DeepSeek / Baidu Qianfan stream tool-call arguments in cumulative mode:
each chunk resends the full arguments-so-far instead of the new fragment.
The stream accumulator blindly concatenated arg deltas with +=, turning
that into '{...}{...}{...}', which failed json.loads and got nuked to '{}'
— a silently corrupted tool call (#35592). Worse on multi-param tools
(search_files, session_search, memory replace) because longer args take
more chunks, giving more resend opportunities.
- Per-slot cumulative latch in the stream accumulator: a delta that is a
strict superset of the accumulated buffer marks the slot cumulative and
replaces (not appends); exact duplicates are dropped only after latching.
Incremental fragments are untouched (default += path).
- Backstop _collapse_repeated_json_arguments() in the repair pipeline
collapses pure identical-resend buffers (K exact repeats of a valid-JSON
unit) for providers that resend the complete object from chunk 1. Only
reached after json.loads already failed, so compliant single objects are
never touched.
Not a gateway or DeepSeek-model bug — any OpenAI-wire provider in
cumulative streaming mode is affected.
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