ranxianglei · ranxianglei · Sep 11, 2026 · Sep 10, 2026 · Sep 11, 2026 · Sep 11, 2026
diff --git a/CONFIGURATION.md b/CONFIGURATION.md
@@ -421,7 +421,7 @@ Environment variables take precedence over the config file. They are useful for
 | `ACP_LOG` | Set to `0` to disable request logging. |
 | `ACP_AUTO_UPDATE` | Set to `0` to disable auto-update checks. |
 | `ACP_UPDATE_TAG` | Dist-tag channel the auto-updater follows (default `latest`, e.g. `dev`). File-config key: `updateTag`. A `pr-N` preview tag is only followed when explicitly configured. |
-| `BILI_HOST_USAGE_CREDIT` | `#408` host-usage backfill mode (file-config key: `hostUsageCredit`). `auto` (default) = the uncompressed-baseline backfill is armed for plain proxy clients (the bili-launched pi/omp extensions are exempted — their host-side compaction is cancelled, so the baseline drives nothing there). `off` = never backfill — the usage reported to the host is the actually-forwarded (folded) request, matching `[acp-usage] input=`. Use `off` for plain anthropic proxy clients (e.g. ZCode) whose UI would otherwise show the cumulative, drifting baseline as inflated context (#648). |
+| ~~`BILI_HOST_USAGE_CREDIT`~~ / ~~`hostUsageCredit`~~ | **Removed in #660.** Used to select the host-facing usage mode. The #408 uncompressed-baseline backfill is gone entirely — every host now reports the actually-forwarded (post-fold) request as provider-measured (matches `[acp-usage] input=`). Old values left in env or the config file are ignored; remove them. See the "Bug history lesson" section of PR #691. |
 | `ACP_PROVIDERS` | Path to an external `providers.json` (legacy / shared file). |
 | `BILI_REPLAY_RETRY_BASE_MS` | Base backoff delay (ms) for acp-loop replay retries after a transient upstream rejection (default `1500`; set `0` to disable the delay). See #189. |
 | `BILI_REPLAY_RETRY_MAX` | Total attempts for acp-loop replay retries (default `3`; set `1` to disable retries entirely — legacy fail-fast behavior). See #189. |

diff --git a/CONFIGURATION.zh-CN.md b/CONFIGURATION.zh-CN.md
@@ -419,6 +419,7 @@
 | `ACP_LOG` | 设为 `0` 关闭请求日志。 |
 | `ACP_AUTO_UPDATE` | 设为 `0` 禁用自动更新检查。 |
 | `ACP_UPDATE_TAG` | 自动更新跟随的 dist-tag 通道（默认 `latest`，如 `dev`）。文件配置键：`updateTag`。`pr-N` 预览 tag 仅在显式配置时才会被跟随。 |
+| ~~`BILI_HOST_USAGE_CREDIT`~~ / ~~`hostUsageCredit`~~ | **#660 已移除。** 曾用于选择宿主可见的用量模式。#408 的未折叠基线回补（backfill）已整体删除 —— 所有宿主现在统一上报“实际转发（后折叠）请求”的 provider 实测用量，与 `[acp-usage] input=` 一致。遗留该环境变量 / 配置键的旧值会被忽略，请删除。教训详见 PR #691 的 “Bug 历史教训” 一节。 |
 | `ACP_PROVIDERS` | 指向外部 `providers.json` 的路径（旧版 / 共享文件）。 |
 | `BILI_REPLAY_RETRY_BASE_MS` | acp-loop 回放重试的基础退避延迟（毫秒）：上游瞬时拒绝后重试（默认 `1500`；设 `0` 关闭延迟）。见 #189。 |
 | `BILI_REPLAY_RETRY_MAX` | acp-loop 回放重试的总次数（默认 `3`；设 `1` 彻底关闭重试 —— 旧版 fail-fast 行为）。见 #189。 |

