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-06.js

@@ -0,0 +1,53 @@
+// Slide 06: Messages -- HumanMessage, AIMessage, SystemMessage, ToolMessage
+// Code slide: the message contract, how to build multi-turn prompts.
+
+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: 'Messages',
+    title: 'Стандартизированные сообщения',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/messages.py',
+    code: [
+      'from langchain.messages import (',
+      '    HumanMessage, AIMessage, SystemMessage, ToolMessage,',
+      ')',
+      'from langchain.chat_models import init_chat_model',
+      '',
+      'model = init_chat_model("openai:gpt-4.1-mini")',
+      '',
+      'messages = [',
+      '    SystemMessage(content="You are a concise assistant."),',
+      '    HumanMessage(content="What is LCEL?"),',
+      '    AIMessage(content="LCEL = pipe-based composition in LangChain."),',
+      '    HumanMessage(content="Show a one-line example."),',
+      ']',
+      '',
+      'response = model.invoke(messages)',
+      'print(response.content)',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'info',
+    text: 'С v1.0 контент -- стандартизированные content blocks: reasoning traces, citations, tool_call блоки.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/concepts/messages/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 6);
+}
+
+module.exports = { createSlide };