# 压缩（compaction）

[English](compaction.md) | 中文

压缩 seam 是一个[能力 seam](../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md)，与 bash 一样分为 Service Definition（[dsh-compact](../../packages/compact/compact)，`ctx.compact`）、Service provider（例如 [dsh-compact-basic](../../packages/compact/compact-basic) 后端）和面向用户的 Consumer（[dsh-command-compact](../../packages/compact/command-compact)）。压缩是**一项可选能力**，不属于 agent loop（智能体循环）主干，因此其词汇定义在此而非 [core.md](core.md) 中。基于 tokenizer 或模板的后端是实现同一接口的兄弟包。与 bash 不同，该接口必然依赖 `dsh-session` 和 `dsh-llm`：其动词作用于 agent 所有的 `Session`，而其持久摘要事件使用 `ContentBlock` 词汇（见[压缩能力 seam Agent Note](../../.agents/notes/implemented/feature/2026-06-18-compaction-capability-seam.md)）。

源码：[`packages/compact/compact/src/types.ts`](../../packages/compact/compact/src/types.ts)

## `compact/*` 会话事件

压缩通过声明合并为 [`SessionEventMap`](session.md) 扩展三种事件类型。三者都**仅写入日志**——它们记录锁、摘要、选中范围、被遮蔽事件 seq、token 数以及模型调用，绝不进入 surface。这里有意不扩展 `SurfaceEventType`（只有产生消息的事件才到达模型），因此摘要本身承载在另一条带有 `surfaceOp: { op: 'replace', start, end }` 的 `user/message` 上——这是摘要压缩执行的唯一 surface 变更。关于复用 `user/message` 为何是如实建模而非权宜之计，见对应 Agent Note。

| 事件 | 载荷 | 作用 |
|---|---|---|
| `compact/start` | `{ turn }` | 获取日志记录的锁；数字标识打开的自动轮次，`null` 标识独立手动尝试 |
| `compact/summary` | `{ summary, rawOutput?, llmStreamCall?, shadowedRange, shadowedSeqs, shadowedTokenCount, provider, model, maxTokens?, usage? }` | 安全摘要投影、可选的完整 provider 输出与 usage、生成结果时恰好通过此上下文的 `ctx.llm.stream()` 发起一次调用所带的 `llmStreamCall: true` 标记（此时必须提供完整的 `rawOutput`）、被遮蔽的 surface 边界对（`start`/`end` seq——位置跨度，而非数值区间）、按 surface 顺序排列的被遮蔽 seq、估算 token 数，以及摘要调用的 envelope（`provider`、`model`，若有生成上限则还包括该上限）——写入日志后，该一次性请求可由日志 + 代码重建（见可重建性 Agent Note）；未带标记的 `rawOutput` 并不能判定调用路径 |
| `compact/end` | `{ turn, error? }` | 使用相同的数字或 `null` 归属值释放锁（`error` 记录失败尝试） |

锁括住**整个**操作：先追加 `compact/start`，然后执行摘要生成、写入 `compact/summary` 记录与 `user/message` 替换，最后才追加 `compact/end`。最后释放锁意味着操作中途崩溃会表现为可检测的遗留锁（有 `compact/start` 而无匹配的 `compact/end`），而非一个虚假声称压缩已完成的 `compact/end`。

这些标记表示锁的时间点，而不是排他的容器。摘要等待期间，不相关的空闲注入可以出现在独立的手动 start 与 end 之间。手动路径只重新验证所选位置 span，因此替换检查点之后仍保留该注入上下文。活动的未匹配 start 会阻塞所有入口点；较新 `session/end-seed` 之前的未匹配 start 是先前生命周期留下的陈旧证据，会被忽略。

这些变体在 `declare module '@deepseek-ai/dsh-session'` 块内合并，因此——与其他子系统页面上的顶层类型不同——它们不以漂移检查的 ` ```ts type-equiv ` 块粘贴（`verify-type-equiv` 提取器只按名称匹配顶层声明）。上方的载荷表即为目录条目；权威形状请循源码链接查看。

