fix: update the tool calling functionalities for sglang frontend processor to...

fix: update the tool calling functionalities for sglang frontend processor to match with the latest sglang implementation (#8269)

components/src/dynamo/frontend/frontend_args.py

@@ -86,6 +86,7 @@ class FrontendConfig(KvRouterConfigBase, AicPerfConfigBase):
     exclude_tools_when_tool_choice_none: bool
     preprocess_workers: int
     tokenizer_backend: str
+    trust_remote_code: bool
 
     _VALID_TOKENIZER_BACKENDS = {"default", "fastokens"}
 
@@ -562,3 +563,14 @@ class FrontendArgGroup(ArgGroup):
             ),
             choices=["default", "fastokens"],
         )
+
+        add_negatable_bool_argument(
+            g,
+            flag_name="--trust-remote-code",
+            env_var="DYN_TRUST_REMOTE_CODE",
+            default=False,
+            help=(
+                "Trust remote code when loading the tokenizer. Required for models "
+                "that ship custom tokenizer code (e.g. Qwen, Falcon)."
+            ),
+        )

components/src/dynamo/frontend/main.py

@@ -114,17 +114,6 @@ def parse_args() -> tuple[FrontendConfig, Optional[Namespace], Optional[Namespac
     vllm_flags = None
     sglang_flags = None
 
-    # --trust-remote-code is only meaningful with --dyn-chat-processor vllm.
-    # Warn and strip it when a different (or no) chat processor is active so
-    # it does not propagate as an unknown-argument error below.
-    if "--trust-remote-code" in unknown and config.chat_processor != "vllm":
-        logger.warning(
-            "--trust-remote-code has no effect without '--dyn-chat-processor vllm'. "
-            "It is only supported by the vLLM chat processor. "
-            "Pass '--dyn-chat-processor vllm' to enable trust_remote_code."
-        )
-        unknown = [arg for arg in unknown if arg != "--trust-remote-code"]
-
     # parse extra vllm flags using vllm native parser.
     if config.chat_processor == "vllm":
         try:

components/src/dynamo/frontend/sglang_prepost.py

@@ -3,24 +3,42 @@
 
 from __future__ import annotations
 
+import json
+import logging
 from dataclasses import dataclass
-from typing import Any
+from typing import Any, TypeAlias
 
 from sglang.srt.entrypoints.openai.protocol import Function as SglangFunction
 from sglang.srt.entrypoints.openai.protocol import Tool as SglangTool
+from sglang.srt.entrypoints.openai.protocol import ToolChoice as SglangToolChoice
+from sglang.srt.entrypoints.openai.protocol import (
+    ToolChoiceFuncName as SglangToolChoiceFuncName,
+)
+from sglang.srt.function_call.core_types import ToolCallItem
 from sglang.srt.function_call.function_call_parser import FunctionCallParser
+from sglang.srt.function_call.json_array_parser import JsonArrayParser
+from sglang.srt.function_call.utils import get_json_schema_constraint
 from sglang.srt.parser.reasoning_parser import ReasoningParser
 
 from .utils import random_call_id
 
+logger = logging.getLogger(__name__)
+
+# Union of parser types used for tool call detection.
+# - FunctionCallParser: model-specific format detection (tool_choice="auto")
+# - JsonArrayParser: direct JSON array parsing under constrained decoding
+#   (tool_choice="required" or named function)
+ToolCallParserType: TypeAlias = FunctionCallParser | JsonArrayParser
+
 
 @dataclass
 class SglangPreprocessResult:
     """Result of SGLang preprocessing."""
 
     prompt_token_ids: list[int]
-    tool_call_parser: FunctionCallParser | None
+    tool_call_parser: ToolCallParserType | None
     reasoning_parser: ReasoningParser | None
+    guided_decoding: dict[str, Any] | None
     request: dict[str, Any]
 
 
@@ -64,7 +82,7 @@ def create_parsers(
     tool_call_parser_name: str | None,
     reasoning_parser_name: str | None,
     sglang_tools: list[SglangTool] | None = None,
-) -> tuple[FunctionCallParser | None, ReasoningParser | None]:
+) -> tuple[ToolCallParserType | None, ReasoningParser | None]:
     """Create tool call and reasoning parsers for a request.
 
     Shared by both the single-process preprocessing path and the pool path
@@ -72,13 +90,21 @@ def create_parsers(
 
     If ``sglang_tools`` is provided, reuses them; otherwise converts from
     the request's ``tools`` field.
+
+    For ``tool_choice="required"`` or a named function, uses
+    :class:`JsonArrayParser` (matching native SGLang) since guided decoding
+    constrains the output to a JSON array.  Otherwise uses the model-specific
+    :class:`FunctionCallParser`.
     """
     if sglang_tools is None:
         sglang_tools = convert_tools(request.get("tools"))
     tool_choice = request.get("tool_choice", "auto")
 
-    tool_call_parser = None
-    if tool_call_parser_name and sglang_tools and tool_choice != "none":
+    tool_call_parser: ToolCallParserType | None = None
+    if sglang_tools and tool_choice != "none":
+        if tool_choice == "required" or _is_named_tool_choice(tool_choice):
+            tool_call_parser = JsonArrayParser()
+        elif tool_call_parser_name:
             tool_call_parser = FunctionCallParser(
                 tools=sglang_tools,
                 tool_call_parser=tool_call_parser_name,
@@ -94,6 +120,78 @@ def create_parsers(
     return tool_call_parser, reasoning_parser
 
 
+def _is_named_tool_choice(tool_choice: Any) -> bool:
+    return (
+        isinstance(tool_choice, dict)
+        and tool_choice.get("type") == "function"
+        and isinstance(tool_choice.get("function"), dict)
+        and bool(tool_choice["function"].get("name"))
+    )
+
+
+def build_tool_call_guided_decoding(
+    request: dict[str, Any],
+    *,
+    tool_call_parser_name: str | None,
+    sglang_tools: list[SglangTool] | None,
+) -> dict[str, Any] | None:
+    """Build native-SGLang-like tool call constraints for guided decoding."""
+    if not sglang_tools:
+        return None
+
+    tool_choice = request.get("tool_choice", "auto")
+    if tool_choice == "none":
+        return None
+
+    parallel_tool_calls = request.get("parallel_tool_calls")
+    constraint: Any = None
+
+    if tool_choice == "required" or _is_named_tool_choice(tool_choice):
+        # get_json_schema_constraint branches on isinstance(tool_choice,
+        # ToolChoice) for the named-function case — passing our raw dict
+        # would silently fall through and return None, disabling guided
+        # decoding and letting the model omit required fields.
+        sglang_tool_choice: Any = tool_choice
+        if _is_named_tool_choice(tool_choice):
+            sglang_tool_choice = SglangToolChoice(
+                type="function",
+                function=SglangToolChoiceFuncName(
+                    name=tool_choice["function"]["name"],
+                ),
+            )
+        constraint = (
+            "json_schema",
+            get_json_schema_constraint(
+                sglang_tools,
+                sglang_tool_choice,
+                parallel_tool_calls=parallel_tool_calls,
+            ),
+        )
+    elif tool_call_parser_name:
+        parser = FunctionCallParser(
+            tools=sglang_tools,
+            tool_call_parser=tool_call_parser_name,
+        )
+        constraint = parser.get_structure_constraint(
+            tool_choice,
+            parallel_tool_calls=parallel_tool_calls,
+        )
+
+    if isinstance(constraint, tuple) and len(constraint) == 2:
+        if constraint[0] == "json_schema":
+            return {"json": constraint[1]}
+        if constraint[0] == "structural_tag":
+            tag_value = constraint[1]
+            # SGLang returns a Pydantic model (LegacyStructuralTagResponseFormat)
+            # here.  Convert to a plain dict before it hits the RPC layer —
+            # msgpack/serde_json cannot serialize BaseModel instances.
+            if hasattr(tag_value, "model_dump"):
+                tag_value = tag_value.model_dump()
+            return {"structural_tag": tag_value}
+
+    return None
+
+
 def _normalize_prompt_token_ids(prompt_token_ids: Any) -> list[int]:
     if isinstance(prompt_token_ids, list):
         return prompt_token_ids
@@ -127,6 +225,20 @@ def preprocess_chat_request(
     # Convert tools to SGLang format (done once, shared with parser creation)
     sglang_tools = convert_tools(request.get("tools"))
 
+    # Reject a named tool_choice whose function is missing from tools —
+    # otherwise the chat template would render with zero tools while
+    # guided decoding still constrains the output to that function's
+    # schema, producing confusing model behavior.
+    tool_choice = request.get("tool_choice", "auto")
+    if _is_named_tool_choice(tool_choice):
+        chosen_name = tool_choice["function"]["name"]
+        available_names = {t.function.name for t in (sglang_tools or [])}
+        if chosen_name not in available_names:
+            raise ValueError(
+                f"tool_choice names function {chosen_name!r}, but it is not "
+                f"present in tools (available: {sorted(available_names) or 'none'})"
+            )
+
     # Build template kwargs -- single call for rendering + tokenization
     template_kwargs: dict[str, Any] = {
         "add_generation_prompt": True,
@@ -134,10 +246,17 @@ def preprocess_chat_request(
     }
     # Strip tools from template when tool_choice=none so the model doesn't
     # see them and generate raw XML tool calls in its response.
-    tool_choice = request.get("tool_choice", "auto")
+    # When tool_choice names a specific function, only include that tool
+    # in the template so the model doesn't see irrelevant definitions.
     if sglang_tools and not (
         exclude_tools_when_tool_choice_none and tool_choice == "none"
     ):
+        if _is_named_tool_choice(tool_choice):
+            chosen_name = tool_choice["function"]["name"]
+            template_kwargs["tools"] = [
+                t.model_dump() for t in sglang_tools if t.function.name == chosen_name
+            ]
+        else:
             template_kwargs["tools"] = [t.model_dump() for t in sglang_tools]
 
     prompt_token_ids = _normalize_prompt_token_ids(
@@ -150,11 +269,17 @@ def preprocess_chat_request(
         reasoning_parser_name=reasoning_parser_name,
         sglang_tools=sglang_tools,
     )
+    guided_decoding = build_tool_call_guided_decoding(
+        request,
+        tool_call_parser_name=tool_call_parser_name,
+        sglang_tools=sglang_tools,
+    )
 
     return SglangPreprocessResult(
         prompt_token_ids=prompt_token_ids,
         tool_call_parser=tool_call_parser,
         reasoning_parser=reasoning_parser,
+        guided_decoding=guided_decoding,
         request=request,
     )
 
