fix(openai-adapters): don't swallow stream chunks that carry usage - #1
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chatCompletionStream deferred any chunk with a `usage` field so that usage could be re-emitted after all content. That assumes usage appears only on a terminal chunk, which holds for the OpenAI API but not in general. llama.cpp-based servers can attach a running `usage` counter to every chunk. In that case the deferral branch matched on all of them, each overwriting lastChunkWithUsage, and only the final chunk was ever yielded — so the entire response was discarded and the assistant message rendered empty. Observed against a local orchestrator: 51 chunks in, 1 out, all reasoning_content and content deltas lost. Only defer chunks that are genuinely usage-only: usage present, no finish_reason, and an empty delta. Chunks carrying a payload are yielded immediately, and a usage-bearing content chunk clears the deferred chunk so it is not re-emitted as a duplicate. Tests cover both regimes (per-chunk running usage and OpenAI's terminal usage-only chunk) and are mutation-verified: reverting the predicate to `!!result.usage` fails them with empty content. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Pull request overview
This PR fixes OpenAIApi.chatCompletionStream so that streaming responses are not inadvertently withheld when providers attach a running usage object to every chunk (e.g. llama.cpp’s llama-server). It preserves the intent of reporting a terminal “usage-only” chunk last, while allowing normal content/reasoning chunks through immediately.
Changes:
- Adjusts usage deferral logic to defer only “usage-only” chunks (no
finish_reasonand emptydelta) instead of deferring any chunk that containsusage. - Adds regression tests covering (1) per-chunk running usage, (2) OpenAI’s terminal usage-only chunk behavior, and (3) avoiding duplicate trailing emission.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| packages/openai-adapters/src/apis/OpenAI.ts | Refines stream chunk deferral so content/reasoning chunks aren’t swallowed when usage appears on every chunk. |
| packages/openai-adapters/src/apis/OpenAIStreamUsage.test.ts | Adds targeted regression coverage for streaming usage edge-cases across OpenAI and llama.cpp-style servers. |
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ChangesOpenAI streaming usage
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: ⚪ Minimal · up to The change preserves streamed content when usage counters appear on each chunk and includes focused coverage for the supported formats; no actionable merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Pull request overview
Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.
Suppressed comments (2)
packages/openai-adapters/src/apis/OpenAI.ts:179
isUsageOnlyonly inspectsresult.choices?.[0]. Ifn > 1is used and the first choice happens to have an empty delta while another choice carries content/finish_reason, this will incorrectly treat the whole chunk as usage-only and defer it, dropping payload for the other choices. Consider determining “payload” across all choices instead of only index 0.
const choice = result.choices?.[0];
const isUsageOnly =
!!result.usage &&
!choice?.finish_reason &&
Object.keys(choice?.delta ?? {}).length === 0;
packages/openai-adapters/src/apis/OpenAIStreamUsage.test.ts:1
ChatCompletionChunkis only used as a type in this test file. Using a type-only import avoids emitting a runtime import (which can matter under ESM /verbatimModuleSyntax).
import { ChatCompletionChunk } from "openai/resources/index";
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Actionable comments posted: 2
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Inline comments:
In `@packages/openai-adapters/src/apis/OpenAI.ts`:
- Around line 175-179: Update the usage-only classification near result.choices
to evaluate every choice rather than only choices[0], so a chunk is usage-only
only when all choices lack a finish_reason and have empty deltas. Add a
regression test covering multiple choices where a later choice contains content
or a finish_reason, ensuring that payload is not deferred or dropped.
In `@packages/openai-adapters/src/apis/OpenAIStreamUsage.test.ts`:
- Around line 127-139: Update the test using apiYielding to prepend a usage-only
chunk before the two content-bearing chunks, then assert that the collected
output contains exactly the two content chunks and their combined content
remains “AB”.
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`isUsageOnly` inspected `choices[0]` only. With `n > 1`, a chunk whose first choice is empty but whose second carries content was classified as usage-only and deferred, dropping the other choice's payload. Use `every` across all choices instead. Also strengthens the duplicate-emission test: it began with a content-bearing chunk, so no deferred chunk ever existed and an implementation that failed to clear one would still have passed. It now opens with a usage-only chunk. Mutation-verified: the `n > 1` test fails against the old `choices[0]` logic, and the duplicate test fails when the clearing branch is removed. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Ports continuedev#13162 (filed upstream, which is read-only and will never merge it).
Description
chatCompletionStreamdeferred every chunk carrying ausageobject so usage could be reported last. That assumes the OpenAI convention whereusagearrives only on a terminal chunk.llama.cpp's
llama-serverattaches a runningusagecounter to every chunk (completion_tokens1, 2, 3…). Under that server the old condition matched all of them, so the entire stream was withheld and the user saw a blank reply.Only defer chunks that carry no payload — no
finish_reasonand an emptydelta.Tests
packages/openai-adapters/src/apis/OpenAIStreamUsage.test.ts, 3 cases: per-chunk running usage (llama.cpp), OpenAI terminal usage-only chunk, and no duplication. Mutation-verified — reverting the guard fails them. 87/87 adapter tests pass.Confirmed live against a real llama-server: content and reasoning both render.
Summary by CodeRabbit
Bug Fixes
Tests