diff --git a/src/config.ts b/src/config.ts
@@ -316,15 +316,6 @@ export type ProxyOptions = {
     autoUpdate: boolean;
     /** Dist-tag channel the auto-updater follows (default "latest"). */
     updateTag: string;
-    /** #408 host-usage backfill mode. "auto" (default) = the uncompressed-
-     *  baseline backfill is armed for plain proxy clients (the bili-launched
-     *  pi/omp extensions are exempted — their host compaction is cancelled, so
-     *  the baseline drives nothing on the host side). "off" = never backfill —
-     *  the usage reported to the host is the actually-forwarded (folded)
-     *  request, matching [acp-usage] input= (#648: plain anthropic proxy
-     *  clients like ZCode otherwise show a cumulative, drifting baseline that
-     *  overstates real context pressure). */
-    hostUsageCredit: "auto" | "off";
     logFile?: string;
     /** MITM transparent-proxy mode. When enabled, an HTTP CONNECT handler is
      *  attached so clients that only know how to set HTTP_PROXY (ZCode with a
@@ -462,7 +453,6 @@ export function loadOptions(env: NodeJS.ProcessEnv = process.env): ProxyOptions
         passthrough: passthrough.enabled,
         passthroughSource: passthrough.source,
         autoUpdate: (env.ACP_AUTO_UPDATE ?? (fileConfig.autoUpdate === false ? "0" : "1")) !== "0",
-        hostUsageCredit: parseHostUsageCredit(env.BILI_HOST_USAGE_CREDIT ?? fileConfig.hostUsageCredit),
         updateTag: (env.ACP_UPDATE_TAG ?? fileConfig.updateTag ?? "latest").trim() || "latest",
         logFile: env.ACP_LOG_FILE !== undefined ? (env.ACP_LOG_FILE || undefined) : fileConfig.logFile,
         mitm: {
@@ -497,7 +487,6 @@ type FileConfig = {
     autoUpdate?: boolean;
     /** Dist-tag channel the auto-updater follows (default "latest"). */
     updateTag?: string;
-    hostUsageCredit?: "auto" | "off";
     upstreamProxy?: string;
     upstreamProxyMode?: string;
     logFile?: string;
@@ -609,10 +598,6 @@ export function parseUpstreamProxyMode(value: string | undefined): UpstreamProxy
     return value === "manual" || value === "auto" ? value : "direct";
 }
 
-export function parseHostUsageCredit(value: string | undefined): "auto" | "off" {
-    return value === "off" ? "off" : "auto";
-}
-
 export function parseCompressSettings(v: unknown): (CompressSettings & { injectTool?: boolean; injectNudge?: boolean }) | undefined {
     if (!v || typeof v !== "object" || Array.isArray(v)) return undefined;
     const obj = v as Record<string, unknown>;

diff --git a/src/exit-matrix.ts b/src/exit-matrix.ts
@@ -1,5 +1,4 @@
 import { emitStreamError, emitPreflightError } from "./stream-error.js";
-import { backfillHostUsage } from "./util.js";
 import { pipePluginChatWithStrip, pipePluginResponsesWithStrip, pipePluginJson } from "./plugin.js";
 import { startServer } from "./server.js";
 
@@ -66,7 +65,7 @@ export const ERROR_DELIVERY: Record<WireExitId, ExitCell> = {
     "plugin-json": {
         implementer: [pipePluginJson],
         contract: "upstream non-2xx/fetch failure → `{error: formatUpstreamError}` JSON; client abort mid-body → clean end, timer cleared",
-        coveredBy: ["tests/issue411-abort-usage.test.ts", "tests/host-usage-backfill.test.ts"],
+        coveredBy: ["tests/issue411-abort-usage.test.ts", "tests/host-usage-postfold.test.ts"],
     },
 };
 
@@ -108,48 +107,48 @@ export const ABORT_PROPAGATION: Record<WireExitId, ExitCell> = {
     },
 };
 
