, function_name_returned

        if supports_required_and_named and request.tool_choice == "required":
            delta_message, function_name_returned = (
                extract_required_tool_call_streaming(
                    previous_text=previous_text,
                    current_text=current_text,
                    delta_text=delta_text,
                    function_name_returned=function_name_returned,
                    tool_call_idx=tool_call_idx,
                    tool_call_id_type=tool_call_id_type,
                )
            )
            return delta_message, function_name_returned
        return self.extract_tool_calls_streaming(
            previous_text,
            current_text,
            delta_text,
            previous_token_ids,
            current_token_ids,
            delta_token_ids,
            request,
        ), False

    def is_reasoning_end(self, input_ids: list[int]) -> bool:
        if self._reasoning_parser is None:
            return False
        return self._reasoning_parser.is_reasoning_end(input_ids)

    def is_reasoning_end_streaming(
        self, input_ids: list[int], delta_ids: list[int]
    ) -> bool:
        if self._reasoning_parser is None:
            return False
        return self._reasoning_parser.is_reasoning_end_streaming(input_ids, delta_ids)

    def extract_content_ids(self, input_ids: list[int]) -> list[int]:
        if self._reasoning_parser is None:
            return input_ids
        return self._reasoning_parser.extract_content_ids(input_ids)

    def _in_reasoning_phase(self, state: StreamState) -> bool:
        if self._reasoning_parser is None:
            return False
        return not state.reasoning_ended

    def _in_tool_call_phase(self, state: StreamState) -> bool:
        if self._tool_parser is None:
            return False
        return state.reasoning_ended

    def _append_unstreamed_tool_args(
        self,
        delta_message: DeltaMessage | None,
    ) -> None:
        """Append parsed-but-unstreamed tool-call arguments to *delta_message*."""
        if (
            self._tool_parser is not None
            and delta_message
            and delta_message.tool_calls
            and (last_tc := delta_message.tool_calls[-1]).function
        ):
            last_tc.function.arguments = (
                last_tc.function.arguments or ""
            ) + self._tool_parser.get_remaining_unstreamed_args()

    def finalize_generation(
        self,
        delta_message: DeltaMessage | None,
        request: ChatCompletionRequest | ResponsesRequest,
        state: StreamState,
    ) -> DeltaMessage | None:
        """Finalize generation for cases where generation was incomplete.
        For example, if streaming terminated before reasoning ended
        """
        fallback_fn = getattr(
            self._reasoning_parser, "get_streaming_fallback_content", None
        )
        if fallback_fn is not None and not state.reasoning_ended:
            promoted = fallback_fn(state.previous_text, request)
            if promoted:
                if delta_message is None:
                    delta_message = DeltaMessage()
                delta_message.content = (delta_message.content or "") + promoted

        self._append_unstreamed_tool_args(delta_message)
        return delta_message

    def parse(
        self,
        model_output: str,
        request: ChatCompletionRequest | ResponsesRequest,
        enable_auto_tools: bool = False,
        model_output_token_ids: Sequence[int] = (),
    ) -> tuple[str | None, str | None, list[FunctionCall] | None]:
        self._initialize_history_tool_call_cnt(request)
        reasoning, content = self.extract_reasoning(model_output, request)
        tool_calls, content = self._extract_tool_calls(
            content=content,
            request=request,
            enable_auto_tools=enable_auto_tools,
        )
        return reasoning, content, tool_calls

    def parse_delta(
        self,
        delta_text: str,
        delta_token_ids: list[int],
        request: ChatCompletionRequest | ResponsesRequest,
        prompt_token_ids: list[int] | None = None,
        *,
        finished: bool,
    ) -> DeltaMessage | None:
        self._initialize_history_tool_call_cnt(request)
        state = self._stream_state

        if not state.prompt_reasoning_checked and prompt_token_ids is not None:
            state.prompt_reasoning_checked = True
            if self._reasoning_parser is None or self.is_reasoning_end(
                prompt_token_ids
            ):
                state.reasoning_ended = True
            else:
                # Reasoning is still open at the end of the prompt; let the
                # reasoning parser adjust its initial parsing state so the
                # first generated tokens are classified correctly.
                self._reasoning_parser.adjust_initial_state_from_prompt(
                    prompt_token_ids
                )

        current_text, current_token_ids = state.advance(delta_text, delta_token_ids)
        delta_message: DeltaMessage | None = None
        reasoning_transitioned = False

