fix(translation): open a reasoning summary part only when text streams - #671
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WalkthroughThe Responses stream encoder now opens reasoning summary parts only when text deltas arrive. Encrypted-only reasoning items omit summary-part events and complete with their encrypted content and an empty summary. A regression test and changelog entry document the behavior. ChangesResponses reasoning stream
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🟡 Moderate · up to An empty direct reasoning delta can still produce a summary-part-added event without its matching completion event, resulting in a malformed Responses stream for that input. This should be fixed before merge. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (1 skipped: 1 unsupported.)
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In `@crates/switchyard-translation/src/codecs/responses/stream.rs`:
- Line 843: In the reasoning-delta handling flow around
ensure_responses_reasoning_summary_started, avoid opening a summary part when
ReasoningDelta.text is empty; return after item initialization or guard the
helper call so only non-empty text starts a part. Add a regression test covering
a direct empty ReasoningDelta and verify no unmatched summary-part-added event
is emitted.
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CHANGELOG.mdcrates/switchyard-translation/src/codecs/responses/stream.rscrates/switchyard-translation/src/codecs/stream.rscrates/switchyard-translation/tests/stream_translation.rs
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The Responses stream encoder opened a summary part on every reasoning item, including encrypted-only items that never stream text, and closed it only when text had accumulated. An encrypted-only item therefore left the client with a reasoning_summary_part.added and no matching done, while the finished item carried an empty summary. The part now opens on the first text delta, so encrypted-only items open, carry their payload, and close with an empty summary and no part events. A stream test covers the encrypted-only case; the existing text case still sees its part open and close. Signed-off-by: Lin Jia <linj@nvidia.com>
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…elta An empty reasoning delta opened the item's summary part without adding text, and the part then never closed. The delta now only opens the item. Found by review; covered by a stream test. Signed-off-by: Lin Jia <linj@nvidia.com>
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Summary
The Responses stream encoder opened a
reasoning_summary_partfor every reasoning item as soon as the item opened, and closed it only when text had streamed. An encrypted-only reasoning item, which GPT-5 models return on every turn behind a route that re-streams a buffered reply, therefore left the client with aresponse.reasoning_summary_part.addedand no matchingdone, while the completed item carried an emptysummary. Clients tolerate it today, but it contradicts the shape the encoder itself emits for the completed item. Surfaced by review on #639 against an earlier revision of the codec; the condition still held on main after #646.Change
The summary part opens on the first non-empty text delta for the item instead of at item start. Encrypted-only items, and items whose provider sends an empty first delta, open, carry their payload, and close with an empty
summaryand no part events. Items with text see exactly the events they saw before:output_item.added,reasoning_summary_part.added,reasoning_summary_text.delta,reasoning_summary_text.done,reasoning_summary_part.done,output_item.done.Implementation: the per-item encoder state gains a
summary_startedflag;ensure_responses_reasoning_startednow emits only the item'saddedevent, and a newensure_responses_reasoning_summary_startedemits the part'saddedevent once, called from the text-delta path. An empty delta only opens the item.Tests
Two new stream tests: an encrypted-only reasoning detail produces no summary events and closes with the provider id, the payload, and an empty summary; an empty reasoning delta opens the item and no part. The existing summary-text test still sees its part open and close. Translation suite 185 tests, clippy clean with
-D warnings. Changelog entry under Unreleased.