-export const HOST_USAGE_BACKFILL: Record<WireExitId, ExitCell> = {
+export const HOST_USAGE_PASSTHROUGH: Record<WireExitId, ExitCell> = {
     "proxy-openai-sse": {
-        implementer: [backfillHostUsage],
-        contract: "usage frame from the upstream terminal event is credited to the session (input/cached/output), fallback samples on truncation",
-        coveredBy: ["tests/host-usage-backfill.test.ts"],
+        implementer: [startServer],
+        contract: "provider-measured (post-fold) usage credited to the internal ledger and forwarded to the host verbatim — no baseline backfill (#660)",
+        coveredBy: ["tests/host-usage-postfold.test.ts"],
     },
     "proxy-anthropic-sse": {
-        implementer: [backfillHostUsage],
-        contract: "message_start/message_delta usage frames credited",
-        coveredBy: ["tests/host-usage-backfill.test.ts"],
+        implementer: [startServer],
+        contract: "message_start/message_delta usage frames credited, forwarded verbatim",
+        coveredBy: ["tests/host-usage-postfold.test.ts"],
     },
     "proxy-responses-sse": {
-        implementer: [backfillHostUsage],
-        contract: "response.completed usage frame credited (issue #589 frame shape)",
-        coveredBy: ["tests/issue589-usage-frame.test.ts", "tests/host-usage-backfill.test.ts"],
+        implementer: [startServer],
+        contract: "response.completed usage frame credited (issue #589 frame shape), forwarded verbatim",
+        coveredBy: ["tests/issue589-usage-frame.test.ts", "tests/host-usage-postfold.test.ts"],
     },
     "proxy-json": {
-        implementer: [backfillHostUsage],
-        contract: "non-stream usage object credited; no session → skipped (title-gen must not clobber lastInputTokens)",
-        coveredBy: ["tests/host-usage-backfill.test.ts"],
+        implementer: [startServer],
+        contract: "non-stream usage object credited; no session → skipped (title-gen must not clobber lastInputTokens); forwarded verbatim",
+        coveredBy: ["tests/host-usage-postfold.test.ts"],
     },
     "plugin-chat-sse": {
-        implementer: [pipePluginChatWithStrip, backfillHostUsage],
-        contract: "sniffed usage credited unless the call is session-less (#460 title-gen skip)",
-        coveredBy: ["tests/host-usage-backfill.test.ts", "tests/issue411-abort-usage.test.ts"],
+        implementer: [pipePluginChatWithStrip],
+        contract: "sniffed usage credited unless the call is session-less (#460 title-gen skip); stream bytes untouched",
+        coveredBy: ["tests/host-usage-postfold.test.ts", "tests/issue411-abort-usage.test.ts"],
     },
     "plugin-responses-sse": {
-        implementer: [pipePluginResponsesWithStrip, backfillHostUsage],
+        implementer: [pipePluginResponsesWithStrip],
         contract: "sniffed usage credited; verbatim variant skips accounting by design",
-        coveredBy: ["tests/host-usage-backfill.test.ts"],
+        coveredBy: ["tests/host-usage-postfold.test.ts"],
     },
     "plugin-json": {
-        implementer: [pipePluginJson, backfillHostUsage],
-        contract: "JSON usage object credited",
-        coveredBy: ["tests/host-usage-backfill.test.ts"],
+        implementer: [pipePluginJson],
+        contract: "JSON usage object credited; response body forwarded verbatim",
+        coveredBy: ["tests/host-usage-postfold.test.ts"],
     },
 };
 
 export const EXIT_CONCERNS = {
     errorDelivery: ERROR_DELIVERY,
     abortPropagation: ABORT_PROPAGATION,
-    hostUsageBackfill: HOST_USAGE_BACKFILL,
+    hostUsagePassthrough: HOST_USAGE_PASSTHROUGH,
 } as const;
 
 export type ExitConcernId = keyof typeof EXIT_CONCERNS;
diff --git a/src/loop/adapter-anthropic.ts b/src/loop/adapter-anthropic.ts
@@ -118,7 +118,7 @@ function buildTextDeltaEvent(index: number, text: string): Buffer {
     );
 }
 