@@ -163,13 +288,102 @@ def _random_call_id() -> str:
     return random_call_id()
 
 
+def _get_history_tool_calls_count(messages: list[dict[str, Any]]) -> int:
+    """Count prior assistant tool calls for parser-specific ID generation."""
+    count = 0
+    for msg in messages:
+        if msg.get("role") != "assistant":
+            continue
+        tool_calls = msg.get("tool_calls")
+        if isinstance(tool_calls, list):
+            count += len(tool_calls)
+    return count
+
+
+def _tool_call_id_for_parser(
+    parser_name: str | None,
+    name: str,
+    index: int,
+    history_tool_calls_count: int,
+) -> str:
+    """Match native SGLang tool-call ID behavior for parser-specific formats.
+
+    ``index`` is the sequential position of this call within the current
+    response — callers must pass the same index they use as the dict key
+    for the call, so the ID stays consistent with the emitted ``index``
+    field.  For ``parse_non_stream`` output, ``ToolCallItem.tool_index``
+    can instead reflect the tool-definition position, so it is not safe
+    to read here directly.
+    """
+    if parser_name != "kimi_k2":
+        return _random_call_id()
+    return f"functions.{name or ''}:{history_tool_calls_count + index}"
+
+
+def _parse_json_array_buffer(buffer: str) -> list[ToolCallItem]:
+    """Parse a JSON array buffer from constrained decoding into ToolCallItems.
+
+    Used as the fallback when JsonArrayParser's streaming parsing missed
+    arguments (same chunking-sensitivity issue as FunctionCallParser).
+    Mirrors SGLang native's ``orjson.loads`` path in ``_process_tool_calls``.
+
+    The buffer may contain trailing special tokens (e.g. ``<|endoftext|>``)
+    from incremental detokenization with ``skip_special_tokens=False``.
+    If the full buffer is not valid JSON, we extract the substring between
+    the first ``[`` and last ``]`` and retry.
+    """
+    data = _try_parse_json_array(buffer)
+    if data is None:
+        return []
+    calls: list[ToolCallItem] = []
+    for i, tool in enumerate(data):
+        if not isinstance(tool, dict):
+            continue
+        name = tool.get("name", "")
+        params = tool.get("parameters")
+        if params is None:
+            params = tool.get("arguments")
+        if params is not None and not isinstance(params, str):
+            params = json.dumps(params, ensure_ascii=False)
+        calls.append(
+            ToolCallItem(
+                tool_index=i,
+                name=name,
+                parameters=params if params is not None else "",
+            )
+        )
+    return calls
+
+
+def _try_parse_json_array(text: str) -> list | None:
+    """Try to parse a JSON array from *text*, tolerating surrounding noise."""
+    try:
+        data = json.loads(text)
+        if isinstance(data, list):
+            return data
+    except (json.JSONDecodeError, TypeError):
+        pass
+    # Retry: extract the outermost [...] substring (handles trailing
+    # special tokens or leading content text).
+    start = text.find("[")
+    end = text.rfind("]")
+    if start != -1 and end > start:
+        try:
+            data = json.loads(text[start : end + 1])
+            if isinstance(data, list):
+                return data
+        except (json.JSONDecodeError, TypeError):
+            pass
+    return None
+
+
 class SglangStreamingPostProcessor:
     """Streaming post-processor using SGLang parsers and HF tokenizer detokenization.
 
     Handles:
     - Incremental detokenization via sliding-window decode (6-token lookback)
     - Reasoning content extraction via SGLang ReasoningParser
-    - Tool call parsing via SGLang FunctionCallParser (parameter deltas)
+    - Tool call parsing via SGLang FunctionCallParser or JsonArrayParser
     """
 
     # Lookback window size for incremental detokenization.  UTF-8 characters
@@ -182,26 +396,46 @@ class SglangStreamingPostProcessor:
         self,
         *,
         tokenizer,
-        tool_call_parser: FunctionCallParser | None,
+        tool_call_parser: ToolCallParserType | None,
         reasoning_parser: ReasoningParser | None,
+        history_tool_calls_count: int = 0,
+        sglang_tools: list[SglangTool] | None = None,
+        tool_call_parser_name: str | None = None,
     ) -> None:
         self.tokenizer = tokenizer
         self.tool_call_parser = tool_call_parser
         self.reasoning_parser = reasoning_parser
+        self.history_tool_calls_count = history_tool_calls_count
+        self._sglang_tools = sglang_tools or []
+        self._tool_call_parser_name = tool_call_parser_name
         self._fast_plain_text = tool_call_parser is None and reasoning_parser is None
+        # Preserve special tokens when a tool call parser is active so
+        # delimiter tokens (e.g. <|tool_call|>) remain visible to the parser.
+        self._skip_special_tokens = tool_call_parser is None
+        self._is_json_array_parser = isinstance(tool_call_parser, JsonArrayParser)
 
         self._all_token_ids: list[int] = []
         # Tool call accumulation.  SGLang's streaming parser returns
         # deltas (name in one chunk, argument fragments across subsequent
-        # chunks).  However, when the complete tool-call JSON arrives in a
-        # single chunk the parser emits the name but never streams
-        # arguments (a chunking-sensitivity issue in the base detector).
-        # We accumulate names + arg fragments from streaming deltas and,
-        # on finish, fall back to parse_non_stream on the detector buffer
-        # for any tool call whose arguments are still missing.
+        # chunks).  However, the base detector processes at most one event
+        # per call (a name OR an argument diff), and the post-processor
+        # calls it only once per token batch.  When multiple tool calls
+        # arrive together, later calls may not be detected during streaming.
+        # We accumulate all text fed to the parser and, on finish, re-parse
+        # the full text to recover any missed tool calls or arguments.
         self._tool_call_ids: dict[int, str] = {}  # tool_index -> call_id
         self._tool_call_names: dict[int, str] = {}  # tool_index -> name
         self._tool_call_args: dict[int, list[str]] = {}  # tool_index -> arg chunks
+        # Full text accumulator for robust finish-time re-parse.
+        self._tool_text_parts: list[str] = []
+
+    def _tool_call_id(self, name: str, index: int) -> str:
+        return _tool_call_id_for_parser(
+            self._tool_call_parser_name,
+            name,
+            index,
+            self.history_tool_calls_count,
+        )
 
     def _incremental_decode(self, new_token_ids: list[int]) -> str:
         """Decode new tokens with lookback window for multi-byte char boundaries.
@@ -226,14 +460,18 @@ class SglangStreamingPostProcessor:
         # Decode lookback-only prefix (before new tokens)
         prefix_tokens = self._all_token_ids[start:prev_count]
         prefix_text = (
-            self.tokenizer.decode(prefix_tokens, skip_special_tokens=True)
+            self.tokenizer.decode(
+                prefix_tokens, skip_special_tokens=self._skip_special_tokens
+            )
             if prefix_tokens
             else ""
         )
 
         # Decode lookback + new tokens together
         window_tokens = self._all_token_ids[start:]
-        window_text = self.tokenizer.decode(window_tokens, skip_special_tokens=True)
+        window_text = self.tokenizer.decode(
+            window_tokens, skip_special_tokens=self._skip_special_tokens
+        )
 
         return window_text[len(prefix_text) :]
 
@@ -282,6 +520,15 @@ class SglangStreamingPostProcessor:
         content_text = normal_text
 
         if self.tool_call_parser and normal_text:
+            # Accumulate raw text for finish-time re-parse.
+            self._tool_text_parts.append(normal_text)
+
+            if self._is_json_array_parser:
+                result = self.tool_call_parser.parse_streaming_increment(
+                    normal_text, self._sglang_tools
+                )
+                parsed_text, tool_calls = result.normal_text, result.calls
+            else:
                 parsed_text, tool_calls = self.tool_call_parser.parse_stream_chunk(
                     normal_text
                 )
@@ -290,7 +537,7 @@ class SglangStreamingPostProcessor:
             for tc in tool_calls:
                 idx = tc.tool_index
                 if idx not in self._tool_call_ids:
-                    self._tool_call_ids[idx] = _random_call_id()
+                    self._tool_call_ids[idx] = self._tool_call_id(tc.name or "", idx)
                 if tc.name:
                     self._tool_call_names[idx] = tc.name
                 if tc.parameters:
@@ -307,26 +554,128 @@ class SglangStreamingPostProcessor:
             delta["reasoning_content"] = reasoning_text
             has_content = True
 