        # Reasoning extraction
        if self._in_reasoning_phase(state):
            delta_message = self.extract_reasoning_streaming(
                previous_text=state.previous_text,
                current_text=current_text,
                delta_text=delta_text,
                previous_token_ids=state.previous_token_ids,
                current_token_ids=current_token_ids,
                delta_token_ids=delta_token_ids,
            )
            reasoning_parser = self._reasoning_parser
            if reasoning_parser is not None and reasoning_parser.engine_based_streaming:
                should_transition = (
                    reasoning_parser.has_engine_confirmed_reasoning_end()
                )
            else:
                should_transition = self.is_reasoning_end_streaming(
                    current_token_ids, delta_token_ids
                )
            if should_transition:
                state.reasoning_ended = True
                reasoning_transitioned = True
                current_token_ids = self.extract_content_ids(delta_token_ids)
                # Flush whenever the reasoning parser is engine-based (not only
                # when _engine_based is True): it buffers the post-marker text
                # (e.g. the "<" of "<tool_call>"), surfaced via finish_streaming().
                flush_delta = (
                    reasoning_parser.finish_streaming()  # type: ignore[union-attr, attr-defined]
                    if reasoning_parser is not None
                    and reasoning_parser.engine_based_streaming
                    else None
                )
                current_text = (
                    (delta_message.content if delta_message else None) or ""
                ) + ((flush_delta.content if flush_delta else None) or "")
                if self._engine_based:
                    if delta_message and self._tool_parser is not None:
                        delta_message.content = None
                else:
                    delta_text = current_text

        # Tool call extraction
        if self._in_tool_call_phase(state):
            if not state.tool_call_text_started:
                state.tool_call_text_started = True
                state.previous_text = ""
                state.previous_token_ids = []
                delta_text = current_text
                delta_token_ids = current_token_ids

            reasoning_from_this_batch = (
                delta_message.reasoning if delta_message else None
            )

            delta_message, state.function_name_returned = (
                self._extract_tool_calls_streaming(
                    previous_text=state.previous_text,
                    current_text=current_text,
                    delta_text=delta_text,
                    previous_token_ids=state.previous_token_ids,
                    current_token_ids=current_token_ids,
                    delta_token_ids=delta_token_ids,
                    request=request,  # type: ignore[arg-type]
                    tool_call_idx=state.history_tool_call_cnt,
                    tool_call_id_type=state.tool_call_id_type,
                    function_name_returned=state.function_name_returned,
                )
            )

            if reasoning_from_this_batch:
                if delta_message is None:
                    delta_message = DeltaMessage(reasoning=reasoning_from_this_batch)
                elif not delta_message.reasoning:
                    delta_message.reasoning = reasoning_from_this_batch

            if (
                delta_message
                and delta_message.tool_calls
                and delta_message.tool_calls[0].id is not None
            ):
                state.history_tool_call_cnt += 1

        # No phase active: pass through as content.
        # Skip when reasoning just ended in this delta — the engine already
        # consumed the end-of-reasoning marker (e.g. </think>) and
        # delta_text still contains the raw marker text.
        if (
            delta_message is None
            and not reasoning_transitioned
            and not self._in_reasoning_phase(state)
            and not self._in_tool_call_phase(state)
        ):
            delta_message = DeltaMessage(content=delta_text)

        state.commit(current_text, current_token_ids)

        if finished:
            delta_message = self.finalize_generation(delta_message, request, state)
            delta_message = self._flush_engine_parsers(delta_message)

        # Suppress reasoning deltas if not requested
        if delta_message and not request.include_reasoning:
            delta_message.reasoning = None

            # If only reasoning was in the message (no content, no tool_calls)
            # skip emitting entirely
            if not delta_message.content and not delta_message.tool_calls:
                delta_message = None

        return delta_message

    def count_reasoning_tokens(self, token_ids: Sequence[int]) -> int:
        """Count reasoning tokens through the configured reasoning parser."""
        if self._reasoning_parser is None:
            return 0
        return self._reasoning_parser.count_reasoning_tokens(token_ids)

    def _flush_engine_parsers(
        self, delta_message: DeltaMessage | None
    ) -> DeltaMessage | None:
        """Flush buffered state from engine-based parsers at stream end."""
        reasoning_ended = self._stream_state.reasoning_ended
        for parser in (self._reasoning_parser, self._tool_parser):
            if not getattr(parser, "engine_based_streaming", False):
                continue
            # When reasoning has ended and we transitioned to the tool
            # phase, the reasoning parser's engine may still have buffered
            # characters from tool-call markup it saw with
            # skip_tool_parsing=True.  Flushing that would leak spurious
            # content (e.g. a stray '"'), so skip it.
            if parser is self._reasoning_parser and reasoning_ended:
                continue
            finish = getattr(parser, "finish_streaming", None)
            if finish is None:
                continue
            flush_delta = finish()
            if flush_delta is None:
                continue
            if delta_message is None:
                delta_message = flush_delta
            else:
                if flush_delta.content:
                    delta_message.content = (
                        delta_message.content or ""
                    ) + flush_delta.content
                if flush_delta.reasoning:
                    delta_message.reasoning = (
                        delta_message.reasoning or ""
                    ) + flush_delta.reasoning
                if flush_delta.tool_calls:
                    delta_message.tool_calls = (
                        delta_message.tool_calls or []
                    ) + flush_delta.tool_calls
        return delta_message

