Replace File System Access API save with dev server POST /save

⌘S now saves everything (slide content + notes) to disk via `server.js`,
no file picker dialogs, works in any browser. Start with `node server.js`.

Author: st0012

server.js

@@ -0,0 +1,80 @@
+// Dev server with save endpoint for the slide presentation.
+// Usage: node server.js [port]
+// Serves static files and accepts POST /save to write the HTML back to disk.
+
+const http = require('http');
+const fs = require('fs');
+const path = require('path');
+
+const PORT = parseInt(process.argv[2] || '8080', 10);
+const ROOT = __dirname;
+const SLIDE_FILE = path.join(ROOT, 'the-future-of-ruby-documentation.html');
+
+const MIME = {
+  '.html': 'text/html; charset=utf-8',
+  '.css': 'text/css',
+  '.js': 'application/javascript',
+  '.json': 'application/json',
+  '.png': 'image/png',
+  '.jpg': 'image/jpeg',
+  '.jpeg': 'image/jpeg',
+  '.gif': 'image/gif',
+  '.svg': 'image/svg+xml',
+  '.ico': 'image/x-icon',
+  '.woff2': 'font/woff2',
+  '.pdf': 'application/pdf',
+};
+
+const server = http.createServer((req, res) => {
+  // Save endpoint — writes the POST body to the slide file
+  if (req.method === 'POST' && req.url === '/save') {
+    const chunks = [];
+    req.on('data', chunk => chunks.push(chunk));
+    req.on('end', () => {
+      try {
+        fs.writeFileSync(SLIDE_FILE, Buffer.concat(chunks));
+        res.writeHead(200, {
+          'Content-Type': 'text/plain',
+          'Access-Control-Allow-Origin': '*',
+        });
+        res.end('saved');
+        console.log(`[${new Date().toLocaleTimeString()}] Saved ${path.basename(SLIDE_FILE)}`);
+      } catch (err) {
+        res.writeHead(500, { 'Content-Type': 'text/plain' });
+        res.end('Error: ' + err.message);
+        console.error('Save failed:', err.message);
+      }
+    });
+    return;
+  }
+
+  // Static file serving
+  const urlPath = decodeURIComponent(req.url.split('?')[0]);
+  let filePath = path.join(ROOT, urlPath === '/' ? 'the-future-of-ruby-documentation.html' : urlPath);
+  filePath = path.normalize(filePath);
+
+  // Prevent directory traversal
+  if (!filePath.startsWith(ROOT)) {
+    res.writeHead(403);
+    res.end('Forbidden');
+    return;
+  }
+
+  fs.readFile(filePath, (err, data) => {
+    if (err) {
+      res.writeHead(404, { 'Content-Type': 'text/plain' });
+      res.end('Not found: ' + urlPath);
+      return;
+    }
+    const ext = path.extname(filePath).toLowerCase();
+    res.writeHead(200, { 'Content-Type': MIME[ext] || 'application/octet-stream' });
+    res.end(data);
+  });
+});
+
+server.listen(PORT, () => {
+  console.log(`Dev server running at http://localhost:${PORT}`);
+  console.log(`Serving: ${ROOT}`);
+  console.log(`Save target: ${path.basename(SLIDE_FILE)}`);
+  console.log(`Press Ctrl+C to stop\n`);
+});

slides_outline.md

@@ -303,9 +303,24 @@ All supporting research is in `research/`:
 
 ## Working with the Slides
 
+### Dev Server
+
+Start the dev server (serves files + enables saving):
+
+```bash
+node server.js        # http://localhost:8080
+node server.js 3000   # custom port
+```
+
+Open `http://localhost:8080` in any browser. The slides are served as the default page.
+
 ### Editing
 
-Open `the-future-of-ruby-documentation.html` in a browser. Press **E** or hover the top-left corner to enter edit mode. Click any text to edit. **Ctrl+S** saves directly back to the file (Chrome/Edge only — first save prompts for file location, subsequent saves are instant).
+Press **E** or hover the top-left corner to enter edit mode. Click any text to edit. Press **N** to open the speaker notes editor. **⌘S** saves everything (slide content + notes) back to the file via the dev server — works from anywhere, any browser, no dialogs.
+
+### Presenter Mode
+
+Press **S** to open the presenter window (timer, current/next slide, speaker notes). Press **B** to blackout the main window.
 
 ### Exporting to PDF