createContextStrategy

SUPPORT · function · Runtime value

Build a reduction policy from one or more history declarations.

recent keeps a window of recent groups; continuity summarizes older groups while preserving the most recent originals. Neither preset claims semantic quality, only bounded input size.

Import

TypeScript

import { createContextStrategy } from '@jangts/agent-core/support';

JavaScript

import { createContextStrategy } from '@jangts/agent-core/support';

Other public entry points:@jangts/agent-core/support, @jangts/agent-core/support/context.

Definition

Call

createContextStrategy(options: ContextStrategyOptions | readonly ContextStrategyOptions[], settings?: ContextStrategySettings): ContextStrategy

Build a reduction policy from one or more history declarations.

recent keeps a window of recent groups; continuity summarizes older groups while preserving the most recent originals. Neither preset claims semantic quality, only bounded input size.

Parameter	Type	Passing	Description
options	ContextStrategyOptions | readonly ContextStrategyOptions[]	Required	—
settings	ContextStrategySettings	Optional	—

Fields of settings

Field	Type	Required	Description
selection	ContextSelection | undefined	Optional	See the type definition and usage context.
triggerChars	number | undefined	Optional	See the type definition and usage context.
targetInputChars	number | undefined	Optional	See the type definition and usage context.
targetInputTokens	number | undefined	Optional	See the type definition and usage context.
triggerTokens	number | undefined	Optional	See the type definition and usage context.
steps	readonly ContextReduction[] | undefined	Optional	Read-only. See the type definition and usage context.
compressors	readonly ContextCompressor[] | undefined	Optional	Read-only. See the type definition and usage context.
selectors	readonly ContextSelector[] | undefined	Optional	Read-only. See the type definition and usage context.

Optional shapes of Parameter options: choose one shape; required fields for each branch are listed separately.

Branch 1

Field	Type	Required	Description
fragment	Pick<ContextFragment, "id" | "maxChars">	Required	Read-only. Reuse the registered fragment identity and its existing hard size allowance.
field	string	Required	Read-only. See the type definition and usage context.
preset	"compact" | "balanced" | "extended" | undefined	Optional	Read-only. See the type definition and usage context.
targetChars	number | undefined	Optional	Read-only. See the type definition and usage context.
keepGroups	number | undefined	Optional	Read-only. See the type definition and usage context.
grouping	ContextHistoryGrouping | undefined	Optional	Read-only. See the type definition and usage context.
selection	ContextSelection | undefined	Optional	See the type definition and usage context.
triggerChars	number | undefined	Optional	See the type definition and usage context.
targetInputChars	number | undefined	Optional	See the type definition and usage context.
targetInputTokens	number | undefined	Optional	See the type definition and usage context.
triggerTokens	number | undefined	Optional	See the type definition and usage context.
steps	readonly ContextReduction[] | undefined	Optional	Read-only. See the type definition and usage context.
compressors	readonly ContextCompressor[] | undefined	Optional	Read-only. See the type definition and usage context.
selectors	readonly ContextSelector[] | undefined	Optional	Read-only. See the type definition and usage context.
kind	"recent"	Required	Read-only. See the type definition and usage context.
compressor	undefined	Optional	Read-only. See the type definition and usage context.

Branch 2

Field	Type	Required	Description
fragment	Pick<ContextFragment, "id" | "maxChars">	Required	Read-only. Reuse the registered fragment identity and its existing hard size allowance.
field	string	Required	Read-only. See the type definition and usage context.
preset	"compact" | "balanced" | "extended" | undefined	Optional	Read-only. See the type definition and usage context.
targetChars	number | undefined	Optional	Read-only. See the type definition and usage context.
keepGroups	number | undefined	Optional	Read-only. See the type definition and usage context.
grouping	ContextHistoryGrouping | undefined	Optional	Read-only. See the type definition and usage context.
selection	ContextSelection | undefined	Optional	See the type definition and usage context.
triggerChars	number | undefined	Optional	See the type definition and usage context.
targetInputChars	number | undefined	Optional	See the type definition and usage context.
targetInputTokens	number | undefined	Optional	See the type definition and usage context.
triggerTokens	number | undefined	Optional	See the type definition and usage context.
steps	readonly ContextReduction[] | undefined	Optional	Read-only. See the type definition and usage context.
compressors	readonly ContextCompressor[] | undefined	Optional	Read-only. See the type definition and usage context.
selectors	readonly ContextSelector[] | undefined	Optional	Read-only. See the type definition and usage context.
kind	"continuity"	Required	Read-only. See the type definition and usage context.
compressor	ContextCompressor	Required	Read-only. See the type definition and usage context.