-        # Emit complete tool calls on finish.  For any tool call whose
-        # arguments are still empty (chunking-sensitivity issue), fall
-        # back to parse_non_stream on the detector's buffer.
-        if finish_reason and self._tool_call_names:
+        # On finish, re-parse the full accumulated text to recover tool
+        # calls or arguments that the streaming parser missed.
+        #
+        # The streaming parser (BaseFormatDetector.parse_streaming_increment)
+        # processes at most one event per invocation — a tool name OR an
+        # argument diff — and the post-processor calls it once per token
+        # batch.  When multiple tool calls arrive together or the complete
+        # JSON lands in a single chunk, later calls (or arguments) may
+        # never be detected during streaming.
+        #
+        # The re-parse uses the accumulated text (not the parser's internal
+        # _buffer, which is consumed during streaming) and assigns
+        # sequential indices to match the OpenAI API convention.
+        if (
+            finish_reason
+            and self.tool_call_parser is not None
+            and self._tool_text_parts
+        ):
+            # Purge streaming results that don't match any known tool.
+            # When guided decoding is not enforced the streaming parser
+            # can misidentify words in the prompt (e.g. a person's name)
+            # as function names.
+            known_names = (
+                {t.function.name for t in self._sglang_tools}
+                if self._sglang_tools
+                else set()
+            )
+            if known_names:
+                for idx in list(self._tool_call_names):
+                    if self._tool_call_names[idx] not in known_names:
+                        del self._tool_call_names[idx]
+                        self._tool_call_ids.pop(idx, None)
+                        self._tool_call_args.pop(idx, None)
+
+            # Discard malformed (non-JSON) argument fragments that the
+            # streaming parser accumulated from mixed content.
+            for idx in list(self._tool_call_args):
+                combined = "".join(self._tool_call_args[idx])
+                if combined:
+                    try:
+                        json.loads(combined)
+                    except (json.JSONDecodeError, ValueError):
+                        del self._tool_call_args[idx]
+
+            missing_names = not self._tool_call_names
             missing_args = any(
                 idx not in self._tool_call_args for idx in self._tool_call_names
             )
-            if missing_args and self.tool_call_parser is not None:
-                buffer = getattr(self.tool_call_parser.detector, "_buffer", "")
-                if buffer:
-                    _, final_calls = self.tool_call_parser.parse_non_stream(buffer)
-                    for tc in final_calls:
-                        idx = tc.tool_index
-                        if idx not in self._tool_call_ids:
-                            self._tool_call_ids[idx] = _random_call_id()
+            should_reparse = False
+            full_text = ""
+            if missing_names or missing_args:
+                full_text = "".join(self._tool_text_parts)
+                # Skip the re-parse when the accumulated text has no
+                # tool-call markers.  Avoids wasted `parse_non_stream`
+                # work on plain-text responses (common when tools are
+                # offered but the model replies without calling any) and
+                # guards against detectors that raise on arbitrary input.
+                should_reparse = bool(
+                    full_text
+                ) and self.tool_call_parser.has_tool_call(full_text)
+
+            if should_reparse:
+                if self._is_json_array_parser:
+                    final_calls = _parse_json_array_buffer(full_text)
+                    # Secondary fallback: when guided decoding did not
+                    # constrain the output (e.g. the backend doesn't
+                    # support it), the model may have produced tool calls
+                    # in its native format.  Try the model-specific
+                    # parser so we don't silently drop them.
+                    if (
+                        not final_calls
+                        and self._tool_call_parser_name
+                        and self._sglang_tools
+                    ):
+                        try:
+                            fcp = FunctionCallParser(
+                                tools=self._sglang_tools,
+                                tool_call_parser=self._tool_call_parser_name,
+                            )
+                            _, final_calls = fcp.parse_non_stream(full_text)
+                        except (
+                            ValueError,
+                            KeyError,
+                            json.JSONDecodeError,
+                            IndexError,
+                        ) as e:
+                            # Fallback path: model-native tool-call text is
+                            # malformed. Log and return no tool calls rather
+                            # than crashing the whole response — the primary
+                            # JSON-array path has already failed, and the
+                            # normal text is still usable.
+                            logger.warning(
+                                "Native tool-call fallback parse failed (parser=%r): %s",
+                                self._tool_call_parser_name,
+                                e,
+                            )
+                            final_calls = []
+                else:
+                    _, final_calls = self.tool_call_parser.parse_non_stream(full_text)
+                # Filter to known tool names (reuse set from above).
+                if known_names:
+                    final_calls = [tc for tc in final_calls if tc.name in known_names]
+                # Re-index sequentially so repeated calls to the same
+                # tool get distinct indices (parse_non_stream may assign
+                # indices based on the tool-definition position instead).
+                # When the re-parse returns results, it is authoritative:
+                # clear streaming state first so we don't mix a name from
+                # the re-parse with args from streaming at the same index.
+                if final_calls:
+                    self._tool_call_ids.clear()
+                    self._tool_call_names.clear()
+                    self._tool_call_args.clear()
+                    for seq_idx, tc in enumerate(final_calls):
+                        self._tool_call_ids[seq_idx] = self._tool_call_id(
+                            tc.name or "", seq_idx
+                        )
                         if tc.name:
-                            self._tool_call_names[idx] = tc.name
+                            self._tool_call_names[seq_idx] = tc.name
                         if tc.parameters:
-                            self._tool_call_args[idx] = [tc.parameters]
+                            self._tool_call_args[seq_idx] = [tc.parameters]
 
+        if finish_reason and self._tool_call_names:
             tool_calls_out: list[dict[str, Any]] = []
             for idx in sorted(self._tool_call_names):
                 tool_calls_out.append(
@@ -343,11 +692,17 @@ class SglangStreamingPostProcessor:
             delta["tool_calls"] = tool_calls_out
             has_content = True
 
-        if has_content or finish_reason:
+        # Rewrite finish_reason "stop" → "tool_calls" when tool calls were
+        # detected, matching the OpenAI API spec and official SGLang behaviour.
+        effective_finish = finish_reason
+        if finish_reason == "stop" and self._tool_call_names:
+            effective_finish = "tool_calls"
+
+        if has_content or effective_finish:
             return {
                 "index": 0,
                 "delta": delta if has_content else {},
-                "finish_reason": finish_reason,
+                "finish_reason": effective_finish,
                 "logprobs": None,
             }
 

components/src/dynamo/frontend/sglang_processor.py

@@ -32,6 +32,9 @@ from dynamo.runtime import DistributedRuntime
 
 from .sglang_prepost import (
     SglangStreamingPostProcessor,
+    ToolCallParserType,
+    _get_history_tool_calls_count,
+    convert_tools,
     create_parsers,
     preprocess_chat_request,
 )
@@ -117,11 +120,12 @@ def _init_worker(
     tool_call_parser_name: str | None,
     reasoning_parser_name: str | None,
     exclude_tools_when_tool_choice_none: bool = True,
+    trust_remote_code: bool = False,
 ) -> None:
     """Initialize a worker process with its own tokenizer."""
     global _w_tokenizer, _w_tool_call_parser_name, _w_reasoning_parser_name
     global _w_exclude_tools_when_tool_choice_none
-    _w_tokenizer = get_tokenizer(model_path)
+    _w_tokenizer = get_tokenizer(model_path, trust_remote_code=trust_remote_code)
     _w_tool_call_parser_name = tool_call_parser_name
     _w_reasoning_parser_name = reasoning_parser_name
     _w_exclude_tools_when_tool_choice_none = exclude_tools_when_tool_choice_none
@@ -146,7 +150,12 @@ def _preprocess_worker(
         raise PreprocessError(_unsupported_n_error(n))
 
     dynamo_preproc = _build_dynamo_preproc(
-        request, pre.prompt_token_ids, model_name, eos_token_id
+        request,
+        pre.prompt_token_ids,
+        model_name,
+        eos_token_id,
+        pre.guided_decoding,
+        pre.tool_call_parser,
     )
 
     return SglangPreprocessWorkerResult(
@@ -161,6 +170,8 @@ def _build_dynamo_preproc(
     prompt_token_ids: list[int],
     model_name: str,
     eos_token_id: int | None,
+    guided_decoding: dict[str, Any] | None = None,
+    tool_call_parser: ToolCallParserType | None = None,
 ) -> dict[str, Any]:
     """Build the Dynamo preprocessed request dict from request fields."""
     max_tokens = request.get("max_completion_tokens") or request.get("max_tokens")
@@ -205,11 +216,16 @@ def _build_dynamo_preproc(
             "top_k": request.get("top_k", 0) or -1,
             "min_p": request.get("min_p", 0.0),
             "seed": request.get("seed"),
+            "guided_decoding": guided_decoding,
         },
         "output_options": {
             "logprobs": logprobs_val,
             "prompt_logprobs": None,
-            "skip_special_tokens": True,
+            # Preserve special tokens only when a tool-call parser is
+            # actually active — the parser needs delimiter tokens
+            # (e.g. <|tool_call|>) to detect calls. Mirrors the
+            # post-processor's _skip_special_tokens logic.
+            "skip_special_tokens": tool_call_parser is None,
         },
         "eos_token_ids": [eos_token_id] if eos_token_id is not None else [],
         "annotations": [],
@@ -320,7 +336,12 @@ class SglangProcessor:
                 return
 
             dynamo_preproc = _build_dynamo_preproc(
-                request, tokens, request["model"], self.eos_token_id
+                request,
+                tokens,
+                request["model"],
+                self.eos_token_id,
+                pre.guided_decoding,
+                pre.tool_call_parser,
             )
         except Exception as exc:
             logger.exception("SGLang preprocessing failed for request %s", request_id)
@@ -336,6 +357,11 @@ class SglangProcessor:
             tokenizer=self.tokenizer,
             tool_call_parser=pre.tool_call_parser,
             reasoning_parser=pre.reasoning_parser,
+            history_tool_calls_count=_get_history_tool_calls_count(
+                request.get("messages", [])
+            ),
+            sglang_tools=convert_tools(request.get("tools")),
+            tool_call_parser_name=self.tool_call_parser_name,
         )
 
         async for item in self._generate_and_stream(
@@ -389,6 +415,11 @@ class SglangProcessor:
             tokenizer=self.tokenizer,
             tool_call_parser=tool_call_parser,
             reasoning_parser=reasoning_parser,
+            history_tool_calls_count=_get_history_tool_calls_count(
+                request.get("messages", [])
+            ),
+            sglang_tools=convert_tools(request.get("tools")),
+            tool_call_parser_name=self.tool_call_parser_name,
         )
 
         async for item in self._generate_and_stream(
@@ -530,6 +561,7 @@ class SglangEngineFactory:
         self.tool_call_parser_name = tool_call_parser_name
         self.reasoning_parser_name = reasoning_parser_name
 
+        self.trust_remote_code = config.trust_remote_code
         self.stream_interval = 20
         raw_stream_interval = os.getenv("DYN_SGLANG_STREAM_INTERVAL")
         if raw_stream_interval:
@@ -560,7 +592,7 @@ class SglangEngineFactory:
             await fetch_model(source_path, ignore_weights=True)
 
         logger.info("Loading SGLang tokenizer from %s", source_path)
-        tokenizer = get_tokenizer(source_path)
+        tokenizer = get_tokenizer(source_path, trust_remote_code=self.trust_remote_code)
 
         eos_token_id = getattr(tokenizer, "eos_token_id", None)
 
@@ -610,6 +642,7 @@ class SglangEngineFactory:
                     tool_call_parser_name,
                     reasoning_parser_name,
                     self.config.exclude_tools_when_tool_choice_none,
+                    self.trust_remote_code,
                 ),
             )
             futures = [

components/src/dynamo/frontend/tests/test_sglang_processor_unit.py

@@ -10,7 +10,11 @@ Parallels test_vllm_unit.py for the vLLM backend.
 """
 
 
+import json
+
 import pytest
+from sglang.srt.function_call.function_call_parser import FunctionCallParser
+from sglang.srt.function_call.json_array_parser import JsonArrayParser
 from sglang.srt.utils.hf_transformers_utils import get_tokenizer
 
 import dynamo.frontend.sglang_processor as sglang_processor_module
@@ -18,6 +22,8 @@ from dynamo.frontend.sglang_prepost import (
     SglangPreprocessResult,
     SglangStreamingPostProcessor,
     _normalize_prompt_token_ids,
+    _parse_json_array_buffer,
+    build_tool_call_guided_decoding,
     convert_tools,
     create_parsers,
     preprocess_chat_request,
@@ -119,6 +125,18 @@ class TestBuildDynamoPreproc:
         assert sampling["repetition_penalty"] == 1.1
         assert sampling["seed"] == 42
 
