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.
Pull the 10 pure sanitization/repair helpers (\_sanitize_surrogates,
\_sanitize_structure_surrogates, \_sanitize_messages_surrogates,
\_escape_invalid_chars_in_json_strings, \_repair_tool_call_arguments,
\_strip_non_ascii, \_sanitize_messages_non_ascii, \_sanitize_tools_non_ascii,
\_strip_images_from_messages, \_sanitize_structure_non_ascii) and the
\_SURROGATE_RE constant out of run_agent.py into a new module.
These are stateless byte-walking helpers with no AIAgent dependency.
Backward compatibility: run_agent re-exports every name via a single
import block, so existing 'from run_agent import _sanitize_surrogates'
imports in tests and cli.py keep working unchanged. Same pattern the
file already uses for _summarize_user_message_for_log (codex_responses_adapter).
run_agent.py: 16077 -> 15682 lines (-395).
