Summary

Fixes #2550. OpenAI Responses streaming identifies response.function_call_arguments.delta and .done events with item_id, while the created function-call item carries the downstream call_id. Buffering by call_id therefore discarded valid argument events and caused MCPAgent.stream() to emit no tool-call steps.

The parser now buffers events by item_id (with call_id as a compatibility fallback), retains the function item\u0027s call_id for the ready payload and subsequent tool output, and rejects ambiguous/missing correlations instead of silently attaching data to a different call.

Design and boundaries

• item_id is the primary correlation key because it is the Responses event contract; call_id remains accepted for compatibility producers.
• The public tool-call payload still uses call_id, so driver/executor call sites keep their existing identity contract.
• This changes only streamed function-call argument correlation. It does not alter non-streaming response parsing or provider request formatting.

Validation

• pnpm exec vitest run src/llm/__tests__/openai-responses.test.ts — 9 passed
• pnpm run build — tsup build and declaration generation passed
• git diff --check origin/main...HEAD

The local Node is 22.16.0 while the workspace declares >=22.22.2; the focused tests and build completed despite that version warning. CI remains the full matrix.

Summary by cubic

Fixes OpenAI Responses streaming so tool argument events are correlated by item_id, restoring tool-call steps that MCPAgent.stream() previously dropped.

The parser now keys buffers by item_id, accepts call_id only when it uniquely identifies one output item, and drops unknown or ambiguous correlations instead of attaching data to the wrong call. The public tool-call payload still uses call_id, so driver/executor call sites keep their existing identity contract.

Bug Fixes

• Correlates streamed function-call argument events by item_id, with call_id accepted only for unambiguous compatibility producers.
• Preserves call_id in the public tool-call payload so driver/executor call sites keep their existing identity contract.

^{Written for commit ea58ab9. Summary will update on new commits.}