+    def test_guided_decoding_passthrough(self):
+        result = _build_dynamo_preproc(
+            {"model": "test"},
+            prompt_token_ids=[1, 2, 3],
+            model_name="test",
+            eos_token_id=None,
+            guided_decoding={"json": {"type": "object"}},
+        )
+        assert result["sampling_options"]["guided_decoding"] == {
+            "json": {"type": "object"}
+        }
+
     def test_stop_conditions_string(self):
         """Single stop string is wrapped in a list."""
         result = _build_dynamo_preproc(
@@ -368,6 +386,92 @@ class TestCreateParsers:
         assert tcp is None
         assert rp is not None
 
+
+class TestBuildToolCallGuidedDecoding:
+    def test_none_when_no_tools(self):
+        assert (
+            build_tool_call_guided_decoding(
+                {"tool_choice": "auto"},
+                tool_call_parser_name="hermes",
+                sglang_tools=None,
+            )
+            is None
+        )
+
+    def test_none_when_tool_choice_none(self):
+        tools = convert_tools(
+            [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "parameters": {"type": "object", "properties": {}},
+                    },
+                }
+            ]
+        )
+        assert (
+            build_tool_call_guided_decoding(
+                {"tool_choice": "none"},
+                tool_call_parser_name="hermes",
+                sglang_tools=tools,
+            )
+            is None
+        )
+
+    def test_required_tool_choice_builds_json_schema_guidance(self):
+        tools = convert_tools(
+            [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "parameters": {
+                            "type": "object",
+                            "properties": {"city": {"type": "string"}},
+                            "required": ["city"],
+                        },
+                    },
+                }
+            ]
+        )
+
+        guided = build_tool_call_guided_decoding(
+            {"tool_choice": "required"},
+            tool_call_parser_name="hermes",
+            sglang_tools=tools,
+        )
+
+        assert isinstance(guided, dict)
+        assert "json" in guided
+
+    def test_auto_strict_tools_can_build_structural_tag_guidance(self):
+        tools = convert_tools(
+            [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "strict": True,
+                        "parameters": {
+                            "type": "object",
+                            "properties": {"city": {"type": "string"}},
+                            "required": ["city"],
+                        },
+                    },
+                }
+            ]
+        )
+
+        guided = build_tool_call_guided_decoding(
+            {"tool_choice": "auto"},
+            tool_call_parser_name="kimi_k2",
+            sglang_tools=tools,
+        )
+
+        assert isinstance(guided, dict)
+        assert "structural_tag" in guided
+
     def test_tool_parser_requires_tools(self):
         """Tool parser is not created if no tools in request."""
         tcp, rp = create_parsers(
@@ -437,6 +541,170 @@ class TestCreateParsers:
         assert tcp is not None
         assert rp is not None
 
+    def test_required_creates_json_array_parser(self):
+        """tool_choice='required' creates JsonArrayParser, not FunctionCallParser."""
+        request = {
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "f",
+                        "description": "d",
+                        "parameters": {},
+                    },
+                }
+            ],
+            "tool_choice": "required",
+        }
+        tcp, _ = create_parsers(
+            request, tool_call_parser_name="hermes", reasoning_parser_name=None
+        )
+        assert isinstance(tcp, JsonArrayParser)
+
+    def test_named_tool_choice_creates_json_array_parser(self):
+        """Named tool_choice creates JsonArrayParser."""
+        request = {
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "description": "Get weather",
+                        "parameters": {},
+                    },
+                }
+            ],
+            "tool_choice": {
+                "type": "function",
+                "function": {"name": "get_weather"},
+            },
+        }
+        tcp, _ = create_parsers(
+            request, tool_call_parser_name="hermes", reasoning_parser_name=None
+        )
+        assert isinstance(tcp, JsonArrayParser)
+
+    def test_auto_creates_function_call_parser(self):
+        """tool_choice='auto' creates FunctionCallParser."""
+        request = {
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "f",
+                        "description": "d",
+                        "parameters": {},
+                    },
+                }
+            ],
+            "tool_choice": "auto",
+        }
+        tcp, _ = create_parsers(
+            request, tool_call_parser_name="hermes", reasoning_parser_name=None
+        )
+        assert isinstance(tcp, FunctionCallParser)
+
+    def test_required_without_parser_name_still_creates_json_array_parser(self):
+        """tool_choice='required' doesn't need tool_call_parser_name."""
+        request = {
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "f",
+                        "description": "d",
+                        "parameters": {},
+                    },
+                }
+            ],
+            "tool_choice": "required",
+        }
+        tcp, _ = create_parsers(
+            request, tool_call_parser_name=None, reasoning_parser_name=None
+        )
+        assert isinstance(tcp, JsonArrayParser)
+
+
+# ---------------------------------------------------------------------------
+# _parse_json_array_buffer
+# ---------------------------------------------------------------------------
+
+
+class TestParseJsonArrayBuffer:
+    """Test JSON array fallback parser for constrained decoding output."""
+
+    def test_single_tool_call(self):
+        buffer = json.dumps([{"name": "get_weather", "parameters": {"city": "NYC"}}])
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert calls[0].name == "get_weather"
+        assert calls[0].tool_index == 0
+        assert json.loads(calls[0].parameters) == {"city": "NYC"}
+
+    def test_multiple_tool_calls(self):
+        buffer = json.dumps(
+            [
+                {"name": "get_weather", "parameters": {"city": "NYC"}},
+                {"name": "search", "parameters": {"q": "hello"}},
+            ]
+        )
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 2
+        assert calls[0].name == "get_weather"
+        assert calls[0].tool_index == 0
+        assert calls[1].name == "search"
+        assert calls[1].tool_index == 1
+
+    def test_arguments_key_also_accepted(self):
+        """Some formats use 'arguments' instead of 'parameters'."""
+        buffer = json.dumps([{"name": "f", "arguments": {"x": 1}}])
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert json.loads(calls[0].parameters) == {"x": 1}
+
+    def test_string_parameters_preserved(self):
+        buffer = json.dumps([{"name": "f", "parameters": "already_a_string"}])
+        calls = _parse_json_array_buffer(buffer)
+        assert calls[0].parameters == "already_a_string"
+
+    def test_invalid_json_returns_empty(self):
+        assert _parse_json_array_buffer("not json") == []
+
+    def test_non_array_returns_empty(self):
+        assert _parse_json_array_buffer('{"name": "f"}') == []
+
+    def test_empty_buffer_returns_empty(self):
+        assert _parse_json_array_buffer("") == []
+
+    def test_non_dict_items_skipped(self):
+        buffer = json.dumps(["not_a_dict", {"name": "f", "parameters": {}}])
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert calls[0].name == "f"
+        assert calls[0].tool_index == 1
+
+    def test_trailing_special_token(self):
+        """Trailing EOS/special tokens should not break parsing."""
+        buffer = '[{"name": "f", "parameters": {"x": 1}}]<|endoftext|>'
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert calls[0].name == "f"
+        assert json.loads(calls[0].parameters) == {"x": 1}
+
+    def test_leading_text_with_array(self):
+        """Leading non-JSON text before the array should be tolerated."""
+        buffer = 'some preamble [{"name": "f", "parameters": {"x": 1}}]'
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert calls[0].name == "f"
+
+    def test_trailing_and_leading_noise(self):
+        """Both leading and trailing noise."""
+        buffer = 'text [{"name": "g", "parameters": {"y": 2}}] <|end|>'
+        calls = _parse_json_array_buffer(buffer)
+        assert len(calls) == 1
+        assert calls[0].name == "g"
+
 
 class TestNormalizePromptTokenIds:
     def test_batch_encoding_like_object_uses_input_ids(self):
@@ -641,6 +909,37 @@ class TestPreprocessChatRequest:
             with_auto.prompt_token_ids
         ), "tool_choice=none with flag off should keep tools in template"
 
+    def test_named_tool_choice_missing_function_raises(self, tokenizer):
+        """Named tool_choice referencing a function absent from tools raises ValueError."""
+        request = {
+            "model": MODEL,
+            "messages": [{"role": "user", "content": "Hello"}],
+            "tools": [
+                {
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "description": "Get weather",
+                        "parameters": {
+                            "type": "object",
+                            "properties": {"city": {"type": "string"}},
+                        },
+                    },
+                }
+            ],
+            "tool_choice": {
+                "type": "function",
+                "function": {"name": "does_not_exist"},
+            },
+        }
+        with pytest.raises(ValueError, match="does_not_exist"):
+            preprocess_chat_request(
+                request,
+                tokenizer=tokenizer,
+                tool_call_parser_name="hermes",
+                reasoning_parser_name=None,
+            )
+
     def test_init_worker_propagates_exclude_flag_true(self):
         """_init_worker sets the worker-global exclude_tools flag to True."""
         _init_worker(MODEL, None, None, exclude_tools_when_tool_choice_none=True)

components/src/dynamo/frontend/tests/test_sglang_tool_calls.py

@@ -15,6 +15,7 @@ import pytest
 from sglang.srt.entrypoints.openai.protocol import Function as SglangFunction
 from sglang.srt.entrypoints.openai.protocol import Tool as SglangTool
 from sglang.srt.function_call.function_call_parser import FunctionCallParser
+from sglang.srt.function_call.json_array_parser import JsonArrayParser
 from sglang.srt.parser.reasoning_parser import ReasoningParser
 from sglang.srt.utils.hf_transformers_utils import get_tokenizer
 
@@ -153,6 +154,114 @@ class TestSingleToolCall:
         assert tc[0]["index"] == 0
 
