fix(responses): drop legacy cache retention for GPT-5.6

[lilinxiong]

Summary

• Strip deprecated prompt_cache_retention from GPT-5.6 family Responses requests only on the ChatGPT forward-auth path.
• Keep API-key and custom OpenAI-compatible openai-responses passthroughs out of scope, preserving their caller-provided prompt_cache_retention unchanged.
• Preserve legacy retention passthrough for older models and preserve caller-provided prompt_cache_options without synthesizing a replacement TTL.
• Add focused coverage for the GPT-5.6 alias, Sol, Terra, Luna, legacy GPT-5.5 behavior, API-key custom endpoints, noncanonical forward endpoints, and pre-existing passthrough fixtures.
• Follow the current OpenAI GPT-5.6 migration guidance, which replaces prompt_cache_retention with prompt_cache_options.ttl while retaining implicit caching when options are omitted.

Verification

• bun test tests/openai-responses-passthrough.test.ts tests/anthropic-thinking-signature.test.ts — 90 pass, 0 fail
• bun run typecheck — passed
• bun run privacy:scan — passed
• CI-equivalent fresh-process general shards plus the storage-policy job, with all proxy environment variables removed — 13,409 pass, 10 skipped, 0 fail across 851 files
• Dedicated api-usage job, matching .github/workflows/ci.yml isolation — 24 pass, 0 fail
• Combined coverage — all 852 test files, 13,433 pass, 10 skipped, 0 fail
• git diff --check — passed

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed. No user configuration or workflow changed, so no docs update is required.
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults.

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Summary by CodeRabbit

• Bug Fixes
  • Improved compatibility with GPT-5.6 and its variants by removing the deprecated prompt cache retention setting from requests.
  • Preserved supported prompt cache options provided by callers.
  • Kept existing behavior unchanged for other models and unaffected requests.

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📝 Walkthrough

Walkthrough

The Responses adapter removes deprecated prompt_cache_retention from canonical forward-mode requests for GPT-5.6 model variants. Tests verify option preservation and unchanged behavior for key-auth custom and noncanonical forward endpoints.

Changes

GPT-5.6 prompt-cache compatibility

Layer / File(s)	Summary
Sanitize GPT-5.6 requests src/adapters/openai-responses.ts	stripDeprecatedPromptCacheRetention removes prompt_cache_retention for GPT-5.6 model IDs. Canonical forward-mode requests apply the sanitizer before normalization and serialization.
Validate prompt-cache behavior tests/openai-responses-passthrough.test.ts	Tests cover GPT-5.6 variants, preservation of caller-provided prompt_cache_options, and retention of prompt_cache_retention for key-auth custom and noncanonical forward endpoints.

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

Merge Risk: ⚪ Minimal · up to 82d63

The change is narrowly scoped to GPT-5.6 cache-retention handling, with legacy and passthrough behavior covered by the reported checks; no actionable merge-blocking risk remains.

Suggested reviewers: ingwannu, lidge-jun

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✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes removing legacy cache retention for GPT-5.6 Responses requests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

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Maintainers: @lidge-jun @Ingwannu @Wibias

[lidge-jun]

good

[lidge-jun]

Maintainer decision on the prompt_cache_retention collision (#2092).

Three PRs fix this three incompatible ways, so only one can land: #2091 (strip for every ChatGPT-backend Responses request), #2099 (startsWith("gpt-5.6"), forward path), and this one.

This PR is the one we want. Reasons, from reading all three diffs:

• The backend's cache handling is account-level and has provably varied by deployment — one deployment accepted "24h" and echoed it back. A global strip therefore fixes the report by removing a parameter that some accounts honor.
• Its predicate is the correct family boundary. modelId !== "gpt-5.6" && !modelId.startsWith("gpt-5.6-") cannot match an unrelated id like gpt-5.60, which startsWith("gpt-5.6") would.
• Declining to translate 24h into prompt_cache_options.ttl is right: GPT-5.6 uses a different TTL contract and implicit caching still applies when the caller sent no replacement. Inventing a translation is the one change here that could alter billing behavior.

One thing to fix before merge. stripDeprecatedPromptCacheRetention is called outside the if (forward) branch, so it also strips the field from API-key and third-party openai-responses passthroughs — not just the ChatGPT forward path this issue is about. That is defensible for genuine OpenAI endpoints, but the tests only exercise the forward-mode provider. Please add an API-key regression, and say explicitly whether custom OpenAI-compatible endpoints are in scope.

#2091 and #2099 will be closed as superseded once this lands.

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Actionable comments posted: 1

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Inline comments:
In `@src/adapters/openai-responses.ts`:
- Line 1508: Restrict the stripDeprecatedPromptCacheRetention call to canonical
OpenAI forward providers by gating it with
isCanonicalOpenAiForwardProvider(provider), preserving prompt_cache_retention
for custom forward endpoints; add regression coverage for the custom-forward
case.

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[lidge-jun]

Thanks for the key-auth commit — that closes the API-key half exactly as asked, and the new test is a real oracle (it fails against 72117f169, where the sanitizer ran unconditionally).

One thing left before this can merge, and it is the same shape as the original note rather than a new requirement.

forward is not "the ChatGPT backend". It is defined as provider.authMode === "forward" alone (src/adapters/openai-responses.ts:1483), and this repo explicitly supports noncanonical forward providers — a third-party gateway configured with authMode: "forward" and its own baseUrl. Those are exercised at tests/openai-responses-passthrough.test.ts:19-61.

