Initial commit: LangChain evolution tutorial deck (132 slides)

- Cover, TOC, 5 dividers, 3 recap slides
- 5 sections (chains, langgraph, deepagents, openswe, ecosystem)
- design-system.js with theme tokens + 9 helper functions
- research/: timeline + sources + per-tech notes
- final-compile.js + merge.js for rebuild pipeline
- output/: langchain-evolution.pptx (2.3 MB) + langchain-evolution.pdf (1.1 MB) + 7 sample previews

slides/section1-chains/slide-13.js

@@ -0,0 +1,56 @@
+// Slide 13: LCEL -- the pipe operator and the Runnable protocol
+// Code slide: every component is a Runnable, | composes them.
+
+const ds = require('./design-system');
+
+function createSlide(pres, theme) {
+  const slide = pres.addSlide();
+  ds.helpers.slideBase(slide, pres, theme);
+
+  ds.helpers.addHeader(slide, pres, theme, {
+    eyebrow: 'STAGE 1: CHAINS',
+    section: 'LCEL',
+    title: '| -- декларативная композиция',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/lcel_intro.py',
+    code: [
+      'from langchain_core.prompts import ChatPromptTemplate',
+      'from langchain_core.output_parsers import StrOutputParser',
+      'from langchain.chat_models import init_chat_model',
+      '',
+      'prompt = ChatPromptTemplate.from_messages([',
+      '    ("system", "You are a {style} assistant."),',
+      '    ("human", "{question}"),',
+      '])',
+      'model = init_chat_model("openai:gpt-4.1-mini")',
+      '',
+      '# prompt, model, parser -- все три реализуют Runnable',
+      '# Оператор | склеивает их в один chain',
+      'chain = prompt | model | StrOutputParser()',
+      '',
+      '# type(chain) -> RunnableSequence',
+      'print(type(chain).__name__)',
+      '',
+      '# invoke -> dict на вход, str на выход',
+      'print(chain.invoke({"style": "concise", "question": "What is LCEL?"}))',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'success',
+    text: 'Runnable -- единый контракт: invoke / batch / stream / ainvoke / abatch / astream / async stream.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/concepts/lcel/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 13);
+}
+
+module.exports = { createSlide };