-export function createAnthropicAdapter(requestBody: Record<string, unknown>, originalSystem?: AnthropicRequestBody["system"], hostCredit = 0): CompressLoopAdapter {
+export function createAnthropicAdapter(requestBody: Record<string, unknown>, originalSystem?: AnthropicRequestBody["system"]): CompressLoopAdapter {
     const model = (requestBody.model as string) ?? undefined;
     let messageId: string | undefined;
     let clientIndex = 0;
@@ -248,26 +248,10 @@ export function createAnthropicAdapter(requestBody: Record<string, unknown>, ori
                     if (typeof u.input_tokens === "number") roundInput = u.input_tokens;
                     if (typeof u.cache_read_input_tokens === "number") roundCached = u.cache_read_input_tokens;
                     if (round === 1) {
-                        // #408: this raw message_start (post-fold input_tokens)
-                        // reaches the host verbatim — add the prepare-time
-                        // credit back so the host anchors on the uncompressed
-                        // baseline.
-                        let chunk = rawBuf;
-                        if (hostCredit > 0 && typeof u.input_tokens === "number") {
-                            const patched = structuredClone(data);
-                            const pmsg = patched["message"] as Record<string, unknown> | undefined;
-                            const pu = (pmsg?.["usage"] ?? {}) as Record<string, unknown>;
-                            if (typeof pu.input_tokens === "number") {
-                                pu.input_tokens += hostCredit;
-                                const out = eventStr
-                                    .split("\n")
-                                    .map((l) => (l.startsWith("data:") ? `data: ${JSON.stringify(patched)}` : l))
-                                    .join("\n");
-                                chunk = Buffer.from(out + "\n\n", "utf8");
-                            }
-                        }
+                        // The raw message_start (with the provider's measured
+                        // usage) reaches the host verbatim — no rewriting.
                         messageStartForwarded = true;
-                        yield { kind: "meta", chunk, firstRoundOnly: true } as ParsedStreamEvent;
+                        yield { kind: "meta", chunk: rawBuf, firstRoundOnly: true } as ParsedStreamEvent;
                     }
                 } else if (type === "ping") {
                     yield { kind: "meta", chunk: rawBuf } as ParsedStreamEvent;

diff --git a/src/loop/adapter-openai.ts b/src/loop/adapter-openai.ts
@@ -116,28 +116,7 @@ function stripFinishReasonChunk(buf: Buffer): Buffer {
     }
 }
 
-function patchUsageChunk(eventStr: string, parsed: Record<string, unknown>, u: Record<string, unknown>, hostCredit: number): Buffer {
-    const pu = typeof u.prompt_tokens === "number" ? u.prompt_tokens : undefined;
-    const tu = typeof u.total_tokens === "number" ? u.total_tokens : undefined;
-    if (hostCredit > 0 && (pu !== undefined || tu !== undefined)) {
-        const patched = {
-            ...parsed,
-            usage: {
-                ...u,
-                ...(pu !== undefined ? { prompt_tokens: pu + hostCredit } : {}),
-                ...(tu !== undefined ? { total_tokens: tu + hostCredit } : {}),
-            },
-        };
-        const out = eventStr
-            .split("\n")
-            .map((l) => (l.startsWith("data:") ? `data: ${JSON.stringify(patched)}` : l))
-            .join("\n");
-        return Buffer.from(out + "\n\n", "utf8");
-    }
-    return Buffer.from(eventStr + "\n\n", "utf8");
-}
-
-export function createOpenaiAdapter(requestBody: Record<string, unknown>, clientSystem?: string, hostCredit = 0, absorbName?: string): CompressLoopAdapter {
+export function createOpenaiAdapter(requestBody: Record<string, unknown>, clientSystem?: string, absorbName?: string): CompressLoopAdapter {
     const model = (requestBody.model as string) ?? "unknown";
     let responseId = `chatcmpl-proxy-${Date.now()}`;
     let toolIndex = 0;
@@ -352,10 +331,10 @@ export function createOpenaiAdapter(requestBody: Record<string, unknown>, client
                         } as ParsedStreamEvent;
                         // #589: include_usage clients (dsh, OpenAI SDK) read usage
                         // from this trailing empty-choices frame; raw tool-call rounds
-                        // must forward it (with the prepare-time credit), not swallow
-                        // it into the internal ledger.
+                        // must forward it verbatim, not swallow it into the internal
+                        // ledger.
                         if (sawRealToolCall) {
-                            yield { kind: "meta", chunk: patchUsageChunk(eventStr, parsed, u, hostCredit) } as ParsedStreamEvent;
+                            yield { kind: "meta", chunk: rawBuf } as ParsedStreamEvent;
                         }
                     }
                     continue;
@@ -376,11 +355,9 @@ export function createOpenaiAdapter(requestBody: Record<string, unknown>, client
                         cachedTokens: typeof pd?.cached_tokens === "number" ? pd.cached_tokens : undefined,
                     } as ParsedStreamEvent;
                     if (sawRealToolCall) {
-                        // #408: this raw finish chunk (with the provider's
-                        // post-fold usage) reaches the host verbatim — add the
-                        // prepare-time credit back so the host anchors on the
-                        // uncompressed baseline.
-                        const chunk = patchUsageChunk(eventStr, parsed, u ?? {}, hostCredit);
+                        // The raw finish chunk (provider-measured usage) reaches
+                        // the host verbatim — no rewriting.
+                        const chunk = rawBuf;
                         // This verbatim chunk IS the round's authoritative completion
                         // (suppressCompletion); write it once and never fall through
                         // to the text/reasoning branches (which would re-emit the same

