deepseek-harness/website/zh-CN/api/harness/compact.md

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# ctx.compact

`CompactService` (abstract seam) — provided by `@deepseek-ai/dsh-compact`.

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. Load one implementation per context as `ctx.compact`.

[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/compact/compact/src/index.ts#L38)

### ctx.compact.compactIfNeeded(agent, fullSystemPrompt, sessionPrefix, signal)

```ts website-api
abstract compactIfNeeded( agent: CompactAgentContext, fullSystemPrompt: string, sessionPrefix: readonly Message[], signal: AbortSignal, ): Promise<CompactionResult | null>
```

Check token pressure and compact if the conversation is too large. Estimate the next request, including its session prefix, derived history, and system prompt. Above threshold, compact a head-anchored range ending at a balanced tool boundary and reconsolidate any prior automatic checkpoint. Return `null` when no compaction is needed or an open tail leaves no safe cutoff. A single oversized retained unit or prefix cannot be repaired here.

- `agent` — agent context owning the session surface and model options.
- `fullSystemPrompt` — assembled system prompt, counted toward the estimate.
- `sessionPrefix` — the instance's composed session prefix, counted toward the estimate.
- `signal` — cancellation signal; model-backed implementations must forward it.

**Returns** the compaction result, or `null` if no compaction was needed.

[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/compact/compact/src/index.ts#L58)

### ctx.compact.compactRegion(start, end, agent, signal?)

```ts website-api
abstract compactRegion( start: number, end: number, agent: CompactAgentContext, signal?: AbortSignal, ): Promise<CompactionResult>
```

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`. Use toolPairingBalancedBefore and toolPairingBalancedAfter for the edge checks.

- `start` — first surface seq, inclusive.
- `end` — last surface seq, inclusive.
- `agent` — context whose session is mutated and whose routing options guide summarization.
- `signal` — optional cancellation; model-backed implementations must forward it.

**Returns** the appended event seqs, summary, replaced range, and token accounting.

[Source](https://github.com/deepseek-harness/deepseek-harness/blob/master/packages/compact/compact/src/index.ts#L82)