# 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#L40) ### ctx.compact.compactIfNeeded(agent, trigger, signal) ```ts website-api /** * 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 ``` 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. - `agent` — agent context owning the session surface and routing options. - `trigger` — normal pressure or provider-confirmed context overflow. - `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#L57) ### ctx.compact.compactRegion(start, end, agent, signal?) ```ts website-api /** * 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 {@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 ``` 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#L80)