Branch 3

Field	Type	Required	Description
selection	ContextSelection | undefined	Optional	See the type definition and usage context.
triggerChars	number | undefined	Optional	See the type definition and usage context.
targetInputChars	number | undefined	Optional	See the type definition and usage context.
targetInputTokens	number | undefined	Optional	See the type definition and usage context.
triggerTokens	number | undefined	Optional	See the type definition and usage context.
steps	readonly ContextReduction[]	Required	Read-only. See the type definition and usage context.
compressors	readonly ContextCompressor[] | undefined	Optional	Read-only. See the type definition and usage context.
selectors	readonly ContextSelector[] | undefined	Optional	Read-only. See the type definition and usage context.
fragment	Pick<ContextFragment, "id" | "maxChars"> | undefined	Optional	Read-only. Reuse the registered fragment identity and its existing hard size allowance.
field	string | undefined	Optional	Read-only. See the type definition and usage context.
preset	"compact" | "balanced" | "extended" | undefined	Optional	Read-only. See the type definition and usage context.
targetChars	number | undefined	Optional	Read-only. See the type definition and usage context.
keepGroups	number | undefined	Optional	Read-only. See the type definition and usage context.
grouping	ContextHistoryGrouping | undefined	Optional	Read-only. See the type definition and usage context.
kind	"recent" | "continuity" | undefined	Optional	Read-only. See the type definition and usage context.
compressor	ContextCompressor | undefined	Optional	Read-only. See the type definition and usage context.

Branch 4

readonly ContextStrategyOptions[]

Returns: ContextStrategy.

Return value structure

Field	Type	Required	Description
policy	ContextPolicy	Required	Read-only. Reduction policy with the generated or explicit steps and selection.
compressors	readonly ContextCompressor[]	Required	Read-only. Compressors referenced by generated compression steps, deduplicated by identity.
selectors	readonly ContextSelector[]	Required	Read-only. Selectors available to model-driven selection.

Examples

• Generate processing strategies from history semantics: Reuse fragment identity and hard budgets to generate complete steps and references for recent or continuity.

Reuse an existing fragment to generate a recent-history strategy

Beginner · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const fragment = { id: 'history', maxChars: 4000 };
const strategy = Support.createContextStrategy({ kind: 'recent', fragment, field: 'messages' });
console.log(strategy.policy, strategy.compressors);

JavaScript

import { Support } from '@jangts/agent-core';
const fragment = { id: 'history', maxChars: 4000 };
const strategy = Support.createContextStrategy({ kind: 'recent', fragment, field: 'messages' });
console.log(strategy.policy, strategy.compressors);

Add kept groups and target size to the same configuration

Configuration · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const fragment = { id: 'history', maxChars: 4000 };
const strategy = Support.createContextStrategy({ kind: 'recent', fragment, field: 'messages',
  keepGroups: 3, targetChars: 2500, grouping: { kind: 'user-turn' },
});
console.log(strategy.policy);

JavaScript

import { Support } from '@jangts/agent-core';
const fragment = { id: 'history', maxChars: 4000 };
const strategy = Support.createContextStrategy({ kind: 'recent', fragment, field: 'messages',
    keepGroups: 3, targetChars: 2500, grouping: { kind: 'user-turn' },
});
console.log(strategy.policy);

Supply a compression algorithm explicitly when old topics must be carried forward

Extension · Node.js

This example only assembles the strategy. The policy/compressors/selectors are used as configuration for existing context nodes; no new request is sent and no extra budget is created here.

TypeScript

import { Support } from '@jangts/agent-core';
const compressor = Support.createContextCompressor({ id: 'history-summary',
  instruction: '按资料原意概括旧历史，保留事实、时间和未完成事项。',
  transport: 'core:plain-text', maxOutputTokens: 500,
  parse(value: unknown) { if (typeof value !== 'string' || !value.trim()) throw new TypeError('需要摘要'); return { messages: [{ role: 'user', content: value }] }; },
});
const strategy = Support.createContextStrategy({ kind: 'continuity',
  fragment: { id: 'history', maxChars: 4000 }, field: 'messages', compressor,
  targetChars: 2500, keepGroups: 2,
});
console.log(strategy.policy, strategy.compressors.map(item => item.id));

JavaScript

import { Support } from '@jangts/agent-core';
const compressor = Support.createContextCompressor({ id: 'history-summary',
    instruction: '按资料原意概括旧历史，保留事实、时间和未完成事项。',
    transport: 'core:plain-text', maxOutputTokens: 500,
    parse(value) { if (typeof value !== 'string' || !value.trim())
        throw new TypeError('需要摘要'); return { messages: [{ role: 'user', content: value }] }; },
});
const strategy = Support.createContextStrategy({ kind: 'continuity',
    fragment: { id: 'history', maxChars: 4000 }, field: 'messages', compressor,
    targetChars: 2500, keepGroups: 2,
});
console.log(strategy.policy, strategy.compressors.map(item => item.id));

Related policy source

• Scenario catalog, generated steps, and precise overrides

Related definitions

• ContextStrategy
• ContextStrategyOptions
• ContextStrategySettings