Twin of billion-context#684: reasoning-drop needs a strict-echo gate (DeepSeek thinking mode)

[ranxianglei]

The adapter's #651 twin (src/reasoning-drop.ts, drop:true default) strips the reasoning run preceding a closed compress call — on strict-echo thinking upstreams (DeepSeek: reasoning_content must be passed back when tools are in play) that produces the same HTTP 400 fixed in billion-context#690 (proxy side) + acp-kernel#245 (fold atomicity).

The kernel-side fix protects the fold split for every host, but the pi-side DROP itself has no strictness gate. Suggested: port isStrictReasoningEcho() (static deepseek host check from the provider baseUrl + learned flag), or at minimum document compress.reasoning.drop:false for DeepSeek/GLM-thinking/QwQ provider configs.

Depends on acp-kernel 0.0.63 (turn-integrity) for the full closure; pin bump will come with the next release PR.

[ranxianglei]

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Verified and fixed — PR #363.

Triage (审核先于实现)

1. Bug confirmed real. Cross-checked against the original report in billion-context#684, which documents the closed-compress reasoning DROP as a loss path independent of the fold split: after a single closed compress round, the rebuilt request independently reproduces the identical DeepSeek invalid_request_error (The reasoning_content in the thinking mode must be passed back to the API). The pi adapter's dropCompressReasoning() (default drop:true, src/reasoning-drop.ts) strips exactly that run, with zero provider awareness.

2. Layering. Symptom = HTTP 400 on the request after a closed compress turn. Root cause = the drop pass has no strictness gate — it runs unconditionally on every host. The kernel fix (acp-kernel#245) protects the fold split, and the proxy fix (billion-context#690) covers only the proxy host; neither reaches this pi DROP path, so it needed its own gate.

3. Solution — ported the sibling detector, adapted to pi's signals. New pure isStrictReasoningEcho(provider?, baseUrl?) (static DeepSeek check from ctx.model.baseUrl / provider name, case-insensitive substring) + applyStrictReasoningGate(...), wired into runtime.reasoningDropFor(ctx). On a strict-echo upstream it forces drop:false regardless of config (safety wins over an explicit drop:true); cost-free for non-thinking models on those hosts (they emit no thinking parts). Logs compress-reasoning-auto-disabled once per session.

   • Why static-only, no learned flag: the in-process adapter does not own the HTTP layer — Pi makes the LLM call and no extension hook observes the upstream 400, so the proxy's learn-on-400 self-heal isn't observable here. Compensated with the documented manual override.
   • GLM-thinking / QwQ / self-hosted mirrors are deliberately not auto-detected (auto-detection would disable the pass for their non-thinking models); they keep the compress.providers.<name>.reasoning.drop:false escape hatch, now documented in CONFIGURATION.md (+zh-CN). That valve already existed since reasoning-drop never fires in single-user-message marathon sessions (closed-turn gate unreachable) #348 — the docs just make it discoverable.

Scope & deps. 6 files: src/reasoning-drop.ts, src/runtime.ts, tests/reasoning-drop.test.ts, CHANGELOG.md, CONFIGURATION.md, CONFIGURATION.zh-CN.md. The change is orthogonal to #348's closed-round refactor (already on master) — the gate forces drop:false before closure detection ever runs. Does not bump the acp-kernel pin (stays at master's 0.0.62); full closure pairs with acp-kernel 0.0.63 turn-integrity (#245), whose pin bump lands in the next release PR, as the issue notes. Verified locally: typecheck clean, 700 tests (697 pass / 0 fail / 3 skipped), build success.

中文摘要：已验证 bug 真实存在——DeepSeek 思考模式下，闭合 compress 轮次的 reasoning 被默认 drop:true 删除后，下一个请求独立复现同一个 400；根因是 pi 侧 drop pass 无上游严格性门控（内核 #245 只护折叠原子性、代理 #690 只护代理侧，都覆盖不到这里）。移植代理侧 #690 的静态 deepseek 检测并接入 runtime（进程内适配器不持有 HTTP 层，无法做 learn-on-400，故用静态检测 + 文档化手动逃生舱）；GLM-thinking/QwQ/自托管镜像刻意不做主机自动检测以免误伤其非思考模型，走手动 drop:false。未 bump acp-kernel（0.0.63 turn-integrity 随下个 release PR）。typecheck/测试(697 通过)/构建全绿。见 PR #363。