 
+class TestKimiToolCallIds:
+    def test_kimi_uses_history_adjusted_ids(self):
+        class DummyTokenizer:
+            def decode(self, token_ids, skip_special_tokens=True):
+                return "".join(chr(x) for x in token_ids)
+
+        class DummyToolCall:
+            def __init__(self, tool_index, name, parameters):
+                self.tool_index = tool_index
+                self.name = name
+                self.parameters = parameters
+
+        class DummyParser:
+            tool_call_parser = "kimi_k2"
+            detector = type("Detector", (), {"_buffer": ""})()
+
+            def parse_stream_chunk(self, text):
+                return "", [
+                    DummyToolCall(0, "get_weather", '{"city":"Paris"}'),
+                    DummyToolCall(
+                        1, "search_gutenberg_books", '{"search_terms":["Joyce"]}'
+                    ),
+                ]
+
+        post = SglangStreamingPostProcessor(
+            tokenizer=DummyTokenizer(),
+            tool_call_parser=DummyParser(),
+            reasoning_parser=None,
+            history_tool_calls_count=3,
+            tool_call_parser_name="kimi_k2",
+        )
+
+        choice = post.process_output(
+            {
+                "token_ids": [ord("x")],
+                "finish_reason": "stop",
+            }
+        )
+
+        tc = choice["delta"]["tool_calls"]
+        assert [item["id"] for item in tc] == [
+            "functions.get_weather:3",
+            "functions.search_gutenberg_books:4",
+        ]
+
+    def test_kimi_reparse_uses_sequential_index_not_tool_index(self):
+        """kimi_k2 IDs after re-parse use the output position, not tool_index.
+
+        ``FunctionCallParser.parse_non_stream`` can return
+        ``ToolCallItem.tool_index`` values that reflect the tool-definition
+        position rather than the call's sequential position.  IDs must
+        align with the emitted ``index`` field, so they are built from
+        the post-processor's ``seq_idx``.
+        """
+
+        class DummyTokenizer:
+            def decode(self, token_ids, skip_special_tokens=True):
+                return "".join(chr(x) for x in token_ids)
+
+        class DummyToolCall:
+            def __init__(self, tool_index, name, parameters):
+                self.tool_index = tool_index
+                self.name = name
+                self.parameters = parameters
+
+        class DummyParser:
+            tool_call_parser = "kimi_k2"
+            detector = type("Detector", (), {"_buffer": ""})()
+
+            def parse_stream_chunk(self, text):
+                # Streaming misses both calls — forces the re-parse path.
+                return "", []
+
+            def has_tool_call(self, text):
+                return True
+
+            def parse_non_stream(self, text):
+                # Non-sequential tool_index values, as parse_non_stream
+                # sometimes returns tool-definition positions.
+                return "", [
+                    DummyToolCall(5, "get_weather", '{"city":"Paris"}'),
+                    DummyToolCall(2, "search_gutenberg_books", '{"q":"Joyce"}'),
+                ]
+
+        post = SglangStreamingPostProcessor(
+            tokenizer=DummyTokenizer(),
+            tool_call_parser=DummyParser(),
+            reasoning_parser=None,
+            history_tool_calls_count=3,
+            tool_call_parser_name="kimi_k2",
+        )
+
+        choice = post.process_output(
+            {
+                "token_ids": [ord("x")],
+                "finish_reason": "stop",
+            }
+        )
+
+        tc = choice["delta"]["tool_calls"]
+        # IDs must use seq_idx (0, 1) + history (3), not tool_index (5, 2).
+        assert [item["id"] for item in tc] == [
+            "functions.get_weather:3",
+            "functions.search_gutenberg_books:4",
+        ]
+        assert [item["index"] for item in tc] == [0, 1]
+
+
 # ---------------------------------------------------------------------------
 # No reasoning parser
 # ---------------------------------------------------------------------------
@@ -276,3 +385,159 @@ class TestNoToolCalls:
             c = r.get("delta", {}).get("content", "")
             content += c
         assert "Hello, world!" in content
+
+
+# ---------------------------------------------------------------------------
+# Single-chunk tool calls (finish-time re-parse fallback)
+# ---------------------------------------------------------------------------
+
+
+class TestSingleChunkFallback:
+    """When all tool call tokens + finish arrive in one batch, the streaming
+    parser only processes one event.  The finish-time re-parse must recover
+    arguments and any additional tool calls."""
+
+    TEXT = (
+        "<think>\nLet me search for books.\n</think>\n\n"
+        '<tool_call>\n{"name": "search_gutenberg_books", '
+        '"arguments": {"search_terms": ["James Joyce"]}}\n</tool_call>'
+    )
+
+    def test_all_tokens_plus_finish_in_one_batch(self, tokenizer):
+        """Entire response + finish in a single process_output call."""
+        tcp = FunctionCallParser(tools=TOOLS, tool_call_parser="hermes")
+        rp = ReasoningParser(model_type="qwen3", stream_reasoning=True)
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=tcp,
+            reasoning_parser=rp,
+        )
+        token_ids = tokenizer.encode(self.TEXT)
+        # Feed ALL tokens at once with finish_reason
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        assert choice is not None
+        tc = choice.get("delta", {}).get("tool_calls", [])
+        assert len(tc) == 1, f"Expected 1 tool call, got {len(tc)}"
+        assert tc[0]["function"]["name"] == "search_gutenberg_books"
+        args = json.loads(tc[0]["function"]["arguments"])
+        assert args == {"search_terms": ["James Joyce"]}
+
+    def test_multiple_tools_single_chunk(self, tokenizer):
+        """Multiple tool calls in one chunk -- re-parse must find all."""
+        text = (
+            "<think>\nI'll search and check weather.\n</think>\n\n"
+            '<tool_call>\n{"name": "search_gutenberg_books", '
+            '"arguments": {"search_terms": ["Joyce"]}}\n</tool_call>\n'
+            '<tool_call>\n{"name": "get_weather", '
+            '"arguments": {"city": "London"}}\n</tool_call>'
+        )
+        tcp = FunctionCallParser(tools=TOOLS, tool_call_parser="hermes")
+        rp = ReasoningParser(model_type="qwen3", stream_reasoning=True)
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=tcp,
+            reasoning_parser=rp,
+        )
+        token_ids = tokenizer.encode(text)
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        assert choice is not None
+        tc = choice.get("delta", {}).get("tool_calls", [])
+        assert len(tc) == 2, f"Expected 2 tool calls, got {len(tc)}"
+        names = {t["function"]["name"] for t in tc}
+        assert names == {"search_gutenberg_books", "get_weather"}
+        for t in tc:
+            args = json.loads(t["function"]["arguments"])
+            assert args, f"Arguments should not be empty for {t['function']['name']}"
+
+    def test_finish_reason_rewritten_to_tool_calls(self, tokenizer):
+        """finish_reason should be 'tool_calls' when re-parse finds calls."""
+        tcp = FunctionCallParser(tools=TOOLS, tool_call_parser="hermes")
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=tcp,
+            reasoning_parser=None,
+        )
+        text = (
+            '<tool_call>\n{"name": "get_weather", '
+            '"arguments": {"city": "NYC"}}\n</tool_call>'
+        )
+        token_ids = tokenizer.encode(text)
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        assert choice is not None
+        assert choice["finish_reason"] == "tool_calls"
+
+
+# ---------------------------------------------------------------------------
+# JsonArrayParser path (tool_choice="required" / named function)
+# ---------------------------------------------------------------------------
+
+
+class TestJsonArrayParserReparse:
+    """Exercise the JsonArrayParser branch of the finish-time re-parse.
+
+    Under ``tool_choice="required"`` or a named function, guided decoding
+    constrains the model to emit a raw JSON array and
+    SglangStreamingPostProcessor is constructed with a JsonArrayParser
+    instead of a FunctionCallParser. The re-parse path uses
+    ``has_tool_call`` on the parser as a cheap gate and
+    ``_parse_json_array_buffer`` for recovery — this class locks in that
+    API surface so a SGLang upgrade can't silently break it.
+    """
+
+    def test_single_call_reparse(self, tokenizer):
+        """Full JSON array arriving in one chunk triggers the re-parse."""
+        text = '[{"name": "get_weather", "parameters": {"city": "NYC"}}]'
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=JsonArrayParser(),
+            reasoning_parser=None,
+            sglang_tools=TOOLS,
+        )
+        token_ids = tokenizer.encode(text)
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        assert choice is not None
+        tc = choice.get("delta", {}).get("tool_calls", [])
+        assert len(tc) == 1
+        assert tc[0]["function"]["name"] == "get_weather"
+        assert json.loads(tc[0]["function"]["arguments"]) == {"city": "NYC"}
+        assert choice["finish_reason"] == "tool_calls"
+
+    def test_multiple_calls_reparse(self, tokenizer):
+        """Multiple calls in one chunk; re-parse must recover all."""
+        text = (
+            '[{"name": "search_gutenberg_books", '
+            '"parameters": {"search_terms": ["Joyce"]}}, '
+            '{"name": "get_weather", "parameters": {"city": "London"}}]'
+        )
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=JsonArrayParser(),
+            reasoning_parser=None,
+            sglang_tools=TOOLS,
+        )
+        token_ids = tokenizer.encode(text)
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        assert choice is not None
+        tc = choice.get("delta", {}).get("tool_calls", [])
+        assert len(tc) == 2
+        names = {t["function"]["name"] for t in tc}
+        assert names == {"search_gutenberg_books", "get_weather"}
+
+    def test_plain_text_skips_reparse(self, tokenizer):
+        """Plain text with no JSON markers must not crash the re-parse path.
+
+        Locks in that the ``has_tool_call`` gate on JsonArrayParser returns
+        False for text without '[' or '{', so ``_parse_json_array_buffer``
+        and the secondary FunctionCallParser fallback are never reached.
+        """
+        post = SglangStreamingPostProcessor(
+            tokenizer=tokenizer,
+            tool_call_parser=JsonArrayParser(),
+            reasoning_parser=None,
+            sglang_tools=TOOLS,
+        )
+        token_ids = tokenizer.encode("Hello, world!")
+        choice = post.process_output({"token_ids": token_ids, "finish_reason": "stop"})
+        # No tool calls, plain content preserved, no crash.
+        tc = (choice or {}).get("delta", {}).get("tool_calls", [])
+        assert tc == []

components/src/dynamo/frontend/vllm_processor.py

@@ -448,7 +448,7 @@ class EngineFactory:
         tokenizer_mode = getattr(self.flags, "tokenizer_mode", None) or "auto"
         config_format = getattr(self.flags, "config_format", None) or "auto"
         load_format = getattr(self.flags, "load_format", None) or "dummy"
-        trust_remote_code = getattr(self.flags, "trust_remote_code", False)
+        trust_remote_code = self.config.trust_remote_code
         enable_auto_tool_choice = getattr(self.flags, "enable_auto_tool_choice", False)
 
         model_config = ModelConfig(

components/src/dynamo/sglang/request_handlers/handler_base.py

@@ -1062,6 +1062,11 @@ class BaseWorkerHandler(LoraMixin, RLMixin, BaseGenerativeHandler[RequestT, Resp
             json_schema = guided_decoding.get("json")
             if json_schema is not None:
                 return {"json_schema": json.dumps(json_schema)}
+            structural_tag = guided_decoding.get("structural_tag")
+            if structural_tag is not None:
+                if hasattr(structural_tag, "model_dump"):
+                    structural_tag = structural_tag.model_dump()
+                return {"structural_tag": json.dumps(structural_tag)}
         return {}
 
