fix(stream): handle audio completion markers

[HAYDEN-OAI]

• I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

• accumulate streamed chat-completion audio fields instead of replacing earlier id, data, and transcript fragments with each later delta
• allow finalChatCompletion() to finalize audio streams that end with a terminal expires_at-only chunk and no separate finish_reason
• keep the existing missing finish_reason error for non-audio, incomplete, malformed, or continued-after-expiry streams
• add regression coverage for the reported audio chunk sequence and the safety boundaries

Additional context & links

Fixes #1206.

gpt-4o-audio-preview can finish streaming with an audio delta containing only expires_at. The stream helper currently requires an explicit finish_reason, so finalChatCompletion() throws even though the audio response is complete. The existing generic delta merge also overwrites earlier audio fragments, leaving only the final audio object.

This change tracks whether the last meaningful choice delta is an expires_at-only audio completion marker and only infers finish_reason: stop when the accumulated audio has all required fields. It does not add a general missing-finish fallback.

Verification:

• pnpm test --runInBand tests/lib/ChatCompletionStream.test.ts
• pnpm lint
• pnpm test --runInBand

[openai-sdks]

OkTest Summary

✅ 237/237 SDK tests passed in 10.62s for Node SDK PR #1991.

Test results — 42 files

Test	Result	Time
tests/chat-completions-complex-body.test.ts	✅ Passed	151ms
tests/chat-completions-create.test.ts	✅ Passed	206ms
tests/chat-completions-stream.test.ts	✅ Passed	123ms
tests/files-content-binary.test.ts	✅ Passed	159ms
tests/files-create-multipart.test.ts	✅ Passed	159ms
tests/files-list-pagination.test.ts	✅ Passed	176ms
tests/initialize-config.test.ts	✅ Passed	171ms
tests/instance-isolation.test.ts	✅ Passed	105ms
tests/models-list.test.ts	✅ Passed	122ms
tests/responses-background-lifecycle.test.ts	✅ Passed	242ms
tests/responses-body-method-errors.test.ts	✅ Passed	357ms
tests/responses-cancel-timeout.test.ts	✅ Passed	252ms
tests/responses-cancel.test.ts	✅ Passed	208ms
tests/responses-compact-retries.test.ts	✅ Passed	224ms
tests/responses-compact.test.ts	✅ Passed	195ms
tests/responses-create-advanced-stream.test.ts	✅ Passed	111ms
tests/responses-create-advanced.test.ts	✅ Passed	311ms
tests/responses-create-disconnect.test.ts	✅ Passed	1.061s
tests/responses-create-errors.test.ts	✅ Passed	205ms
tests/responses-create-malformed-api-responses.test.ts	✅ Passed	141ms
tests/responses-create-retries.test.ts	✅ Passed	284ms
tests/responses-create-stream-failures.test.ts	✅ Passed	192ms
tests/responses-create-stream-timeout.test.ts	✅ Passed	2.183s
tests/responses-create-stream-wire.test.ts	✅ Passed	2.548s
tests/responses-create-stream.test.ts	✅ Passed	140ms
tests/responses-create-terminal-states.test.ts	✅ Passed	258ms
tests/responses-create-timeout.test.ts	✅ Passed	219ms
tests/responses-create.test.ts	✅ Passed	203ms
tests/responses-delete.test.ts	✅ Passed	236ms
tests/responses-input-items-errors.test.ts	✅ Passed	166ms
tests/responses-input-items-list.test.ts	✅ Passed	188ms
tests/responses-input-items-options.test.ts	✅ Passed	207ms
tests/responses-input-tokens-count-timeout.test.ts	✅ Passed	238ms
tests/responses-input-tokens-count.test.ts	✅ Passed	231ms
tests/responses-malformed-inputs.test.ts	✅ Passed	2.274s
tests/responses-not-found-errors.test.ts	✅ Passed	280ms
tests/responses-parse.test.ts	✅ Passed	169ms
tests/responses-retrieve-retries.test.ts	✅ Passed	274ms
tests/responses-retrieve.test.ts	✅ Passed	199ms
tests/responses-stored-method-errors.test.ts	✅ Passed	644ms
tests/retry-behavior.test.ts	✅ Passed	3.213s
tests/sdk-error-shape.test.ts	✅ Passed	295ms

View OkTest run #29772649840

_{SDK merge (c0d803b02d59) · head (5ee5d86efdb8) · base (39a15b412fc1) · OkTest (fd7a761c81c1)}

[jbeckwith-oai]

Reviewed head 5ee5d86. The audio fields are accumulated correctly, inferred completion is narrowly gated on a complete audio payload plus a terminal expires_at-only delta, and later deltas invalidate that marker. I also checked multi-choice behavior, explicit finish reasons, and incomplete audio. Local targeted tests, four additional boundary probes, the full test suite (1,198 passed), pnpm lint, and pnpm build all passed; GitHub CI is green.