Migrate extension plugin materialization to extensions container (#2334)

* Migrate extension plugin materialization layout

Materialize extension plugins into a dedicated extensions/ container, validate the new manifest convention, and bump extension plugin versions.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d26008fb-9928-4ba7-b7c8-36f35320f7c1

* Keep extension manifests source-compatible

Restore source extension manifests to "extensions": "." while preserving materialization-time rewrite to "extensions" in distribution output.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d26008fb-9928-4ba7-b7c8-36f35320f7c1

* Validate canvas extension layout for external submissions

Add intake and quality-gate checks for canvas-tagged external plugins so they must include extensions/extension.mjs and optional manifest extensions is validated when present.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d26008fb-9928-4ba7-b7c8-36f35320f7c1

* Fix plugin clean extension pass and typo guard text

Declare EXTENSIONS_DIR in clean-materialized-plugins and run extension cleanup once after plugin cleanup. Also normalize misspelled-key detection strings to satisfy spelling checks without changing validation behavior.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d26008fb-9928-4ba7-b7c8-36f35320f7c1

* Proper codespell fix

* Separate canvas structure quality gate status

Track canvas structure as its own gate status and output, include it in aggregate summaries, and enforce Git object types so extensions/ is a tree and extensions/extension.mjs is a blob.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: d26008fb-9928-4ba7-b7c8-36f35320f7c1

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

eng/materialize-plugins.mjs

@@ -2,9 +2,11 @@
 
 import fs from "fs";
 import path from "path";
+import { fileURLToPath } from "url";
 import { ROOT_FOLDER } from "./constants.mjs";
 
 const PLUGINS_DIR = path.join(ROOT_FOLDER, "plugins");
+const EXTENSIONS_DIR = path.join(ROOT_FOLDER, "extensions");
 
 /**
  * Recursively copy a directory.
@@ -22,6 +24,17 @@ function copyDirRecursive(src, dest) {
   }
 }
 
+function copyEntryRecursive(srcPath, destPath) {
+  const stats = fs.statSync(srcPath);
+  if (stats.isDirectory()) {
+    copyDirRecursive(srcPath, destPath);
+    return;
+  }
+
+  fs.mkdirSync(path.dirname(destPath), { recursive: true });
+  fs.copyFileSync(srcPath, destPath);
+}
+
 /**
  * Resolve a plugin-relative path to the repo-root source file.
  *
@@ -45,6 +58,48 @@ function resolveSource(relPath) {
   return null;
 }
 
+export function materializeExtensionPlugin(extensionPath) {
+  const pluginJsonPath = path.join(extensionPath, ".github", "plugin", "plugin.json");
+  if (!fs.existsSync(pluginJsonPath)) {
+    return { copiedEntries: 0, manifestUpdated: false, skipped: true };
+  }
+
+  let metadata;
+  try {
+    metadata = JSON.parse(fs.readFileSync(pluginJsonPath, "utf8"));
+  } catch (err) {
+    throw new Error(`Failed to parse ${pluginJsonPath}: ${err.message}`);
+  }
+
+  const extensionContainerPath = path.join(extensionPath, "extensions");
+  fs.rmSync(extensionContainerPath, { recursive: true, force: true });
+  fs.mkdirSync(extensionContainerPath, { recursive: true });
+
+  let copiedEntries = 0;
+  for (const entry of fs.readdirSync(extensionPath, { withFileTypes: true })) {
+    if (entry.name === ".github" || entry.name === "extensions") {
+      continue;
+    }
+
+    copyEntryRecursive(
+      path.join(extensionPath, entry.name),
+      path.join(extensionContainerPath, entry.name)
+    );
+    copiedEntries++;
+  }
+
+  let manifestUpdated = false;
+  if (metadata.extensions !== "extensions") {
+    metadata.extensions = "extensions";
+    manifestUpdated = true;
+  }
+  if (manifestUpdated) {
+    fs.writeFileSync(pluginJsonPath, JSON.stringify(metadata, null, 2) + "\n", "utf8");
+  }
+
+  return { copiedEntries, manifestUpdated, skipped: false };
+}
+
 function materializePlugins() {
   console.log("Materializing plugin files...\n");
 
@@ -61,6 +116,8 @@ function materializePlugins() {
   let totalAgents = 0;
   let totalSkills = 0;
   let totalExtensions = 0;
+  let totalExtensionPlugins = 0;
+  let totalExtensionPluginEntries = 0;
   let warnings = 0;
   let errors = 0;
 
@@ -185,7 +242,36 @@ function materializePlugins() {
     }
   }
 
-  console.log(`\nDone. Copied ${totalAgents} agents, ${totalSkills} skills, ${totalExtensions} extensions.`);
+  if (fs.existsSync(EXTENSIONS_DIR)) {
+    const extensionDirs = fs.readdirSync(EXTENSIONS_DIR, { withFileTypes: true })
+      .filter((entry) => entry.isDirectory())
+      .map((entry) => entry.name)
+      .sort();
+
+    for (const dirName of extensionDirs) {
+      const extensionPath = path.join(EXTENSIONS_DIR, dirName);
+      if (!fs.existsSync(path.join(extensionPath, "extension.mjs"))) {
+        continue;
+      }
+
+      try {
+        const result = materializeExtensionPlugin(extensionPath);
+        if (result.skipped) {
+          continue;
+        }
+
+        totalExtensionPlugins++;
+        totalExtensionPluginEntries += result.copiedEntries;
+        console.log(`✓ ${dirName}: materialized extension bundle into ./extensions (${result.copiedEntries} entries)`);
+      } catch (err) {
+        console.error(`Error: Failed to materialize extension plugin ${dirName}: ${err.message}`);
+        errors++;
+      }
+    }
+  }
+
+  console.log(`\nDone. Copied ${totalAgents} agents, ${totalSkills} skills, ${totalExtensions} plugin extension refs.`);
+  console.log(`Materialized ${totalExtensionPlugins} extension plugins (${totalExtensionPluginEntries} top-level entries).`);
   if (warnings > 0) {
     console.log(`${warnings} warning(s).`);
   }
@@ -195,4 +281,8 @@ function materializePlugins() {
   }
 }
 
-materializePlugins();
+export { materializePlugins };
+
+if (process.argv[1] && path.resolve(process.argv[1]) === fileURLToPath(import.meta.url)) {
+  materializePlugins();
+}