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-17.js

@@ -0,0 +1,54 @@
+// Slide 17: RunnableParallel + RunnableBranch -- fan-out / conditional routing
+// Code slide: parallel execution and if/else logic in a chain.
+
+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: 'Runnable helpers',
+    title: 'Parallel + Branch -- fan-out и роутинг',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/runnable_parallel.py',
+    code: [
+      'from langchain_core.runnables import RunnableParallel, RunnableBranch',
+      '',
+      '# Parallel -- один вход, несколько параллельных Runnable-ов, dict на выходе',
+      'joke_chain = ChatPromptTemplate.from_template("Tell a joke about {topic}") | model',
+      'poem_chain = ChatPromptTemplate.from_template("Write a poem about {topic}") | model',
+      '',
+      'parallel = RunnableParallel(joke=joke_chain, poem=poem_chain)',
+      'result = parallel.invoke({"topic": "cats"})',
+      'print(result.keys())  # dict_keys(["joke", "poem"])',
+      '',
+      '# Branch -- if/else роутинг по условию',
+      'branch = RunnableBranch(',
+      '    (lambda x: "code" in x["topic"].lower(), code_chain),',
+      '    (lambda x: "math" in x["topic"].lower(), math_chain),',
+      '    general_chain,  # default',
+      ')',
+      'print(branch.invoke({"topic": "code review"}))',
+    ].join('\n'),
+  });
+
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'success',
+    text: 'RunnableParallel выполняется параллельно -- отлично для multi-aspect анализа (sentiment + summary + keywords).',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'python.langchain.com/docs/how_to/branching/',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 17);
+}
+
+module.exports = { createSlide };