Add missing plugins to marketplace.json and create automation script

- Add context-engineering, gem-team, and ospo-sponsorship to marketplace.json
- Create eng/generate-marketplace.mjs to automatically generate marketplace.json
- Update package.json build script to include marketplace generation
- Update GitHub workflow to trigger on plugin changes

Co-authored-by: aaronpowell <434140+aaronpowell@users.noreply.github.com>

eng/generate-marketplace.mjs

@@ -0,0 +1,99 @@
+#!/usr/bin/env node
+
+import fs from "fs";
+import path from "path";
+import { ROOT_FOLDER } from "./constants.mjs";
+
+const PLUGINS_DIR = path.join(ROOT_FOLDER, "plugins");
+const MARKETPLACE_FILE = path.join(ROOT_FOLDER, ".github", "plugin", "marketplace.json");
+
+/**
+ * Read plugin metadata from plugin.json file
+ * @param {string} pluginDir - Path to plugin directory
+ * @returns {object|null} - Plugin metadata or null if not found
+ */
+function readPluginMetadata(pluginDir) {
+  const pluginJsonPath = path.join(pluginDir, ".github", "plugin", "plugin.json");
+  
+  if (!fs.existsSync(pluginJsonPath)) {
+    console.warn(`Warning: No plugin.json found for ${path.basename(pluginDir)}`);
+    return null;
+  }
+  
+  try {
+    const content = fs.readFileSync(pluginJsonPath, "utf8");
+    return JSON.parse(content);
+  } catch (error) {
+    console.error(`Error reading plugin.json for ${path.basename(pluginDir)}:`, error.message);
+    return null;
+  }
+}
+
+/**
+ * Generate marketplace.json from plugin directories
+ */
+function generateMarketplace() {
+  console.log("Generating marketplace.json...");
+  
+  if (!fs.existsSync(PLUGINS_DIR)) {
+    console.error(`Error: Plugins directory not found at ${PLUGINS_DIR}`);
+    process.exit(1);
+  }
+  
+  // Read all plugin directories
+  const pluginDirs = fs.readdirSync(PLUGINS_DIR, { withFileTypes: true })
+    .filter(entry => entry.isDirectory())
+    .map(entry => entry.name)
+    .sort();
+  
+  console.log(`Found ${pluginDirs.length} plugin directories`);
+  
+  // Read metadata for each plugin
+  const plugins = [];
+  for (const dirName of pluginDirs) {
+    const pluginPath = path.join(PLUGINS_DIR, dirName);
+    const metadata = readPluginMetadata(pluginPath);
+    
+    if (metadata) {
+      plugins.push({
+        name: metadata.name,
+        source: `./plugins/${dirName}`,
+        description: metadata.description,
+        version: metadata.version || "1.0.0"
+      });
+      console.log(`✓ Added plugin: ${metadata.name}`);
+    } else {
+      console.log(`✗ Skipped: ${dirName} (no valid plugin.json)`);
+    }
+  }
+  
+  // Create marketplace.json structure
+  const marketplace = {
+    name: "awesome-copilot",
+    metadata: {
+      description: "Community-driven collection of GitHub Copilot plugins, agents, prompts, and skills",
+      version: "1.0.0",
+      pluginRoot: "./plugins"
+    },
+    owner: {
+      name: "GitHub",
+      email: "copilot@github.com"
+    },
+    plugins: plugins
+  };
+  
+  // Ensure directory exists
+  const marketplaceDir = path.dirname(MARKETPLACE_FILE);
+  if (!fs.existsSync(marketplaceDir)) {
+    fs.mkdirSync(marketplaceDir, { recursive: true });
+  }
+  
+  // Write marketplace.json
+  fs.writeFileSync(MARKETPLACE_FILE, JSON.stringify(marketplace, null, 2) + "\n");
+  
+  console.log(`\n✓ Successfully generated marketplace.json with ${plugins.length} plugins`);
+  console.log(`  Location: ${MARKETPLACE_FILE}`);
+}
+
+// Run the script
+generateMarketplace();