[Bugfix][Tool Parser] Fix hunyuan_a13b/xlam streaming: argument named "name" spawns a phantom tool call

[muhammadfawaz1]

Summary

In streaming mode, the hunyuan_a13b and xlam tool parsers treat any argument key "name" as the start of a new tool call. A tool call whose arguments contain a name field, a common shape, e.g. create_user(name=...), greet(name=...), is streamed as two tool calls: the real call with its arguments dropped, and a phantom tool call named after the argument's value. Non-streaming parsing of the same output is correct.

Root cause

Both parsers count/identify tool calls during streaming with a bare regex:

r'"name"\s*:\s*"([^"]+)"'

which matches the argument key "name" as well as a tool's own name field. This fix anchors the regex on the following "arguments" key so it only matches a tool's own name field:

r'"name"\s*:\s*"([^"]+)"(?=\s*,\s*"arguments"\s*:)'

xlam additionally had this pattern duplicated as inline string literals in two code paths; factored into a single self.tool_name_reg attribute, matching hunyuan_a13b's existing style.

Not a duplicate

• [Bug]: xlam and hunyuan_a13b tool parsers drop the arguments of any tool call that follows an empty-argument call (streaming) #47901 / [Bugfix][Frontend] Anchor empty-args detection to the current tool in xlam and hunyuan_a13b streaming parsers #47954 concern a different trigger — arguments dropped after an empty-argument call. [Bugfix][Frontend] Anchor empty-args detection to the current tool in xlam and hunyuan_a13b streaming parsers #47954 keeps the same unanchored "name"-matching regex, so it does not address this.
• [Bugfix][Tool Parser] Fix Hunyuan A13B nested JSON tool streaming #38103 reworks hunyuan's argument regexes for nested JSON (hunyuan only), not the "name" tool-detection regex; xlam is unaffected either way.

Test plan

• Added regression tests to both test_hunyuan_a13b_tool_parser.py and test_xlam_tool_parser.py covering the "name"-as-argument-key shape, non-streaming and streaming.
• python -m pytest tests/tool_parsers/test_hunyuan_a13b_tool_parser.py tests/tool_parsers/test_xlam_tool_parser.py -v — all relevant tests pass (1 pre-existing xfail, unrelated nested-JSON limitation, unchanged by this PR).
• pre-commit run --all-files on changed files: ruff check, ruff format, mypy all pass.

[claude]

Claude Code Review

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[chaunceyjiang]

If you discovered these two issues locally, I would suggest migrating these two parsers to the new Parser Engine instead of continuing to modify the old logic.

[muhammadfawaz1]

@chaunceyjiang Thanks for the pointer , I can see the new Parser Engine exists (gemma4/minimax_m2/nemotron_v3/qwen3 are on it), but I don't see an existing effort tracking migration of hunyuan_a13b/xlam to it. Is that migration something you'd want done as a prerequisite for this fix, or would it be fine to land this minimal correctness fix now and track the engine migration as separate follow-up work? Happy to help with the migration too if that's the preferred path and it's not already being planned by someone else.

[chaunceyjiang]

I think we should prioritize the migration. As far as I know, no one is currently working on it.

[muhammadfawaz1]

@chaunceyjiang Closing this PR, starting the migration instead. Two things I hit that I'd rather confirm than guess:

The 4 engine-based parsers (Qwen3, MiniMax M2, Gemma4, Nemotron V3) all use explicit per-call delimiters (<function=, <invoke name=", etc.) so the state machine knows where one tool call ends and the next begins. Hunyuan_a13b/xlam instead emit one undelimited JSON array ([{...},{...}]) — boundaries are just JSON commas/braces, no terminal token. Does the engine already support that shape, or does it need new engine-level work?

Hunyuan_a13b has a separate hunyuan_a13b_reasoning_parser.py (xlam doesn't). Since ParserEngine unifies reasoning + tool calls in one class, should the reasoning parser get folded in too, or stay separate?