ContextAssemblyOptions

SUPPORT · interface · Type contract

Assembly options for placement-based projections.

Import

TypeScript

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

JavaScript

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

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 ContextAssemblyOptions<Input, Id, Placement>

Extends or implements: ContextBuilderOptions<Input>.

Type parameters

Type parameter	Constraint	Default type
Input	—	—
Id	string	—
Placement	string	—

Field structure

Field	Type	Required	Description
fragment	(id: Id, value: ContextFragment["value"]) => ContextFragment	Required	Read-only. Builds a fragment for a single-fragment projection.
contributions	Readonly<Record<Placement, (input: Input) => readonly ContextFragment[]>> | undefined	Optional	Read-only. Contribution handlers keyed by placement; each expands to zero or more fragments.
maxInputChars	number | ((input: Input) => number) | undefined	Optional	Read-only. Character budget, constant or derived from the request; at least one of these is required.
transform	((fragment: ContextFragment, input: Input) => ContextFragment) | undefined	Optional	Read-only. Applied to every produced fragment before assembly; must be synchronous.

Member index

Member	Purpose
fragment	Builds a fragment for a single-fragment projection.

Member details

fragment

Builds a fragment for a single-fragment projection.

ContextAssemblyOptions.fragment(id: Id, value: ContextFragment["value"]): ContextFragment

Parameter	Type	Passing	Description
id	Id	Required	—
value	string | Record<string, unknown>	Required	—

Returns: ContextFragment.

Return value structure

Field	Type	Required	Description
id	string	Required	Unique, stable id matching ^[a-z][a-zA-Z0-9:._-]*$; duplicates are rejected.
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.
role	"system" | "user"	Required	Message slot the fragment occupies when assembled.
value	string | Record<string, unknown>	Required	Rendered content. A system message accepts a string only, never a record.

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

• ContextBuilderOptions
• ContextFragment