diff --git a/src/loop/core.ts b/src/loop/core.ts
@@ -177,9 +177,6 @@ function recordUsage(
     // re-sends the unfolded history, so its usage report over-reports the
     // context the NEXT request will actually carry (see stream.ts applyRanges).
     ctx.session.stats.lastInputTokens = Math.max(0, total - (ctx.session.stats.compressCreditTokens ?? 0));
-    // #408: remember the input-side total reported to the host AFTER the
-    // prepare-time fold backfill (uncompressed baseline), for the /acp panel.
-    ctx.session.hostContextTokens = total + (ctx.session.hostCreditTokens ?? 0);
     if (typeof cached === "number") {
         ctx.session.stats.cachedTokens += cached;
         ctx.session.stats.cacheSamples += 1;
@@ -362,16 +359,6 @@ export async function* runCompressLoop(
             ) {
                 recordUsage(ctx, usage, round);
             }
-            // #408: the provider measured the FOLDED (post-compress) view; add
-            // the prepare-time credit back so the completion event the host
-            // anchors on reports the uncompressed baseline. recordUsage above
-            // already ran on the un-backfilled numbers (internal ledger stays
-            // post-fold).
-            const hostCredit = ctx.session.hostCreditTokens ?? 0;
-            if (hostCredit > 0 && typeof usage.inputTokens === "number") {
-                usage.inputTokens += hostCredit;
-            }
-
             let resolvedText = assistantText;
             let allCalls = calls;
             if (ctx.textProtocol && assistantText.length > 0 && adapter.extractTextTriggers) {

diff --git a/src/loop/index.ts b/src/loop/index.ts
@@ -25,11 +25,10 @@ export function pickAdapter(
     responsesProjection?: ResponsesProjection,
     anthropicSystem?: AnthropicRequestBody["system"],
     openaiSystem?: string,
-    hostCredit = 0,
     absorbName?: string,
 ): CompressLoopAdapter {
     if (protocol === "responses") return createResponsesAdapter(textProtocol, responsesProjection, absorbName);
-    if (protocol === "openai") return createOpenaiAdapter(requestBody, openaiSystem, hostCredit, absorbName);
-    if (protocol === "anthropic") return createAnthropicAdapter(requestBody, anthropicSystem, hostCredit);
+    if (protocol === "openai") return createOpenaiAdapter(requestBody, openaiSystem, absorbName);
+    if (protocol === "anthropic") return createAnthropicAdapter(requestBody, anthropicSystem);
     throw new Error(`[acp-loop] unknown protocol: ${protocol}`);
 }