fix(openai-chat): prevent repeated history replay loops

[EmanueleCoppola]

Summary

• Prevent a degenerate Chat Completions assistant turn from priming subsequent requests with the same repeated output.
• Observed with opencode-go/deepseek-v4.1-flash (the configured OpenCode provider/model): one generation repeatedly emitted the same progress sentence. Replaying that full turn on the next request primed the repetition again.
• Collapse runs of three or more identical lines and complete repeated multi-line cycles only while replaying assistant history upstream. The response already shown to the client is unchanged.
• Add adapter-level coverage for the recorded 1,451-line case, repeated paragraphs, and ordinary assistant output.

Reproduction example

With opencode-go/deepseek-v4.1-flash, an assistant turn repeatedly emitted:

The external entry correctly inherits the native structural template while applying the provider's own context window. Let me verify native entries survive the merge unchanged.

The attached screenshot shows this sentence repeating within one generation. Before this change, the following request replayed the full repeated turn verbatim, which could amplify the loop.

Verification

• bun x tsc --noEmit — passed.
• bun test tests/adapters/adapter-usage.test.ts — 54 passed.
• Full suite was not run; this form is intentionally left unsubmitted for review.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed; none are needed for this internal replay safeguard.
• Security-sensitive surfaces were reviewed; this change does not touch secrets, authentication, or unsafe defaults.

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Summary by CodeRabbit

• Bug Fixes
  • Repeated assistant responses are now condensed before being sent upstream, reducing redundant text while preserving an indicator of how many repetitions occurred.
  • Repeated single-line and multi-line content is handled, including output with trailing line breaks and repeated message cycles.
  • Normal, non-repeated assistant responses remain unchanged.
  • Partial repetitions are preserved so that meaningful response content is not lost.

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Maintainers: @lidge-jun @Ingwannu

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📝 Walkthrough

Walkthrough

The change adds collapseRepeatedOutput and applies it to assistant text before OpenAI Chat message serialization. Tests cover repeated lines, repeated multi-line cycles, terminal newline preservation, partial cycles, and unchanged output.

Changes

Repeated output handling

Layer / File(s)	Summary
Repeated-output collapsing utility src/responses/repetition-breaker.ts	Adds bounded collapsing for repeated non-blank lines and eligible whole-message cycles. Collapsed output includes an [ocx: repeated N times in source output] marker.
OpenAI Chat integration and validation src/adapters/openai-chat.ts, tests/adapters/adapter-usage.test.ts	Applies collapseRepeatedOutput to assistant text before serialization. Tests cover repeated single lines, repeated multi-line blocks, terminal newlines, partial cycles, and unchanged ordinary output.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to adc74

The replay safeguard’s current cycle-handling behavior matches its tested contract, with no actionable merge-blocking issue remaining.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main change: preventing repeated assistant history from causing replay loops in the OpenAI Chat Completions adapter. This matches the implementation in…

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[lidge-jun]

리뷰 · 우선순위 61 / 80

이 PR은 Chat Completions로 올라가는 어시스턴트 히스토리가, 한 번 망가진 반복 출력을 그대로 다시 먹여서 다음 턴도 같은 문장을 내뿜는 루프를 끊습니다. 보고된 장면은 opencode-go/deepseek-v4.1-flash에서 한 생성 안에 같은 진행 문장이 수백~수천 줄 쌓인 뒤, 그 전체가 다음 요청의 어시스턴트 메시지로 재전송된 경우입니다. 클라이언트가 이미 본 응답은 그대로 두고, 업스트림으로 다시 보내는 히스토리만 줄입니다.

지금 dev(HEAD d08d11fb1, 패키지 2.55.0)의 src/adapters/openai-chat.ts messagesToChatFormat는 어시스턴트 텍스트를 textParts.map(...).join("")으로만 합칩니다. 반복 검사가 없습니다. 이 PR은 새 모듈 src/responses/repetition-breaker.ts의 collapseRepeatedOutput을 그 join 직후에 끼웁니다. 동작은 두 단계입니다. (1) 같은 줄이 연속 3회 이상이면 한 줄 + [ocx: repeated N times in source output] 마커로 줄입니다. (2) 줄 전체가 짧은 주기(최대 64줄)로 딱 나눠 떨어지면 한 주기만 남기고 같은 마커를 붙입니다. 공백만인 줄은 연속 붕괴 대상에서 빼고, 전체가 빈 줄인 주기도 건너뜁니다. 테스트는 1,451줄 단일 문장, 4회 반복 두 줄 문단, 그리고 2회만 반복된 정상 출력을 tests/adapters/adapter-usage.test.ts에 고정했습니다. bun x tsc --noEmit과 해당 테스트 54 pass를 로컬에서 돌렸다고 합니다.

현재 dev의 맨 위는 #4562(최종 어댑터 경계에서 손실 미디어 거부)라서 방향은 미디어 충실도 쪽입니다. 이 변경은 그 축과 겹치지 않는 독립 버그픽스입니다. OpenCode Go / DeepSeek v4 계열이 Chat 어댑터를 타는 경로에서 실제로 관측된 증폭이라, types/config 분리 캠페인과도 무관하고 close-don't-rebase 대상도 아닙니다. 범위가 좁고 회귀 테스트가 핵심 케이스를 잡아 점수는 중상입니다. 다만 “히스토리에 프록시 마커를 심는 설계”와 “Chat 어시스턴트 텍스트에만 적용”은 메인테이너가 한 번 선을 그어야 합니다.