## `CompactionResult`

成功压缩向调用方返回：记账事件 seq、安全摘要投影、被遮蔽的范围与 seq，以及估算 token 数。

```ts type-equiv
/** Result of a successful compaction operation. */
interface CompactionResult {
  /** The seq of the appended `compact/start` event. */
  startSeq: number
  /** The seq of the appended `compact/summary` event. */
  summarySeq: number
  /** The seq of the appended `compact/end` event. */
  endSeq: number
  /** The summary content blocks produced by the backend. */
  summary: ContentBlock[]
  /**
   * The surface-boundary pair that was shadowed: the seqs of the first
   * (`start`) and last (`end`) surface nodes of the replaced range. A
   * surface-POSITION span, not a numeric seq interval — after a prior replace
   * lands a fresh high-seq summary node at an older range's position, `start`
   * can be GREATER than `end`. {@link CompactionResult.shadowedSeqs} is the
   * authoritative set of shadowed nodes, in surface order.
   */
  shadowedRange: { start: number; end: number }
  /** The seqs of all shadowed surface nodes, in surface order. */
  shadowedSeqs: number[]
  /** Estimated token count of the shadowed content. */
  shadowedTokenCount: number
}
```

## 服务

自动调用方会说明策略为何运行；实现可以比普通压力更激进地处理已确认的溢出。

```ts type-equiv
/** Why automatic policy is asking a backend to consider compaction. */
type CompactionTrigger = 'pressure' | 'context-overflow'
```

`CompactService` 暴露 `compactIfNeeded(agent, trigger, signal)` 以执行自动 `pressure` 或 `context-overflow` 策略，暴露 `compactNow(agent, signal)` 以便即使未达到压力也对空闲会话进行一次有效缩减，还针对显式、两端均包含的 surface 范围暴露 `compactRegion(...)`。`compactNow()` 作为轮次之间的 agent maintenance 运行；没有有效范围时返回 `null` 且不写入；在摘要前记录独立的 `turn: null` 标记对，并在后续排队提示词能够从新表层派生前 flush 已闭合尝试。每个后端都使用 `COMPACT_CHECKPOINT_SOURCE` 标记其替换用的 `user/message`；client 与 wire 消费方从无 cordis 的 `@deepseek-ai/dsh-compact/checkpoint` 子路径导入该值和 `isCompactCheckpointSource()`，包根则为 host 消费方重新导出两者。该判定函数使检查点识别不依赖任一特定后端。实现必须把传入的 signal 转发给摘要流程。该 seam 不拥有计价 API：单例 [`ctx.tokenMeter`](token-meter.md) 直接拥有估算与回放，而 `dsh-compact-basic` 拥有保留策略、事件排序、按路由执行的摘要调用及其配置。

预期的手动失败使用 `ManualCompactionErrorCode`：

```ts type-equiv
/** Expected failure classes for an explicit idle-session compaction request. */
type ManualCompactionErrorCode =
  | 'busy'
  | 'cancelled'
  | 'changed'
  | 'summary'
  | 'commit'
  | 'persistence'
```

`changed` 和 `summary` 保持会话表层不变，但仍会闭合失败尝试并将其持久化到日志。`commit` 可能发生在部分变更之后；`persistence` 表示内存中的标记对已闭合，但 flush 失败。取消独立于这些失败，并在完成必要清理后抛出原始 abort 原因。

压力压缩在串行 `agent/pre-step` 中运行，先于请求推导。一旦压力或规范化溢出满足条件，compact-basic 会在选择范围前调用可选的 [`ctx.toolResultPrune`](../../packages/compact/compact-tool-result-prune/README.md)，再通过 `ctx.tokenMeter` 重新测量，并且可以在不生成摘要的情况下推进 surface。失败请求的恢复在失败的步骤关闭后通过 `agent/request-error` 运行；仅当 surface replacement generation 前进时才返回重试动作，即便后续摘要工作在剪枝后抛异常亦如此；取消仍然优先。区域边界保持工具调用/结果配对，但不保持整个轮次，因此一个过大轮次中较早关闭的步骤可以被压缩。`dsh-compact-basic` 拥有阈值、保留尾部策略、溢出上限与失败处理。

