ContextSelector

SUPPORT · interface · Type contract

Model or local selector that chooses which reductions to apply.

Import

TypeScript

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

JavaScript

/** @typedef {import('@jangts/agent-core/support').ContextSelector} ContextSelector */

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

Definition

interface ContextSelector

Field structure

Field	Type	Required	Description
id	string	Required	See the type definition and usage context.
maxCalls	number | undefined	Optional	Maximum model calls made through callModel, default 1; 0 permits a local selector.
select	(call: ContextSelectionCall, context: ExecutionContext) => Promise<readonly string[]>	Required	Returns selected reduction ids; unknown ids are rejected.

Member index

Member	Purpose
select	Returns selected reduction ids; unknown ids are rejected.

Member details

select

Returns selected reduction ids; unknown ids are rejected.

ContextSelector.select(call: ContextSelectionCall, context: ExecutionContext): Promise<readonly string[]>

Returns selected reduction ids; unknown ids are rejected.

Parameter	Type	Passing	Description
call	ContextSelectionCall	Required	—
context	ExecutionContext	Required	—

Fields of call

Field	Type	Required	Description
stageId	string	Required	Read-only. See the type definition and usage context.
candidates	readonly ContextSelectionCandidate[]	Required	Reducible candidates, already filtered and measured.
fragments	readonly ContextFragment[]	Required	Only reducible fragments; never protected request or system fragments.
currentTokens	number | undefined	Optional	Current input tokens, when a token budget applies.
requiredReductionTokens	number | undefined	Optional	Tokens that must be removed to satisfy the token budget.
currentChars	number	Required	See the type definition and usage context.
requiredReductionChars	number	Required	Characters that must be removed to satisfy the character budget.
remainingCalls	number	Required	Calls the selector may still spend through callModel.
callModel	ContextModelCall	Required	See the type definition and usage context.

Fields of context

Field	Type	Required	Description
logger	SubFlowLog | undefined	Optional	Read-only. Explicit optional recorder for this operation; never inferred from diagnostics.
signal	AbortSignal	Required	Read-only. Non-optional cancellation signal; never undefined once execution has started.
diagnostics	DiagnosticContext | undefined	Optional	Read-only. Diagnostic scope of the enclosing call, when recording is enabled.

Returns: Promise<readonly string[]>.

Awaited value: readonly string[].

Examples

• Compressors and selectors: recommended implementations and custom algorithms: Bind prompts, output parsing, and algorithms as handlers; model I/O goes through callModel of the same request.

Bind a text compression handler

Beginner · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
const compressor = Support.createContextCompressor({
  id: 'history-summary', instruction: '保留事实、时间和未完成事项，精简重复表达。',
  transport: 'core:plain-text', maxOutputTokens: 500,
  parse(value: unknown) { if (typeof value !== 'string' || !value.trim()) throw new TypeError('需要非空摘要'); return value; },
});
console.log(compressor.id);

JavaScript

import { Support } from '@jangts/agent-core';
const compressor = Support.createContextCompressor({
    id: 'history-summary', instruction: '保留事实、时间和未完成事项，精简重复表达。',
    transport: 'core:plain-text', maxOutputTokens: 500,
    parse(value) { if (typeof value !== 'string' || !value.trim())
        throw new TypeError('需要非空摘要'); return value; },
});
console.log(compressor.id);

A selector explicitly controls the visible excerpt range

Configuration · Node.js

selector-json must be registered by the App and return value={stepIds:string[]}; an ordinary text transport must not be treated as already parsed JSON. This example only shows handler assembly and sends no request.

TypeScript

import { Support } from '@jangts/agent-core';
const selector = Support.createContextSelector({ id: 'select-reduction',
  transport: 'selector-json', maxOutputTokens: 200, maxExcerptChars: 1000,
});
console.log(selector.id);

JavaScript

import { Support } from '@jangts/agent-core';
const selector = Support.createContextSelector({ id: 'select-reduction',
    transport: 'selector-json', maxOutputTokens: 200, maxExcerptChars: 1000,
});
console.log(selector.id);

Related policy source

• Default selection instruction and excerpt range
• Compression request and the real callModel contract

Related definitions

• ContextSelectionCall
• ExecutionContext