라인 833 (openai-chat.ts) - 어시스턴트 text join 직후에만 collapseRepeatedOutput을 탑니다. 클라이언트로 나가는 스트림은 건드리지 않아서, “보이는 응답은 그대로 / 재전송만 줄인다”는 본문 주장이 코드와 맞습니다.
경로 src/responses/repetition-breaker.ts - 실제 호출처는 Chat 어댑터뿐인데 파일이 responses/ 아래에 있습니다. 이름·위치는 괜찮지만, Responses 경로나 다른 어댑터에는 아직 연결되지 않았다는 뜻입니다.
라인 MIN_REPETITIONS=3 - 같은 줄 2회는 그대로 두고 3회부터 접습니다. 테스트도 2회 반복을 보존해서, 정상적인 짧은 되풀이와 병적 루프를 구분합니다.
라인 collapseWholeMessageCycle - lines.length % period === 0일 때만 통째 주기를 접습니다. 주기가 중간에 끊긴 불완전 반복(예: 3.5바퀴)은 통째 붕괴가 안 되고, 연속 동일 줄 붕괴에만 의존합니다.
경로 thinking / reasoning_content - 같은 함수 안의 thinkingParts 합치기에는 붕괴가 없습니다. 텍스트만 돌고 사고가 반복되면 같은 증폭이 남을 수 있습니다.
경로 마커 문자열 - [ocx: repeated N times...]가 업스트림 컨텍스트에 그대로 들어갑니다. 토큰을 아끼고 루프를 끊는 데는 도움이 되지만, 모델이 이 문구를 따라 쓰거나 “내부 표식”을 학습할 여지는 있습니다. 조용히 truncate만 하는 대안과 비교가 필요합니다.
경로 줄바꿈 없는 장문 - 붕괴는 \n 기준입니다. 한 줄에 같은 문장이 공백만으로 이어지면 잡지 못합니다. 보고된 케이스는 줄 단위라 충분하지만, 한계는 알아 두세요.
경로 베이스 - dev 기준이고 미디어 가드(#4562)와 파일 충돌 가능성은 낮습니다. 그래도 머지 직전 adapter-usage와 Chat 관련 테스트를 한 번 더 돌리면 안전합니다.

메인테이너의 판단이 필요한 지점

• 업스트림 히스토리에 [ocx: repeated …] 마커를 남길지, 마커 없이 길이만 자를지
• Chat 어시스턴트 텍스트만이 아니라 reasoning_content/thinking, 그리고 Responses·다른 Chat-like 어댑터에도 같은 가드를 펼칠지
• src/responses/ 배치를 유지할지, 어댑터 전용이면 src/adapters/ 쪽으로 옮길지
• OpenCode Go DeepSeek 루프를 이 히스토리 가드만으로 충분한 완화로 볼지, 생성 중 조기 중단(스트림 쪽)도 따로 볼지

너의 추천
범위가 작고 재현·테스트가 분명하니, 마커 문구를 유지하기로 정했다면 dev에 리베이스 확인 후 tests/adapters/adapter-usage.test.ts 초록이면 머지하세요. thinking 경로와 Responses 확장은 후속 이슈로 열어 두고, 이번 PR은 Chat 재전송 루프만 막는 최소 패치로 들이는 편이 맞습니다. types/config 분리와는 무관하니 닫지 마세요.

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Inline comments:
In `@src/responses/repetition-breaker.ts`:
- Line 49: Update the repetition-processing flow around
collapseWholeMessageCycle to remove one trailing empty entry produced by
splitting text that ends with a newline, then restore the terminal newline after
joining the collapsed lines. Preserve behavior for text without a terminal
newline, and add the repeated “A\nB\n” regression case to the adapter tests.

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[Ingwannu]

Requesting changes on exact head adc746c925680dc168276263a8f0242d5ccec617; I do not think this approach is safe to merge.

messagesToChatFormat applies collapseRepeatedOutput to every replayed assistant message for every provider using openai-chat. Three identical lines or three short cycles are not protocol evidence of a degenerate generation. They can be legitimate CSV/table rows, generated code, test output, quoted transcripts, separators, or exact data the next turn must see. This patch deterministically deletes that content and injects an OCX-authored marker into the model-visible history. The partial-cycle rule changes meaning too: A/B/A/B/A/B/A becomes one cycle plus a count marker plus A.

The evidence names one opencode-go/deepseek-v4.1-flash generation, but the patch changes the shared adapter globally. That conflicts with the existing #3506 direction: the proxy must not infer semantic progress from prose. The current tests prove the heuristic executes; they do not make legitimate repeated content safe.

Please remove the unconditional replay rewrite. The next useful direction is to identify why the provider generated/replayed the repeated turn using content-free request/response and continuation diagnostics, then fix a structural translation or provider-specific contract. If a resource ceiling is independently needed, it should be an explicit byte/token retention boundary with honest truncation semantics, not a three-line semantic heuristic. I am intentionally not approving the contributor CI run for this head while this data-loss behavior remains.