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-09.js

@@ -0,0 +1,61 @@
+// Slide 09: MessagesPlaceholder + few-shot examples
+// Code slide: how to inject conversation history and demonstration examples.
+
+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: 'Prompts',
+    title: 'MessagesPlaceholder + few-shot',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/prompt_fewshot.py',
+    code: [
+      'from langchain_core.prompts import (',
+      '    ChatPromptTemplate, MessagesPlaceholder, FewShotChatMessagePromptTemplate,',
+      ')',
+      '',
+      '# Few-shot блок: примеры "вопрос -> ответ"',
+      'examples = [',
+      '    {"input": "2+2", "output": "4"},',
+      '    {"input": "3*3", "output": "9"},',
+      ']',
+      'example_prompt = ChatPromptTemplate.from_messages([',
+      '    ("human", "{input}"),',
+      '    ("ai", "{output}"),',
+      '])',
+      'few_shot = FewShotChatMessagePromptTemplate(',
+      '    example_prompt=example_prompt, examples=examples,',
+      ')',
+      '',
+      '# Сборка: system + few-shot + история + текущий вопрос',
+      'prompt = ChatPromptTemplate.from_messages([',
+      '    ("system", "You are a math assistant."),',
+      '    few_shot,',
+      '    MessagesPlaceholder("history"),',
+      '    ("human", "{question}"),',
+      '])',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'success',
+    text: 'MessagesPlaceholder("history") -- дырка, в которую при invoke подставляется список прошлых сообщений.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/how_to/few_shot_examples_chat/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 9);
+}
+
+module.exports = { createSlide };