fix: StreamingResponseAggregator drops/duplicates function calls in streaming mode - #6568
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fix: StreamingResponseAggregator drops/duplicates function calls in streaming mode#6568brucearctor wants to merge 1 commit into
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…treaming mode Fixes two issues in StreamingResponseAggregator that cause incorrect agent behavior when using StreamingMode.SSE with multi-agent workflows (transfer_to_agent + tools): 1. Progressive SSE path: close() could emit duplicate FunctionCall parts when streaming chunks overlap, causing the agent loop to re-execute the same tool call indefinitely. Fixed by deduplicating FC parts by their id in close(). 2. Legacy SSE path: close() only emitted text parts — FunctionCall parts received during streaming were silently dropped. This caused the agent loop to exit prematurely without executing tools. Fixed by tracking FC parts in _function_call_parts and including them in close(). Fixes google#6566
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Summary
Fixes two bugs in
StreamingResponseAggregatorthat cause incorrect agent behavior when usingStreamingMode.SSEwith multi-agent workflows (transfer_to_agent+ tools).Fixes #6566
Problem
Bug 1: Progressive SSE — Duplicate function call parts → infinite loop
close()could emit duplicateFunctionCallparts when streaming chunks overlap. This caused the agent loop inbase_llm_flow.run_asyncto re-execute the same tool call indefinitely (57+ LLM calls instead of 18).Bug 2: Legacy SSE — Function calls silently dropped → premature exit
close()only emitted text parts.FunctionCallparts received during streaming were silently dropped. The agent loop would exit prematurely without executing tools sinceis_final_response()saw no function calls.Fix
streaming_utils.pyProgressive path (
close()): DeduplicateFunctionCallparts by theiridbefore building the finalLlmResponse.Legacy path:
_function_call_partstracking inprocess_response()close()outputTests (
test_streaming_utils.py)test_progressive_close_deduplicates_function_calls: Verifies duplicate FC IDs are collapsedtest_legacy_close_preserves_function_calls: Verifies FCs survive legacy aggregationtest_pure_function_call_behavior_differs_by_modefor new legacy behaviorReproduction
Minimal repro script in #6566 — uses two agents +
transfer_to_agent+ tools to trigger the infinite loop.