class HarmonyParser(DelegatingParser):
    def __init__(self, tokenizer, tools=None, *args, **kwargs):
        super().__init__(tokenizer, tools, *args, **kwargs)

        if self.reasoning_parser and not isinstance(
            self.reasoning_parser, GptOssReasoningParser
        ):
            raise ValueError(
                "Harmony requires GptOssReasoningParser, "
                f"got {self.reasoning_parser.__class__.__name__}."
            )

        if self.tool_parser and not isinstance(self.tool_parser, GptOssToolParser):
            raise ValueError(
                "Harmony requires GptOssToolParser, "
                f"got {self.tool_parser.__class__.__name__}."
            )

        self._parser: StreamableParser | None = None
        self._next_tool_call_index = 0
        self._num_processed_messages = 0

        # For error recovery
        self._current_message_tokens: list[int] = []

    @property
    def _harmony_parser(self) -> StreamableParser:
        """Lazily initializes the Harmony parser."""
        if self._parser is None:
            self._parser = get_streamable_parser_for_assistant()
        return self._parser

    def _poll_completed_message(self) -> Message | None:
        messages = self._harmony_parser.messages
        if len(messages) <= self._num_processed_messages:
            return None
        msg = messages[self._num_processed_messages]
        msg.recipient = self._normalize_recipient(msg.recipient)
        self._num_processed_messages += 1
        return msg

    def flush(self) -> list[Segment]:
        segments: list[Segment] = []
        try:
            self._harmony_parser.process_eos()
            msg = self._poll_completed_message()
        except HarmonyError:
            logger.warning(
                "Harmony parser ended in a non-terminal state; returning the "
                "recovered raw output."
            )

            final_channel = "final"
            text = self.model_tokenizer.decode(self._current_message_tokens)
            segments.append(
                Segment(
                    channel=final_channel,
                    recipient=None,
                    delta=text,
                    completed_message=None,
                )
            )
            msg = Message.from_role_and_content(Role.ASSISTANT, text).with_channel(
                final_channel
            )

        # Reset to the initial assistant-parser state for the next turn.
        self._parser = None
        self._num_processed_messages = 0
        self._current_message_tokens.clear()

        if msg is None:
            return segments

        segments.append(
            Segment(
                channel=msg.channel,
                recipient=msg.recipient,
                delta="",
                completed_message=msg,
            )
        )
        return segments

    def parse(
        self,
        model_output: str,
        request: ChatCompletionRequest | ResponsesRequest,
        enable_auto_tools: bool = False,
        model_output_token_ids: Sequence[int] = (),
    ) -> tuple[str | None, str | None, list[FunctionCall] | None]:
        """Parse Harmony output from token IDs.

        Tool calls are always extracted regardless of ``enable_auto_tools``.
        Callers must decide whether to surface them.
        """
        result = self.process_chunk(model_output_token_ids)
        flushed_segments = self.flush()
        if flushed_segments:
            result.segments.extend(flushed_segments)

        reasoning_parts: list[str] = []
        content_parts: list[str] = []
        tool_calls: list[FunctionCall] = []

        for segment in result.segments:
            msg = segment.completed_message
            if msg is None:
                continue
            if msg.author.role != "assistant" or not msg.content:
                continue
            text = msg.content[0].text
            segment_type = _SegmentType.from_channel_and_recipient(
                msg.channel, msg.recipient
            )
            match segment_type:
                case _SegmentType.REASONING if self.reasoning_parser and text:
                    reasoning_parts.append(text)
                case _SegmentType.CONTENT if text:
                    content_parts.append(text)
                case _SegmentType.TOOL if self.tool_parser:
                    recipient = msg.recipient
                    content_type = msg.content_type
                    assert recipient is not None
                    if content_type is not None and "json" not in content_type:
                        arguments = text
                    else:
                        try:
                            arguments = json.dumps(json.loads(text))
                        except json.JSONDecodeError:
                            arguments = text
                    tool_calls.append(
                        FunctionCall(
                            name=extract_function_from_recipient(recipient),
                            arguments=arguments,
                        )
                    )