该 Service Definition 导出 `toolPairingBalancedBefore(session, seq)` 与 `toolPairingBalancedAfter(session, seq)`，用于这些边缘检查。两者都会验证当前 surface 成员关系，并拒绝缺失的 seq 与遗留结果；其缓存语义由[包约定](../../packages/compact/compact/README.md#tool-pairing-boundaries)规定。

## 工具结果剪枝产出

可选的工具结果剪枝服务会报告每次持久内容替换以及 Unicode code point 的总减少量。其公开结果类型位于 [`compact-tool-result-prune/src/types.ts`](../../packages/compact/compact-tool-result-prune/src/types.ts)。

```ts type-equiv
/** Cited source event and size accounting for one landed surface replacement. */
interface PrunedEntry {
  /** Full-fidelity tool-result event shadowed by the replacement. */
  readonly originalSeq: number
  /** Newly appended pruned tool-result event. */
  readonly replacementSeq: number
  /** Tool call shared by the original and replacement. */
  readonly callId: CallId
  /** Original text size in Unicode code points. */
  readonly charsBefore: number
  /** Replacement text size in Unicode code points. */
  readonly charsAfter: number
}
```

```ts type-equiv
/** Aggregate outcome of one stable-surface pruning pass. */
interface PruneResult {
  /** Replacements in the snapshotted surface order. */
  readonly pruned: readonly PrunedEntry[]
  /** Total Unicode code points removed across replacements. */
  readonly charsRemoved: number
}
```

<!-- BEGIN GENERATED cordis-surface (gen-cordis-catalog.ts) — do not edit between markers -->

<a id="cordis-surface"></a>

## Cordis surface

Generated from source by `scripts/gen-cordis-catalog.ts` (verified fresh by `pnpm run verify-cordis-catalog` in doc-sync; regenerate with `pnpm run gen-cordis-catalog`) — this section is byte-identical in both language sides of the page. Signature blocks use a `ts cordis-catalog` fence and keep the original source JSDoc; dispatch modes are defined in the [primer](../cordis-primer.md#dispatch-modes), and the framework-inherited `ctx` surface lives in [cordis-api/inherited.md](../cordis-api/inherited.md).

