upstream-tldraw/templates/agent/worker/prompt/buildSystemPrompt.ts

import { buildResponseSchema } from '../../shared/schema/buildResponseSchema'
import type { ModePart } from '../../shared/schema/PromptPartDefinitions'
import { AgentPrompt } from '../../shared/types/AgentPrompt'
import { getSystemPromptFlags } from './getSystemPromptFlags'
import { buildIntroPromptSection } from './sections/intro-section'
import { buildRulesPromptSection } from './sections/rules-section'

/**
 * Build the system prompt for the agent.
 *
 * This is the main instruction set that tells the AI how to behave.
 * The prompt is constructed from modular sections that adapt based on
 * what actions and parts are available.
 *
 * @param prompt - The prompt containing all parts including the mode part.
 * @param opts - Options for building the system prompt.
 * @param opts.withSchema - Whether to include the JSON schema in the system prompt. Defaults to true.
 * @returns The system prompt string.
 */
export function buildSystemPrompt(
	prompt: AgentPrompt,
	opts: { withSchema: boolean } = { withSchema: true }
): string {
	const { withSchema = true } = opts

	const modePart = prompt.mode
	if (!modePart) {
		throw new Error('A mode part is always required.')
	}

	const { actionTypes, partTypes } = modePart
	const flags = getSystemPromptFlags(actionTypes, partTypes)

	const lines = [buildIntroPromptSection(flags), buildRulesPromptSection(flags)]

	if (withSchema) {
		lines.push(buildSchemaPromptSection(modePart))
	}

	const result = normalizeNewlines(lines.join('\n'))

	return result
}

function buildSchemaPromptSection(modePart: ModePart) {
	const schema = buildResponseSchema(modePart.actionTypes, modePart.modeType)

	return `## JSON schema

This is the JSON schema for the events you can return. You must conform to this schema. You must only return things in this format, otherwise your response will error. Output ONLY the JSON itself — do not add any preamble, explanation, or commentary before or after it, and do NOT wrap your response in a markdown code block (e.g. \`\`\`json). Just the raw JSON object.

${JSON.stringify(schema, null, 2)}
`
}

function normalizeNewlines(text: string): string {
	return text.replace(/\n{3,}/g, '\n\n')
}