Rebuild the pipeline on LangChain

src/pipeline.js

// The whole generator, rebuilt on LangChain chat models:
//
//   (optional) research → outline → write the deck → compile → repair what's broken
//
// It replaces generate.js. The steps are the same; what changed is that each
// step receives a `model`, so we can swap in a different model, or a fake one in tests.

import { HumanMessage, SystemMessage } from "@langchain/core/messages";
import { contentText, createModel } from "./llm.js";
import { generateOutline } from "./outline.js";
import { researchTopic } from "./research.js";
import { buildSystemPrompt, extractTag } from "./prompt.js";
import { LIBRARY } from "./library.js";
import { compileDeck } from "./compile.js";

const MAX_REPAIR_ROUNDS = 2;

/** Outline → SlideML, following the component library. */
export async function writeDeck(model, outline) {
  const reply = await model.invoke([
    new SystemMessage(buildSystemPrompt(LIBRARY)),
    new HumanMessage(`Write the deck for this outline:\n${JSON.stringify(outline, null, 2)}`),
  ]);
  const xml = extractTag(contentText(reply), "deck");
  if (!xml) throw new Error("The model didn't reply with a <deck> element.");
  return xml;
}

/** Send the deck back with the compiler's problems and ask for a corrected deck. */
export async function repairDeck(model, xml, problems) {
  const list = problems.map((problem) => `- Slide ${problem.slide}: ${problem.message}`).join("\n");
  const reply = await model.invoke([
    new SystemMessage(buildSystemPrompt(LIBRARY)),
    new HumanMessage(`This deck has problems:\n${list}\n\nFix them and reply with the whole corrected <deck>.\n\n${xml}`),
  ]);
  return extractTag(contentText(reply), "deck");
}

/**
 * options:
 *   model       a LangChain chat model (default: createModel())
 *   research    true to search the web first
 *   slideCount  how many slides to plan (default 6)
 *   theme       "light" or "dark"
 *   compile     the compiler to use (tests pass a fake one)
 */
export async function generateDeck(topic, options = {}) {
  const { model = createModel(), research = false, slideCount = 6, theme, compile = compileDeck } = options;

  const findings = research ? await researchTopic(model, topic) : { notes: "", sources: [] };
  const outline = await generateOutline(model, topic, { slideCount, research: findings.notes });
  let xml = await writeDeck(model, outline);
  let result = compile(xml, theme);
  let repairs = 0;

  while (result.problems.length > 0 && repairs < MAX_REPAIR_ROUNDS) {
    repairs += 1;
    const fixed = await repairDeck(model, xml, result.problems);
    if (!fixed) break;
    const next = compile(fixed, theme);
    if (next.problems.length >= result.problems.length) break;
    xml = fixed;
    result = next;
  }

  return { outline, xml, slides: result.slides, problems: result.problems, repairs, sources: findings.sources };
}