     @staticmethod

tests/frontend/test_tool_calling_sglang.py

+# SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""End-to-end tool calling tests against the Dynamo frontend.
+
+Validates:
+  - Streaming protocol shape (chat.completion.chunk SSE)
+  - Tool-call reconstruction from streamed deltas
+  - Tool-call argument JSON validated against the declared JSON Schema
+  - tool_choice variants: auto / required / none / named function
+  - Multi-turn conversations carrying tool results
+  - Multi-tool parallel calls
+
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import os
+import shutil
+import time
+from dataclasses import dataclass
+from typing import Any, Generator
+
+import pytest
+
+from tests.conftest import EtcdServer, NatsServer
+from tests.utils.managed_process import ManagedProcess
+from tests.utils.payloads import check_models_api
+from tests.utils.port_utils import allocate_ports
+
+openai = pytest.importorskip("openai")
+OpenAI = openai.OpenAI
+jsonschema = pytest.importorskip("jsonschema")
+Draft7Validator = jsonschema.Draft7Validator
+
+logger = logging.getLogger(__name__)
+
+MODEL_NAME = "Qwen/Qwen3-0.6B"
+
+pytestmark = [
+    pytest.mark.sglang,
+    pytest.mark.e2e,
+    pytest.mark.gpu_1,
+    pytest.mark.integration,
+    pytest.mark.pre_merge,
+    pytest.mark.model(MODEL_NAME),
+    pytest.mark.timeout(300),
+]
+
+
+# ---------------------------------------------------------------------------
+# Process management
+# ---------------------------------------------------------------------------
+
+
+def _check_ready(response) -> bool:
+    try:
+        return (response.json() or {}).get("status") == "ready"
+    except ValueError:
+        return False
+
+
+def _prepare_log_dir(request, suffix: str) -> str:
+    log_dir = f"{request.node.name}_{suffix}"
+    shutil.rmtree(log_dir, ignore_errors=True)
+    return log_dir
+
+
+class WorkerProcess(ManagedProcess):
+    """backend worker for the tool-calling tests."""
+
+    def __init__(self, request, *, system_port: int):
+        env = os.environ.copy()
+        env["DYN_LOG"] = "info"
+        env["DYN_SYSTEM_PORT"] = str(system_port)
+        env["DYN_SYSTEM_USE_ENDPOINT_HEALTH_STATUS"] = '["generate"]'
+
+        super().__init__(
+            command=[
+                "python3",
+                "-m",
+                "dynamo.sglang",
+                "--model-path",
+                MODEL_NAME,
+                "--served-model-name",
+                MODEL_NAME,
+                "--trust-remote-code",
+            ],
+            env=env,
+            health_check_urls=[
+                (f"http://localhost:{system_port}/health", _check_ready),
+            ],
+            timeout=600,
+            display_output=True,
+            terminate_all_matching_process_names=False,
+            stragglers=["SGLANG:EngineCore"],
+            straggler_commands=["-m dynamo.sglang"],
+            log_dir=_prepare_log_dir(request, "sglang-worker"),
+        )
+
+
+class ToolCallingFrontendProcess(ManagedProcess):
+    """Frontend HTTP ingress.
+
+    SGLang-specific chat processor, tool-call parser, and reasoning parser
+    flags are only attached when ``sglang`` is importable in the current
+    environment (otherwise the frontend would fail to load them).
+    """
+
+    def __init__(self, request, *, frontend_port: int):
+        env = os.environ.copy()
+        env["DYN_LOG"] = "info"
+        env.pop("DYN_SYSTEM_PORT", None)
+
+        command = [
+            "python3",
+            "-m",
+            "dynamo.frontend",
+            "--http-port",
+            str(frontend_port),
+            "--router-mode",
+            "round-robin",
+            "--dyn-chat-processor",
+            "sglang",
+            "--tool-call-parser",
+            "qwen25",
+            "--reasoning-parser",
+            "qwen3",
+            "--trust-remote-code",
+        ]
+
+        super().__init__(
+            command=command,
+            env=env,
+            health_check_urls=[
+                (f"http://localhost:{frontend_port}/v1/models", check_models_api),
+            ],
+            timeout=240,
+            display_output=True,
+            terminate_all_matching_process_names=False,
+            straggler_commands=["-m dynamo.frontend"],
+            log_dir=_prepare_log_dir(request, "frontend"),
+        )
+
+
+@pytest.fixture(scope="module")
+def runtime_services(request) -> Generator[None, None, None]:
+    """Module-scoped NATS + Etcd for the tool calling stack.
+
+    Inlined (rather than depending on the function-scoped
+    ``runtime_services_dynamic_ports``) so the worker + frontend processes
+    can be reused across all tests in this module.
+    """
+    with NatsServer(request, port=0) as nats, EtcdServer(request, port=0) as etcd:
+        orig_nats = os.environ.get("NATS_SERVER")
+        orig_etcd = os.environ.get("ETCD_ENDPOINTS")
+        os.environ["NATS_SERVER"] = f"nats://localhost:{nats.port}"
+        os.environ["ETCD_ENDPOINTS"] = f"http://localhost:{etcd.port}"
+        try:
+            yield
+        finally:
+            if orig_nats is not None:
+                os.environ["NATS_SERVER"] = orig_nats
+            else:
+                os.environ.pop("NATS_SERVER", None)
+            if orig_etcd is not None:
+                os.environ["ETCD_ENDPOINTS"] = orig_etcd
+            else:
+                os.environ.pop("ETCD_ENDPOINTS", None)
+
+
+@pytest.fixture(scope="module")
+def tool_calling_services(
+    request, runtime_services, predownload_models
+) -> Generator[int, None, None]:
+    """Start the SGLang worker + tool-calling-aware frontend.
+
+    Yields the frontend HTTP port.
+    """
+    frontend_port, system_port = allocate_ports(count=2, start_port=10000)
+
+    with WorkerProcess(request, system_port=system_port):
+        # Allow worker to register with discovery.
+        time.sleep(2)
+        with ToolCallingFrontendProcess(request, frontend_port=frontend_port):
+            logger.info(
+                "Tool calling stack ready (frontend=%d worker_system=%d)",
+                frontend_port,
+                system_port,
+            )
+            yield frontend_port
+
+
+@pytest.fixture(scope="module")
+def client(tool_calling_services: int) -> OpenAI:
+    return OpenAI(
+        api_key="EMPTY", base_url=f"http://localhost:{tool_calling_services}/v1"
+    )
+
+
+@pytest.fixture(scope="module")
+def model() -> str:
+    return MODEL_NAME
+
+
+# ---------------------------------------------------------------------------
+# Tool definitions
+# ---------------------------------------------------------------------------
+
+TOOLS_WEATHER = [
+    {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get the current weather for a city",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "city": {"type": "string"},
+                    "unit": {
+                        "type": "string",
+                        "enum": ["celsius", "fahrenheit"],
+                    },
+                },
+                "required": ["city"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+TOOLS_SEARCH = [
+    {
+        "type": "function",
+        "function": {
+            "name": "search_web",
+            "description": "Search the web for information",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "query": {"type": "string"},
+                    "num_results": {"type": "integer"},
+                },
+                "required": ["query"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+TOOLS_CALCULATOR = [
+    {
+        "type": "function",
+        "function": {
+            "name": "calculate",
+            "description": "Evaluate a mathematical expression",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "expression": {"type": "string"},
+                },
+                "required": ["expression"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+TOOLS_COMPLEX_ARGS = [
+    {
+        "type": "function",
+        "function": {
+            "name": "create_event",
+            "description": "Create a calendar event with attendees and recurrence",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "title": {"type": "string"},
+                    "start_time": {"type": "string"},
+                    "end_time": {"type": "string"},
+                    "attendees": {
+                        "type": "array",
+                        "items": {
+                            "type": "object",
+                            "properties": {
+                                "name": {"type": "string"},
+                                "email": {"type": "string"},
+                                "role": {
+                                    "type": "string",
+                                    "enum": ["required", "optional", "organizer"],
+                                },
+                            },
+                            "required": ["email"],
+                            "additionalProperties": True,
+                        },
+                    },
+                    "recurrence": {
+                        "type": "object",
+                        "properties": {
+                            "frequency": {
+                                "type": "string",
+                                "enum": ["daily", "weekly", "monthly"],
+                            },
+                            "interval": {"type": "integer"},
+                            "count": {"type": "integer"},
+                        },
+                        "additionalProperties": True,
+                    },
+                    "location": {"type": "string"},
+                    "description": {"type": "string"},
+                },
+                "required": ["title", "start_time", "end_time"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+TOOLS_DATABASE = [
+    {
+        "type": "function",
+        "function": {
+            "name": "query_database",
+            "description": "Execute a SQL query against the database",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "sql": {"type": "string"},
+                    "params": {
+                        "type": "array",
+                        "items": {"type": "string"},
+                    },
+                    "database": {
+                        "type": "string",
+                        "enum": ["users", "orders", "products"],
+                    },
+                },
+                "required": ["sql", "database"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+TOOLS_GET_TIME = [
+    {
+        "type": "function",
+        "function": {
+            "name": "get_time",
+            "description": "Get the current time in a timezone",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "timezone": {"type": "string"},
+                },
+                "required": ["timezone"],
+                "additionalProperties": True,
+            },
+        },
+    }
+]
+
+ALL_TOOLS = (
+    TOOLS_WEATHER
+    + TOOLS_SEARCH
+    + TOOLS_CALCULATOR
+    + TOOLS_COMPLEX_ARGS
+    + TOOLS_DATABASE
+)
+
+
+# ---------------------------------------------------------------------------
+# Streaming helpers
+# ---------------------------------------------------------------------------
+
+
+def tool_schema_map(tools: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
+    out: dict[str, dict[str, Any]] = {}
+    for tool in tools:
+        fn = tool["function"]
+        out[fn["name"]] = fn["parameters"]
+    return out
+
+
+@dataclass
+class StreamResult:
+    content: str
+    reasoning_content: str
+    tool_calls: list[dict[str, Any]]
+    finish_reason: str | None
+    model: str
+    chunks: int
+    ttft_ms: float
+    raw_chunks: list[Any]
+
+
+def collect_stream(stream) -> StreamResult:
+    content_parts: list[str] = []
+    reasoning_parts: list[str] = []