So the current gate produces:

Provider	GPT-5.6 request
canonical ChatGPT forward	stripped — correct, this is #2092
custom endpoint, authMode: "forward"	stripped — not intended
API-key / custom endpoint	preserved — your fix
any non-GPT-5.6 model	preserved

The middle row is the remaining silent loss: a gateway that accepts prompt_cache_retention never sees it, purely because it authenticates by forwarding.

The fix is one call, and this file already makes the same argument 30 lines below yours:

// Same predicate as the routedCompaction gate in handleResponses(): an
// authMode check would let a noncanonical custom forward provider skip this
// rewrite while the server still routes it as a summarizer turn (#422).
if (parsed._compactionRequest === true && !isCanonicalOpenAiForwardProvider(provider)) {

isCanonicalOpenAiForwardProvider (src/providers/openai-tiers.ts:33) checks adapter + authMode + normalized base URL, and is already used in five places. Gating your sanitizer on it instead of on forward makes the strip mean "the backend that actually 400s".

A test for the custom-forward case would pin it — same shape as your key-auth test, but with authMode: "forward" and a non-ChatGPT baseUrl.

Everything else checked out: the predicate is correctly delimited (gpt-5.60 cannot match, unlike a raw startsWith), there is no scope creep, and there is no ordering conflict with stripUnsupportedForwardParams — the two remove disjoint keys.

[lidge-jun]

리뷰 · 우선순위 38 / 80

#2092의 prompt_cache_retention 충돌에서 메인테이너가 고른 패치다. GPT-5.6 패밀리 Responses 요청에서 레거시 필드를 빼되, 정규 ChatGPT forward에서만 뺀다. API 키·커스텀 OpenAI 호환·비정규 forward는 호출자 값을 유지한다. prompt_cache_options는 합성하지 않는다. 아이디어는 55쯤이다. 지금 점수는 38이다. 아직 draft이고 체크리스트가 2/4이며, Codex/CodeRabbit 정리와 “ready for review”가 비어 있다. hygiene는 통과했다.

구현은 src/adapters/openai-responses.ts다. stripDeprecatedPromptCacheRetention()은 modelId === "gpt-5.6" || modelId.startsWith("gpt-5.6-")일 때만 prompt_cache_retention을 제거한다. #2099의 맨앞 startsWith("gpt-5.6")보다 낫다. gpt-5.6foo 같은 앞글자 충돌을 피한다. 호출은 forward && isCanonicalOpenAiForwardProvider(provider) 안에서만 일어난다. 메인테이너가 남긴 “forward는 ChatGPT 백엔드가 아니다”에 대한 코드 답이 이미 들어 있다.

테스트가 그 경계를 고정한다. gpt-5.6 / sol / terra / luna에서 필드가 사라지고 prompt_cache_options는 안 생긴다. 호출자가 준 options는 남는다. gpt-5.5 기존 pin은 그대로다. key-auth 커스텀 엔드포인트와 비정규 authMode: "forward"는 "24h"를 유지한다. #2091(모든 forward에서 스트립)과 #2099(prefix만 보고 스트립)보다 이 범위가 dev의 계정/배포별 캐시 동작과 맞다.

남은 건 코드보다 게이트다. 설명 체크리스트가 아직 2/4이고 draft라서 리뷰-ready 라벨이 없다. 저자는 전체 스위트를 돌렸다고 썼다. 세 PR이 한 이슈를 고치므로 #2091·#2099는 이 머지 뒤에 닫히는 게 맞다. 보안 서피스는 아니다. 필드 하나를 정규 경로에서만 뺀다.

해결방안

코드는 이 점수에서 메인테이너가 이미 고른 방향이다. draft를 해제하고 체크리스트 나머지 두 칸을 채운 뒤 CI가 초록이면 머지하면 된다. #2091과 #2099는 이 PR이 랜 뒤에 close하고, 그 브랜치를 더 키우지 마라. prompt_cache_options.ttl로 번역하는 후속은 열지 마라. GPT-5.6 TTL 계약이 다르다고 이 diff가 이미 적었다.

이 댓글은 grok-bot이 작성했습니다

[lilinxiong]

Addressed the remaining provider-scope boundary in 00ad34403; the current PR head is 82d63bfcf after merging recent dev. The sanitizer now runs only for isCanonicalOpenAiForwardProvider(provider). API-key custom endpoints and noncanonical authMode: "forward" endpoints both retain prompt_cache_retention, with regressions for each. Local verification covers all 852 test files (13,433 pass, 10 skipped, 0 fail using the CI job topology), plus typecheck and privacy scan. The CodeRabbit thread is resolved and the PR is back to review-ready.

[lidge-jun]

Thanks for this, @lilinxiong — closing as superseded by #2138, which carries your implementation: the same stripDeprecatedPromptCacheRetention gated on isCanonicalOpenAiForwardProvider, and your decision not to translate the retired value into prompt_cache_options.

Of the three proposals for #2092, yours had the right contract. #2099 matched on a bare startsWith("gpt-5.6") and applied to any forward provider; #2091 stripped the field for every forward request and every model, which inverts the gpt-5.5 preserve pin at tests/openai-responses-passthrough.test.ts:807 — and the issue reporter had already withdrawn that broader claim.

One thing added on top: an explicit non-match test for gpt-5.60, so the family match cannot quietly widen later. Your work is credited in the PR description.

[lilinxiong]

Thanks for the clear comparison and for carrying the implementation forward in #2138. I appreciate the attribution and the added gpt-5.60 boundary test—it strengthens the exact family-match contract. Glad the narrower canonical ChatGPT scope was useful.