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-23.js

@@ -0,0 +1,60 @@
+// Slide 23: Middleware -- HumanInTheLoop + PIIRedaction + Summarization
+// Code slide: cross-cutting hooks attached at agent construction.
+
+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: 'Middleware',
+    title: 'Cross-cutting concerns одной строкой',
+    sectionNumber: 1,
+  });
+
+  ds.helpers.addCodeBlock(slide, pres, theme, {
+    x: 0.5, y: 1.5, w: 9.0, h: 3.25,
+    language: 'python',
+    filePath: 'examples/middleware.py',
+    code: [
+      'from langchain.agents import create_agent',
+      'from langchain.agents.middleware import (',
+      '    HumanInTheLoopMiddleware,',
+      '    PIIRedactionMiddleware,',
+      '    SummarizationMiddleware,',
+      ')',
+      'from langchain.tools import tool',
+      '',
+      '@tool',
+      'def send_email(to: str, body: str) -> str:',
+      '    """Send an email to recipient."""',
+      '    return f"sent to {to}"',
+      '',
+      'agent = create_agent(',
+      '    model="openai:gpt-4.1",',
+      '    tools=[send_email],',
+      '    middleware=[',
+      '        HumanInTheLoopMiddleware(interrupt_on={"send_email": True}),',
+      '        PIIRedactionMiddleware(redact_emails=True, redact_phones=True),',
+      '        SummarizationMiddleware(trigger=("tokens", 4000)),',
+      '    ],',
+      ')',
+    ].join('\n'),
+  });
+
+  // Right-side mini-glossary callouts (left side has code; reuse addCallout below)
+  ds.helpers.addCallout(slide, pres, theme, {
+    x: 0.5, y: 4.85, w: 9.0, h: 0.3,
+    kind: 'warning',
+    text: 'Все три middleware -- встроенные. Custom middleware пишутся как before_model/after_model hooks.',
+  });
+
+  ds.helpers.addSourceLine(slide, pres, theme, {
+    source: 'docs.langchain.com/oss/python/langchain/middleware',
+  });
+  ds.helpers.addPageNumber(slide, pres, theme, 23);
+}
+
+module.exports = { createSlide };