        reasoning = "\n".join(reasoning_parts) or None
        content = "\n".join(content_parts) or None
        return reasoning, content, tool_calls or None

    def parse_delta(
        self,
        delta_text: str,
        delta_token_ids: list[int],
        request: ChatCompletionRequest | ResponsesRequest,
        prompt_token_ids: list[int] | None = None,
        *,
        finished: bool,
    ) -> DeltaMessage | None:
        prev_recipient = self._normalize_recipient(
            self._harmony_parser.current_recipient
        )
        result = self.process_chunk(delta_token_ids)
        if finished:
            flushed_segments = self.flush()
            if flushed_segments:
                result.segments.extend(flushed_segments)
        combined_content = ""
        combined_reasoning = ""
        tool_messages: list[DeltaToolCall] = []

        for segment in result.segments:
            if segment.completed_message is not None:
                prev_recipient = None
                continue

            segment_type = _SegmentType.from_channel_and_recipient(
                segment.channel, segment.recipient
            )
            match segment_type:
                case _SegmentType.REASONING if self.reasoning_parser:
                    combined_reasoning += segment.delta
                case _SegmentType.CONTENT:
                    combined_content += segment.delta
                case _SegmentType.TOOL if self.tool_parser:
                    assert segment.recipient is not None
                    if prev_recipient != segment.recipient:
                        tool_name = extract_function_from_recipient(segment.recipient)
                        tool_messages.append(
                            DeltaToolCall(
                                # HarmonyParser does not use _stream_state;
                                # "random" tool_call_id_type is always used
                                id=make_tool_call_id(),
                                type="function",
                                function=DeltaFunctionCall(
                                    name=tool_name,
                                    arguments=segment.delta,
                                ),
                                index=self._next_tool_call_index,
                            )
                        )
                        self._next_tool_call_index += 1
                        prev_recipient = segment.recipient
                    elif segment.delta:
                        idx = self._next_tool_call_index - 1
                        if tool_messages:
                            tool_msg = tool_messages[-1]
                            assert tool_msg.index == idx
                            fn = tool_msg.function
                            assert fn is not None and fn.arguments is not None
                            fn.arguments += segment.delta
                        else:
                            tool_messages.append(
                                DeltaToolCall(
                                    index=idx,
                                    function=DeltaFunctionCall(arguments=segment.delta),
                                )
                            )

        if finished:
            self._next_tool_call_index = 0

        if not combined_content and not combined_reasoning and not tool_messages:
            return None

        delta_message = DeltaMessage()
        if combined_content:
            delta_message.content = combined_content
        if combined_reasoning:
            delta_message.reasoning = combined_reasoning
        if tool_messages:
            delta_message.tool_calls = tool_messages

        # Suppress reasoning deltas if not requested
        if delta_message and not request.include_reasoning:
            delta_message.reasoning = None

            # If only reasoning was in the message (no content, no tool_calls)
            # skip emitting entirely
            if not delta_message.content and not delta_message.tool_calls:
                return None

        return delta_message

    def process_chunk(self, token_ids: Sequence[int]) -> ChunkResult:
        if not token_ids:
            return ChunkResult(segments=[], reasoning_token_count=0)

        segments: list[Segment] = []
        reasoning_token_count = 0
        for token_id in token_ids:
            self._harmony_parser.process(token_id)
            channel = self._harmony_parser.current_channel
            recipient = self._normalize_recipient(
                self._harmony_parser.current_recipient
            )
            delta = self._harmony_parser.last_content_delta or ""
            completed_message = self._poll_completed_message()

            if completed_message is not None:
                self._current_message_tokens.clear()
            else:
                self._current_message_tokens.append(token_id)

            if channel == "analysis" or (
                channel == "commentary" and recipient is not None
            ):
                reasoning_token_count += 1

            segments.append(
                Segment(
                    channel=channel,
                    recipient=recipient,
                    delta=delta,
                    completed_message=completed_message,
                )
            )

            # TODO: Optionally merge and suppress empty Segments

        return ChunkResult(
            segments=segments,
            reasoning_token_count=reasoning_token_count,
        )

    def adjust_request(
        self, request: ChatCompletionRequest | ResponsesRequest
    ) -> ChatCompletionRequest | ResponsesRequest:
        request = _adjust_output_format(request)
        return super().adjust_request(request)

    @staticmethod
    def _normalize_recipient(recipient: str | None) -> str | None:
        """Remove constrained formats misparsed into recipients by older Harmony."""
        if recipient is None:
            return None

        constrain_index = recipient.find("<|constrain|>")
        if constrain_index == -1:
            return recipient
        return recipient[:constrain_index].rstrip() or None