ContextFragmentConfig

SUPPORT · interface · Type contract

Self-describing fragment declaration: metadata plus a formatter.

Import

TypeScript

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

JavaScript

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

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

Definition

interface ContextFragmentConfig<Input>

Extends or implements: Omit<ContextFragment, 'value'>.

Type parameters

Type parameter	Constraint	Default type
Input	—	—

Field structure

Field	Type	Required	Description
description	string | undefined	Optional	Read-only. Documentation only; not sent to the model.
format	(input: Input) => ContextFragment["value"]	Required	Read-only. Produces the value; must be synchronous.
id	string	Required	Unique, stable id matching ^[a-z][a-zA-Z0-9:._-]*$; duplicates are rejected.
role	"system" | "user"	Required	Message slot the fragment occupies when assembled.
sourceId	string	Required	Owning source (module or registration) used to explain where the content came from.
trust	ContextTrust	Required	Producer trust level. user and tool content cannot become a system message.
lifetime	ContextLifetime	Required	Declared validity window of this content.
maxChars	number	Required	Hard upper bound in JSON characters; must be a positive safe integer.

Member index

Member	Purpose
format	Produces the value; must be synchronous.

Member details

format

Produces the value; must be synchronous.

ContextFragmentConfig.format(input: Input): ContextFragment["value"]

Parameter	Type	Passing	Description
input	Input	Required	—

Returns: string \| Record<string, unknown>.

Examples

• Context assembly: configure stable metadata once: Support binds fragment metadata, formatting, and order in advance, and requests supply only the changing business input.

Configure once, then supply only question and history

Beginner · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
type Input = { question: string; history: readonly { role: string; content: string }[] };
const builder = Support.defineContextFragments<Input>([
  { id: 'question', sourceId: 'request', trust: 'user', lifetime: 'turn', maxChars: 1000,
    role: 'user', format: input => input.question },
  { id: 'history', sourceId: 'conversation', trust: 'user', lifetime: 'turn', maxChars: 10000,
    role: 'user', format: input => ({ messages: input.history }) },
], { maxInputChars: 1200 });
const context = builder.build({ input: { question: '服务状态？', history: [] } });
console.log(context.messages);

JavaScript

import { Support } from '@jangts/agent-core';
const builder = Support.defineContextFragments([
    { id: 'question', sourceId: 'request', trust: 'user', lifetime: 'turn', maxChars: 1000,
        role: 'user', format: input => input.question },
    { id: 'history', sourceId: 'conversation', trust: 'user', lifetime: 'turn', maxChars: 10000,
        role: 'user', format: input => ({ messages: input.history }) },
], { maxInputChars: 1200 });
const context = builder.build({ input: { question: '服务状态？', history: [] } });
console.log(context.messages);

The same builder produces a plan in advance

Configuration · Node.js

TypeScript

import { Support } from '@jangts/agent-core';
type Input = { question: string; history: readonly { role: string; content: string }[] };
const builder = Support.defineContextFragments<Input>([
  { id: 'question', sourceId: 'request', trust: 'user', lifetime: 'turn', maxChars: 1000,
    role: 'user', format: input => input.question },
  { id: 'history', sourceId: 'conversation', trust: 'user', lifetime: 'turn', maxChars: 10000,
    role: 'user', format: input => ({ messages: input.history }) },
], { maxInputChars: 1200 });
const input = { question: '服务状态？', history: [] };
const plan = builder.plan({ input });
const expanded = builder.fragments(input);
console.log(plan.maxInputChars, expanded.map(fragment => fragment.id));
const largerRequest = builder.build({ input, maxInputChars: 2000 });
console.log(largerRequest.maxInputChars);

JavaScript

import { Support } from '@jangts/agent-core';
const builder = Support.defineContextFragments([
    { id: 'question', sourceId: 'request', trust: 'user', lifetime: 'turn', maxChars: 1000,
        role: 'user', format: input => input.question },
    { id: 'history', sourceId: 'conversation', trust: 'user', lifetime: 'turn', maxChars: 10000,
        role: 'user', format: input => ({ messages: input.history }) },
], { maxInputChars: 1200 });
const input = { question: '服务状态？', history: [] };
const plan = builder.plan({ input });
const expanded = builder.fragments(input);
console.log(plan.maxInputChars, expanded.map(fragment => fragment.id));
const largerRequest = builder.build({ input, maxInputChars: 2000 });
console.log(largerRequest.maxInputChars);

Related policy source

• Assembly order, dependency snapshots, and request budget overrides

Related definitions

• ContextFragment
• ContextLifetime
• ContextTrust