ContextProjection

SUPPORT · type · Type contract

One declared projection: a single fragment or a placement expanded into fragments.

Import

TypeScript

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

JavaScript

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

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

Type: ContextProjection<Input, Id, Placement>

Type expression

type ContextProjection<Input, Id extends string = string, Placement extends string = string> = | {
      readonly kind: 'fragment';
      /** Fragment id; must be unique across all projections. */
      readonly id: Id;
      /** Produces the fragment value; must be synchronous. */
      readonly format: (input: Input) => ContextFragment['value'];
    }
  /** Expands to the fragments supplied for this placement; ids use a separate prefix. */
  | { readonly kind: 'contributions'; readonly placement: Placement };

Type parameters

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

Union branch structure

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

Branch 1

Field	Type	Required	Description
kind	"fragment"	Required	Read-only. See the type definition and usage context.
id	Id	Required	Read-only. Fragment id; must be unique across all projections.
format	(input: Input) => ContextFragment["value"]	Required	Read-only. Produces the fragment value; must be synchronous.

Branch 2

Field	Type	Required	Description
kind	"contributions"	Required	Read-only. See the type definition and usage context.
placement	Placement	Required	Read-only. See the type definition and usage context.

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