+    tool_calls_by_index: dict[int, dict[str, Any]] = {}
+    finish_reason = None
+    model = ""
+    chunk_count = 0
+    raw_chunks: list[Any] = []
+    t0 = time.monotonic()
+    ttft_ms = 0.0
+
+    for chunk in stream:
+        raw_chunks.append(chunk)
+        chunk_count += 1
+        if chunk_count == 1:
+            ttft_ms = (time.monotonic() - t0) * 1000.0
+        model = chunk.model
+
+        for choice in chunk.choices:
+            delta = choice.delta
+
+            if getattr(delta, "content", None):
+                content_parts.append(delta.content)
+
+            if getattr(delta, "reasoning_content", None):
+                reasoning_parts.append(delta.reasoning_content)
+
+            if getattr(delta, "tool_calls", None):
+                for tc in delta.tool_calls:
+                    idx = tc.index
+                    entry = tool_calls_by_index.setdefault(
+                        idx,
+                        {
+                            "id": "",
+                            "type": "function",
+                            "function": {"name": "", "arguments": ""},
+                        },
+                    )
+
+                    if tc.id:
+                        if entry["id"] and entry["id"] != tc.id:
+                            raise AssertionError(
+                                f"Tool call id changed within same index {idx}: "
+                                f"{entry['id']} -> {tc.id}"
+                            )
+                        entry["id"] = tc.id
+
+                    if tc.type:
+                        entry["type"] = tc.type
+
+                    if tc.function:
+                        if tc.function.name:
+                            if (
+                                entry["function"]["name"]
+                                and entry["function"]["name"] != tc.function.name
+                            ):
+                                raise AssertionError(
+                                    f"Tool name changed within same index {idx}: "
+                                    f"{entry['function']['name']} -> {tc.function.name}"
+                                )
+                            entry["function"]["name"] = tc.function.name
+
+                        if tc.function.arguments:
+                            entry["function"]["arguments"] += tc.function.arguments
+
+            if choice.finish_reason:
+                finish_reason = choice.finish_reason
+
+    ordered_tool_calls = [tool_calls_by_index[i] for i in sorted(tool_calls_by_index)]
+    return StreamResult(
+        content="".join(content_parts),
+        reasoning_content="".join(reasoning_parts),
+        tool_calls=ordered_tool_calls,
+        finish_reason=finish_reason,
+        model=model,
+        chunks=chunk_count,
+        ttft_ms=ttft_ms,
+        raw_chunks=raw_chunks,
+    )
+
+
+def stream_chat(
+    client: OpenAI,
+    model: str,
+    *,
+    messages: list[dict[str, Any]],
+    tools: list[dict[str, Any]] | None = None,
+    max_tokens: int = 4096,
+    **kwargs,
+) -> StreamResult:
+    req: dict[str, Any] = {
+        "model": model,
+        "messages": messages,
+        "stream": True,
+        "max_tokens": max_tokens,
+    }
+    if tools is not None:
+        req["tools"] = tools
+    req.update(kwargs)
+    stream = client.chat.completions.create(**req)
+    return collect_stream(stream)
+
+
+def parse_and_validate_tool_call(
+    tc: dict[str, Any],
+    schema_by_name: dict[str, dict[str, Any]],
+    *,
+    expected_name: str | None = None,
+) -> dict[str, Any]:
+    assert tc["type"] == "function", f"unexpected tool type: {tc['type']!r}"
+    assert tc["id"], "tool call id must be non-empty"
+    fn_name = tc["function"]["name"]
+    assert fn_name, "tool call function name must be non-empty"
+
+    if expected_name is not None:
+        assert fn_name == expected_name, f"expected {expected_name!r}, got {fn_name!r}"
+
+    assert fn_name in schema_by_name, f"unknown tool name {fn_name!r}"
+    args_str = tc["function"]["arguments"]
+    assert args_str, "tool call arguments must be non-empty"
+
+    try:
+        args = json.loads(args_str)
+    except json.JSONDecodeError as e:
+        raise AssertionError(f"arguments are not valid JSON: {args_str!r}") from e
+
+    assert isinstance(args, dict), f"arguments must decode to object, got {type(args)}"
+
+    validator = Draft7Validator(schema_by_name[fn_name])
+    errors = sorted(validator.iter_errors(args), key=lambda e: list(e.path))
+    if errors:
+        rendered = "; ".join(
+            f"path={list(err.path)} message={err.message}" for err in errors
+        )
+        raise AssertionError(f"arguments failed schema validation: {rendered}")
+
+    return args
+
+
+def assert_finish_reason(result: StreamResult, allowed: set[str]) -> None:
+    assert result.finish_reason in allowed, (
+        f"unexpected finish_reason={result.finish_reason!r}, "
+        f"allowed={sorted(allowed)}"
+    )
+
+
+def assistant_tool_message_from_result(result: StreamResult) -> dict[str, Any]:
+    return {
+        "role": "assistant",
+        "content": result.content or None,
+        "tool_calls": result.tool_calls,
+    }
+
+
+# ---------------------------------------------------------------------------
+# Protocol / contract tests
+# ---------------------------------------------------------------------------
+
+
+class TestToolCallingProtocol:
+    def test_stream_has_required_chunk_shape(self, client: OpenAI, model: str):
+        stream = client.chat.completions.create(
+            model=model,
+            messages=[{"role": "user", "content": "What's the weather in Berlin?"}],
+            tools=TOOLS_WEATHER,
+            stream=True,
+            max_tokens=256,
+        )
+
+        chunk_count = 0
+        saw_finish = False
+        for chunk in stream:
+            chunk_count += 1
+            assert chunk.id
+            assert chunk.model == model or isinstance(chunk.model, str)
+            assert chunk.object == "chat.completion.chunk"
+            assert chunk.created > 0
+            assert len(chunk.choices) >= 1
+
+            for choice in chunk.choices:
+                assert choice.index == 0
+                if choice.finish_reason is not None:
+                    saw_finish = True
+                    assert choice.finish_reason in {"stop", "tool_calls", "length"}
+
+        assert chunk_count > 0
+        assert saw_finish, "stream never emitted a finish_reason"
+
+    def test_single_tool_call_schema_valid(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "What's the weather in Tokyo?"}],
+            tools=TOOLS_WEATHER,
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        assert len(result.tool_calls) >= 1
+
+        schema = tool_schema_map(TOOLS_WEATHER)
+        args = parse_and_validate_tool_call(
+            result.tool_calls[0], schema, expected_name="get_weather"
+        )
+        assert "city" in args
+        assert isinstance(args["city"], str)
+        assert args["city"]
+
+    def test_tool_choice_required_forces_a_tool_call(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "Hello there."}],
+            tools=TOOLS_WEATHER,
+            tool_choice="required",
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        assert len(result.tool_calls) >= 1
+        # Intent of this test: verify tool_choice=required forces a call.
+        # The prompt doesn't warrant a tool call, so a small model may
+        # hallucinate values for optional fields.  Validate only that the
+        # call is well-formed and the required fields are present; don't
+        # enforce the full schema (e.g. enum values on optional fields).
+        schema = tool_schema_map(TOOLS_WEATHER)
+        for tc in result.tool_calls:
+            assert tc["type"] == "function"
+            assert tc["id"]
+            fn_name = tc["function"]["name"]
+            assert fn_name in schema, f"unknown tool name {fn_name!r}"
+            args = json.loads(tc["function"]["arguments"])
+            assert isinstance(args, dict)
+            for required_field in schema[fn_name].get("required", []):
+                assert (
+                    required_field in args
+                ), f"{fn_name} missing required field {required_field!r}"
+
+    def test_tool_choice_none_suppresses_tool_calls(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "What's the weather in Paris?"}],
+            tools=TOOLS_WEATHER,
+            tool_choice="none",
+        )
+        assert_finish_reason(result, {"stop"})
+        assert result.tool_calls == []
+        assert result.content.strip()
+
+    def test_named_tool_choice_forces_specific_function(
+        self, client: OpenAI, model: str
+    ):
+        result = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "What's the weather in Paris?"}],
+            tools=TOOLS_WEATHER,
+            tool_choice={"type": "function", "function": {"name": "get_weather"}},
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        assert len(result.tool_calls) >= 1
+        schema = tool_schema_map(TOOLS_WEATHER)
+        for tc in result.tool_calls:
+            parse_and_validate_tool_call(tc, schema, expected_name="get_weather")
+
+    def test_parallel_multi_tool_request_includes_all_expected_tools(
+        self, client: OpenAI, model: str
+    ):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": (
+                        "Do all three of these with tools: "
+                        "1) weather in Paris, "
+                        "2) search the web for latest Python release, "
+                        "3) calculate 15 * 23 + 7."
+                    ),
+                }
+            ],
+            tools=TOOLS_WEATHER + TOOLS_SEARCH + TOOLS_CALCULATOR,
+            parallel_tool_calls=True,
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        # Models sometimes batch only a subset and emit follow-up calls in
+        # later turns; require at least 2 distinct tools rather than all 3.
+        schemas = tool_schema_map(TOOLS_WEATHER + TOOLS_SEARCH + TOOLS_CALCULATOR)
+        names: set[str] = set()
+        for tc in result.tool_calls:
+            parse_and_validate_tool_call(tc, schemas)
+            names.add(tc["function"]["name"])
+        assert len(names) >= 2, f"expected at least 2 distinct tools, got {names}"
+
+    def test_tool_call_ids_unique_in_single_response(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": "Get weather for New York, London, and Tokyo.",
+                }
+            ],
+            tools=TOOLS_WEATHER,
+            tool_choice="required",
+            parallel_tool_calls=True,
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        ids = [tc["id"] for tc in result.tool_calls]
+        assert len(ids) == len(set(ids)), f"duplicate tool ids: {ids}"
+
+    def test_complex_nested_arguments_schema_valid(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": (
+                        "Create a weekly team standup meeting titled 'Engineering Standup' "
+                        "from 2025-01-15T09:00:00Z to 2025-01-15T09:30:00Z. "
+                        "Add attendees: Alice (alice@example.com, required) and "
+                        "Bob (bob@example.com, optional). "
+                        "Set recurrence weekly every 1 week for 10 occurrences. "
+                        "Location: Conference Room B. "
+                        "Use the create_event tool."
+                    ),
+                }
+            ],
+            tools=TOOLS_COMPLEX_ARGS,
+        )
+        if result.finish_reason != "tool_calls":
+            pytest.skip(
+                "Model declined to call create_event for complex schema "
+                f"(finish_reason={result.finish_reason!r})"
+            )
+        schema = tool_schema_map(TOOLS_COMPLEX_ARGS)
+        args = parse_and_validate_tool_call(
