[Bugfix] glm47 parser: tolerate missing opening <arg_value> tag

[drakosha]

Purpose

FIX #49248

Under concurrent load, GLM-4.7-family models sporadically skip the opening <arg_value> tag when emitting tool calls, producing

<tool_call>search<arg_key>query</arg_key>how many vacation days left</arg_value></tool_call>

with the argument value fully intact (raw sampled tokens captured via logprobs: true; reproduces at temperature: 0 too, ~5–17% of calls at concurrency 6 on our production trace family, 0 sequentially).

_ARG_RE/_PARTIAL_ARG_RE in vllm/parser/glm47_moe.py require the opening tag, so such calls silently parse to arguments: "{}", which then fails the client's tool schema validation and degrades agent loops (the broken {} call gets rendered back into history, so retries tend to fail the same way).

This PR makes the opening <arg_value> optional in both regexes. The closing </arg_value> still delimits the value, so:

• well-formed output parses exactly as before (the optional group matches the tag when present);
• streaming is unaffected: the incremental lexer buffers ambiguous tag prefixes, so a partially streamed <arg_value> never leaks into a value snapshot.

Test Plan

• tests/tool_parsers/test_glm47_moe_tool_parser.py: new non-streaming cases (single arg with missing opening tag; mixed malformed + well-formed args in one call) and a streaming case with the malformed sequence split across chunks; all pre-existing cases unchanged.
• Live validation on a 4×GPU GLM-5.2 deployment (--tool-call-parser glm47), replaying the production request that triggers the malformation at concurrency 6 with logprobs: true:
  • before: 12/120 responses parsed to arguments: "{}";
  • after: 12/72 responses still show the raw malformation in sampled tokens (model-side quirk, expected), all 12 parse to full arguments, 0 empty; streaming replay 0/72 empty.

Test Result

pytest tests/tool_parsers/test_glm47_moe_tool_parser.py — 16 passed.

[claude]

Claude Code Review

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[mergify]

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merged. Please rebase the PR, @drakosha.

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