<a id="ctxcompact--compactservice-abstract-seam"></a>

### `ctx.compact` — `CompactService` (abstract seam)

Abstract compaction service. Implementations own trigger policy, retention, and summarization, and may consume a separate measurement service. A successful run replaces the selected surface span with one summary node and prevents concurrent compaction of the same session. The replacement user message uses COMPACT_CHECKPOINT_SOURCE so consumers recognize it independently of the backend. Load one implementation per context as `ctx.compact`.

```ts cordis-catalog
/**
 * Consider automatic compaction for one explicit trigger. Pressure policy
 * uses the latest durable routed request, while context-overflow policy may
 * force a useful balanced reduction even below the normal threshold. Return
 * `null` when no safe range can be compacted. A single oversized retained
 * unit or request envelope cannot be repaired through surface compaction.
 *
 * @param agent - agent context owning the session surface and routing options.
 * @param trigger - normal pressure or provider-confirmed context overflow.
 * @param signal - cancellation signal; model-backed implementations must forward it.
 * @returns the compaction result, or `null` if no compaction was needed.
 */
abstract compactIfNeeded( agent: CompactAgentContext, trigger: CompactionTrigger, signal: AbortSignal, ): Promise<CompactionResult | null>

/**
 * Explicitly compact useful history even below automatic pressure thresholds.
 * Implementations synchronously start an idle task before any asynchronous
 * work, select a useful range without writing on a no-op, then
 * append a standalone `compact/start` before summarization. That durable
 * marker is the compaction lock until one `compact/end` attempt. Later waking
 * prompts remain accepted in FIFO order and start only after the optional
 * durability checkpoint and idle-task settlement. Context injected while the
 * summary runs may sit between the marker pair; only the selected span must
 * remain stable.
 *
 * @param agent - idle agent whose durable history should be compacted.
 * @param signal - cancellation scoped to this compaction request.
 * @returns the compaction result, or `null` when no safe useful range exists.
 * @throws {@link ManualCompactionError} for expected busy, agent-cancellation,
 * changed-span, summarization/shrink, commit-stage, or persistence failures;
 * an aborted request preserves its exact abort reason. Failed attempts remain
 * visible in the log.
 */
abstract compactNow( agent: ManualCompactAgentContext, signal: AbortSignal, ): Promise<CompactionResult | null>

/**
 * Forcibly compact a range of surface nodes into a single summary node.
 * `start` and `end` name an inclusive span by surface position, not numeric seq
 * order; replacements can make visible seqs non-monotonic. Both edges must be
 * balanced so assistant tool calls remain paired with their results. A model-
 * backed implementation forwards cancellation and rejects active, missing,
 * reversed, or unbalanced ranges. The target session is `agent.session`.
 * Its replacement user message must use {@link COMPACT_CHECKPOINT_SOURCE}.
 * Use {@link toolPairingBalancedBefore} and {@link toolPairingBalancedAfter}
 * for the edge checks.
 *
 * @param start - first surface seq, inclusive.
 * @param end - last surface seq, inclusive.
 * @param agent - context whose session is mutated and whose routing options guide summarization.
 * @param signal - optional cancellation; model-backed implementations must forward it.
 * @throws when compaction is active or the range is missing, reversed, or unbalanced.
 * @returns the appended event seqs, summary, replaced range, and token accounting.
 */
abstract compactRegion( start: number, end: number, agent: CompactAgentContext, signal?: AbortSignal, ): Promise<CompactionResult>
```

Source: [`packages/compact/compact/src/index.ts:93`](../../packages/compact/compact/src/index.ts)

<a id="ctxtoolresultprune--toolresultpruneservice"></a>

### `ctx.toolResultPrune` — `ToolResultPruneService`

Deterministic head/middle/tail pruning for current tool-result surface nodes.

```ts cordis-catalog
/**
 * Measure text content in Unicode code points; non-text blocks cost zero.
 * @param blocks - tool-result content to measure.
 * @returns total Unicode code points across text blocks.
 */
measureContent(blocks: readonly ContentBlock[]): number

/**
 * Replace an over-budget text middle while retaining rich-block order.
 * Text slicing is by Unicode code point, not UTF-16 code unit, so a retained
 * boundary cannot split a surrogate pair. Grapheme clusters may still split.
 * @param blocks - original tool-result content.
 * @returns pruned content, or `null` when the text is within budget.
 */
pruneContent(blocks: readonly ContentBlock[]): ContentBlock[] | null

/**
 * Prune every over-budget tool result from one stable current-surface snapshot.
 * Each replacement preserves the complete event data except for `content`,
 * cites the shadowed node so replay can recover the replacement input, and is
 * immediately preceded by a `compact/prune` shadow-price event pricing the
 * shadowed node through the injected token meter, so pure consumers can
 * subtract it without per-node state.
 * @param session - session whose current surface is rewritten.
 * @returns landed replacements and aggregate Unicode-code-point savings.
 * @throws when the session rejects a replacement; replacements committed
 * earlier in the pass remain durable.
 */
pruneSession(session: Session): PruneResult
```

Types: [ContentBlock](llm-streaming.md) · [Session](session.md)

Source: [`packages/compact/compact-tool-result-prune/src/index.ts:44`](../../packages/compact/compact-tool-result-prune/src/index.ts)
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