OpenAI Response Deduplication — Investigation & Fix

Motivation

When using OpenAI models (gpt-4o, gpt-5-mini, gpt-5.2) through CAIPE, the chat UI shows human-readable text followed by a raw JSON blob and then the same text repeated. See architecture.md for the duplicated output example.

Root Cause

OpenAI's PlatformEngineerResponse structured output is streamed as plain message.content text, not as a tool call. The upstream agent.py in its post-stream parsing (PRIORITY 2 and 3 paths) calls handle_structured_response() but does not set from_response_format_tool = True on the resulting final_response dict.

This causes agent_executor.py to take the wrong code path (from_response_format_tool=False), falling back to _get_final_content() which joins all of supervisor_content — a mix of clean text and raw PlatformEngineerResponse JSON — producing duplicated output.

Why Bedrock/Claude are unaffected

Bedrock and Claude emit structured responses as tool calls, which are handled in the PRIORITY 1 path where from_response_format_tool is already correctly set to True. They never enter the PRIORITY 2/3 paths.

Key code locations

File	Path	What
agent.py	multi_agents/platform_engineer/protocol_bindings/a2a/agent.py	Streaming orchestration; PRIORITY 1/2/3 post-stream parsing
agent_executor.py	multi_agents/platform_engineer/protocol_bindings/a2a/agent_executor.py	Final content assembly; uses from_response_format_tool flag
response_format.py	multi_agents/platform_engineer/response_format.py	PlatformEngineerResponse Pydantic model
deep_agent.py	multi_agents/platform_engineer/deep_agent.py	USE_STRUCTURED_RESPONSE env var

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Testing Strategy

Models tested

Model	Prompt	Result
gpt-4o	"Weather in Allen, Texas"	Clean output, no JSON blobs
gpt-4o	"run network diagnostics on google.com"	Clean output, no duplication
gpt-5-mini	"Weather in Allen, Texas"	Clean output, no JSON blobs
gpt-5-mini	"run network diagnostics on google.com"	Clean output, no duplication
gpt-5.2	"Weather in Allen, Texas"	Clean output, no JSON blobs
gpt-5.2	"run network diagnostics on google.com"	Clean output, no duplication

Verification method

curl -s -X POST http://localhost:8000/ \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":"t","method":"message/send",
       "params":{"message":{"role":"user",
         "parts":[{"kind":"text","text":"Weather in Allen TX"}],
         "messageId":"t1"}}}' | python3 -c "
import sys, json
r = json.load(sys.stdin)
final = [a for a in r['result']['artifacts'] if a['name']=='final_result'][0]
text = ''.join(p['text'] for p in final['parts'] if p['kind']=='text')
has_json = '{\"status\"' in text
print('HAS RAW JSON:', has_json)
print(text[:500])
"

Expected: HAS RAW JSON: False

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Related

• Architecture: architecture.md