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-20.js

@@ -0,0 +1,56 @@
+// Slide 20: create_agent -- the unified agent entry point (v1.0)
+// Code slide: a working agent in 10 lines.
+
+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: 'Agents',
+    title: 'create_agent -- один вход для всех агентов',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/agent_basic.py',
+    code: [
+      'from langchain.agents import create_agent',
+      'from langchain.tools import tool',
+      '',
+      '@tool',
+      'def get_weather(city: str) -> str:',
+      '    """Get weather for a city."""',
+      '    return f"Sunny, 22C in {city}"',
+      '',
+      '# Один вызов вместо create_react_agent / create_openai_functions_agent / ...',
+      'agent = create_agent(',
+      '    model="openai:gpt-4.1",',
+      '    tools=[get_weather],',
+      '    system_prompt="You are a weather assistant.",',
+      ')',
+      '',
+      '# invoke -> dict {"messages": [...]}; последнее сообщение = ответ',
+      'result = agent.invoke({"messages": [{"role": "user",',
+      '    "content": "weather in Paris?"}]})',
+      'print(result["messages"][-1].content)',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'info',
+    text: 'Под капотом LangGraph-runtime: durable execution, checkpointing, human-in-the-loop доступны через middleware.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'docs.langchain.com/oss/python/langchain/agents',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 20);
+}
+
+module.exports = { createSlide };