+            result.tool_calls[0], schema, expected_name="create_event"
+        )
+        assert args["title"]
+        assert args["start_time"]
+        assert args["end_time"]
+        assert isinstance(args.get("attendees", []), list)
+
+    def test_sql_tool_arguments_schema_valid(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": (
+                        "Call the query_database tool. "
+                        "Set the 'database' parameter to \"users\" and "
+                        "set the 'sql' parameter to: "
+                        "SELECT * FROM users WHERE name LIKE '%O''Brien%' "
+                        "AND created_at > '2024-01-01'"
+                    ),
+                }
+            ],
+            tools=TOOLS_DATABASE,
+            tool_choice={"type": "function", "function": {"name": "query_database"}},
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        schema = tool_schema_map(TOOLS_DATABASE)
+        args = parse_and_validate_tool_call(
+            result.tool_calls[0], schema, expected_name="query_database"
+        )
+        assert args["database"] == "users"
+        assert "SELECT" in args["sql"].upper()
+
+    def test_array_argument_schema_valid(self, client: OpenAI, model: str):
+        tools = [
+            {
+                "type": "function",
+                "function": {
+                    "name": "send_emails",
+                    "description": "Send emails",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {
+                            "recipients": {
+                                "type": "array",
+                                "items": {"type": "string"},
+                            },
+                            "subject": {"type": "string"},
+                            "body": {"type": "string"},
+                        },
+                        "required": ["recipients", "subject", "body"],
+                    },
+                },
+            }
+        ]
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": (
+                        "Send an email with subject 'Team Update' and body "
+                        "'Meeting at 3pm' to alice@example.com, bob@example.com, "
+                        "and carol@example.com."
+                    ),
+                }
+            ],
+            tools=tools,
+            tool_choice={"type": "function", "function": {"name": "send_emails"}},
+        )
+        assert_finish_reason(result, {"tool_calls"})
+        schema = tool_schema_map(tools)
+        args = parse_and_validate_tool_call(
+            result.tool_calls[0], schema, expected_name="send_emails"
+        )
+        assert isinstance(args["recipients"], list)
+        assert len(args["recipients"]) >= 3
+
+    def test_no_tools_is_plain_text(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "What is the capital of France?"}],
+        )
+        assert_finish_reason(result, {"stop"})
+        assert result.tool_calls == []
+        assert result.content.strip()
+
+
+# ---------------------------------------------------------------------------
+# Multi-turn contract tests
+# ---------------------------------------------------------------------------
+
+
+class TestToolCallingMultiTurn:
+    def test_tool_result_is_consumed_and_final_answer_is_text(
+        self, client: OpenAI, model: str
+    ):
+        schemas = tool_schema_map(TOOLS_WEATHER)
+
+        first = stream_chat(
+            client,
+            model,
+            messages=[{"role": "user", "content": "What is the weather in London?"}],
+            tools=TOOLS_WEATHER,
+        )
+        assert_finish_reason(first, {"tool_calls"})
+        assert len(first.tool_calls) >= 1
+        parse_and_validate_tool_call(
+            first.tool_calls[0], schemas, expected_name="get_weather"
+        )
+
+        second = stream_chat(
+            client,
+            model,
+            messages=[
+                {"role": "user", "content": "What is the weather in London?"},
+                assistant_tool_message_from_result(first),
+                {
+                    "role": "tool",
+                    "tool_call_id": first.tool_calls[0]["id"],
+                    "content": json.dumps(
+                        {"temperature": 15, "unit": "celsius", "condition": "cloudy"}
+                    ),
+                },
+            ],
+            tools=TOOLS_WEATHER,
+        )
+        assert_finish_reason(second, {"stop"})
+        assert second.tool_calls == []
+        assert second.content.strip()
+        assert "15" in second.content or "cloud" in second.content.lower()
+
+    def test_chained_tool_use_search_then_calculate(self, client: OpenAI, model: str):
+        schemas = tool_schema_map(TOOLS_SEARCH + TOOLS_CALCULATOR)
+        messages: list[dict[str, Any]] = [
+            {
+                "role": "user",
+                "content": (
+                    "Search the web for the population of Tokyo, "
+                    "then calculate what 10% of that number is."
+                ),
+            }
+        ]
+
+        step1 = stream_chat(
+            client, model, messages=messages, tools=TOOLS_SEARCH + TOOLS_CALCULATOR
+        )
+        assert_finish_reason(step1, {"tool_calls"})
+        assert len(step1.tool_calls) >= 1
+        parse_and_validate_tool_call(step1.tool_calls[0], schemas)
+
+        messages.append(assistant_tool_message_from_result(step1))
+        messages.append(
+            {
+                "role": "tool",
+                "tool_call_id": step1.tool_calls[0]["id"],
+                "content": json.dumps(
+                    {
+                        "results": [
+                            {"title": "Tokyo population", "snippet": "13,960,000"}
+                        ]
+                    }
+                ),
+            }
+        )
+
+        step2 = stream_chat(
+            client, model, messages=messages, tools=TOOLS_SEARCH + TOOLS_CALCULATOR
+        )
+        # Small models sometimes short-circuit and compute the answer in
+        # their reasoning instead of chaining a second tool call. Accept
+        # either path: (a) another tool call to `calculate`, or (b) a
+        # direct text answer containing the correct result.
+        assert_finish_reason(step2, {"tool_calls", "stop"})
+        if step2.finish_reason == "tool_calls":
+            assert len(step2.tool_calls) >= 1
+            args2 = parse_and_validate_tool_call(step2.tool_calls[0], schemas)
+            assert step2.tool_calls[0]["function"]["name"] == "calculate"
+            assert "13960000" in args2["expression"].replace(
+                ",", ""
+            ) or "1396000" in args2["expression"].replace(",", "")
+
+            messages.append(assistant_tool_message_from_result(step2))
+            messages.append(
+                {
+                    "role": "tool",
+                    "tool_call_id": step2.tool_calls[0]["id"],
+                    "content": "1396000",
+                }
+            )
+
+            step3 = stream_chat(
+                client, model, messages=messages, tools=TOOLS_SEARCH + TOOLS_CALCULATOR
+            )
+            assert_finish_reason(step3, {"stop"})
+            assert step3.tool_calls == []
+            assert "1396000" in step3.content.replace(",", "")
+        else:
+            # Short-circuit path: model did the math itself. Just verify
+            # the final answer is present in the text.
+            assert step2.tool_calls == []
+            assert "1396000" in step2.content.replace(",", "")
+
+    def test_multiple_prior_tool_results_synthesize_to_text(
+        self, client: OpenAI, model: str
+    ):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {"role": "user", "content": "Get the weather in Tokyo and Paris."},
+                {
+                    "role": "assistant",
+                    "content": None,
+                    "tool_calls": [
+                        {
+                            "id": "call_001",
+                            "type": "function",
+                            "function": {
+                                "name": "get_weather",
+                                "arguments": json.dumps({"city": "Tokyo"}),
+                            },
+                        },
+                        {
+                            "id": "call_002",
+                            "type": "function",
+                            "function": {
+                                "name": "get_weather",
+                                "arguments": json.dumps({"city": "Paris"}),
+                            },
+                        },
+                    ],
+                },
+                {
+                    "role": "tool",
+                    "tool_call_id": "call_001",
+                    "content": json.dumps(
+                        {"temperature": 22, "unit": "celsius", "condition": "sunny"}
+                    ),
+                },
+                {
+                    "role": "tool",
+                    "tool_call_id": "call_002",
+                    "content": json.dumps(
+                        {"temperature": 18, "unit": "celsius", "condition": "rainy"}
+                    ),
+                },
+            ],
+            tools=TOOLS_WEATHER,
+        )
+        assert_finish_reason(result, {"stop"})
+        assert result.tool_calls == []
+        assert result.content.strip()
+        lower = result.content.lower()
+        assert "tokyo" in lower or "paris" in lower
+
+
+# ---------------------------------------------------------------------------
+# Model-behavior smoke tests
+# These are intentionally looser because the model may vary.
+# ---------------------------------------------------------------------------
+
+
+class TestToolCallingModelBehavior:
+    def test_many_tools_prefers_calculator_for_math_question(
+        self, client: OpenAI, model: str
+    ):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {"role": "user", "content": "What is 2^10? Use a tool if helpful."}
+            ],
+            tools=ALL_TOOLS,
+        )
+        assert result.finish_reason in {"stop", "tool_calls"}
+        if result.finish_reason == "tool_calls":
+            assert len(result.tool_calls) >= 1
+            assert result.tool_calls[0]["function"]["name"] == "calculate"
+
+    def test_unicode_arguments_are_preserved(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "user",
+                    "content": "What's the weather in Zürich, Switzerland?",
+                }
+            ],
+            tools=TOOLS_WEATHER,
+        )
+        assert result.finish_reason in {"stop", "tool_calls"}
+        if result.finish_reason == "tool_calls":
+            schema = tool_schema_map(TOOLS_WEATHER)
+            args = parse_and_validate_tool_call(
+                result.tool_calls[0], schema, expected_name="get_weather"
+            )
+            assert args["city"]
+
+    def test_system_instruction_encourages_tool_use(self, client: OpenAI, model: str):
+        result = stream_chat(
+            client,
+            model,
+            messages=[
+                {
+                    "role": "system",
+                    "content": (
+                        "You are a careful weather assistant. "
+                        "Always use the get_weather tool for weather questions."
+                    ),
+                },
+                {"role": "user", "content": "How's the weather in Sydney?"},
+            ],
+            tools=TOOLS_WEATHER,
+        )
+        assert result.finish_reason in {"stop", "tool_calls"}
+        if result.finish_reason == "tool_calls":
+            schema = tool_schema_map(TOOLS_WEATHER)
+            parse_and_validate_tool_call(
+                result.tool_calls[0], schema, expected_name="get_weather"
+            )