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-21.js

@@ -0,0 +1,58 @@
+// Slide 21: Short-term memory -- thread_id + checkpointer
+// Code slide: persistent conversation per thread.
+
+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: 'Memory',
+    title: 'Краткосрочная память: thread + checkpointer',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/memory_short.py',
+    code: [
+      'from langchain.agents import create_agent',
+      'from langgraph.checkpoint.memory import InMemorySaver',
+      '',
+      'checkpointer = InMemorySaver()',
+      '',
+      'agent = create_agent(',
+      '    model="openai:gpt-4.1-mini",',
+      '    tools=[...],',
+      '    checkpointer=checkpointer,  # <-- persistent state',
+      ')',
+      '',
+      'config = {"configurable": {"thread_id": "user-42"}}',
+      '',
+      '# Первый turn',
+      'agent.invoke({"messages": [{"role": "user",',
+      '    "content": "My name is Alice."}]}, config=config)',
+      '',
+      '# Второй turn -- модель помнит имя',
+      'result = agent.invoke({"messages": [{"role": "user",',
+      '    "content": "What is my name?"}]}, config=config)',
+      'print(result["messages"][-1].content)  # "Alice"',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'success',
+    text: 'InMemorySaver для dev. Для прода -- PostgresSaver / RedisSaver (те же LangGraph checkpointer-ы).',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'docs.langchain.com/oss/python/langgraph/persistence',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 21);
+}
+
+module.exports = { createSlide };