Migrate plugins and canvas extensions to Agent Plugins spec (#2546)

* feat: migrate plugins and extensions to Agent Plugins v1.0.0 spec

- Add \ to all 69 curated plugin manifests
- Migrate all 18 extension manifests: add \, move logo into
  xtensions.com.github.copilot.logo namespace, remove top-level
  logo and string xtensions: '.'
- Update eng/validate-plugins.mjs: require \, validate
  namespace-keyed extensions object for canvas extensions, widen
  name pattern to allow dots (spec §5.5, max 64 chars)
- Update eng/materialize-plugins.mjs: emit spec-clean served manifests
  (only spec fields: \, name, version, description, author,
  homepage, repository, license, keywords, extensions)
- Update eng/generate-website-data.mjs: read logo from namespace
  with fallback to top-level logo for compatibility
- Update eng/create-plugin.mjs: scaffold emits \
- Add .github/workflows/validate-plugins.yml: blocking CI for PRs
  touching plugins/** or extensions/**
- Add spec compliance check to external plugin quality gates:
  non-blocking warnings with ✅/⚠️/🛑 emoji legend
- Update AGENTS.md: document new extension manifest shape,
  add \ to plugin checklist

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* refactor: consolidate canvas extension plugins

- Move all extension plugin manifests from extensions/<name> to plugins/<name>
- Keep extensions/<name> as reusable source only
- Remove standalone extension discovery from marketplace and website plugin catalogs
- Auto-bundle same-name extension sources during materialization
- Add build-only extensions.json references for sharing extensions across plugins
- Remove x-awesome-copilot extension metadata support
- Update validation and contributor documentation

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* feat: add canvas extension scaffolding skill

- Add repo-local skill for creating canvas extension sources
- Generate spec-compliant plugin manifests under plugins/
- Support registering reusable extensions with multiple plugins
- Remove guidance for extension-local plugin manifests and custom fields

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* fix: align extension namespaces with current guidance

- Use each extension ID as its manifest namespace key
- Update validation and website generation to resolve extension-specific namespaces
- Upsert plugin validation PR comments using the existing repository pattern

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* fix: use Copilot extension namespace

- Adopt com.github.copilot for all canvas extension manifests
- Require the namespace during validation and website generation
- Update extension scaffolding guidance

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* docs: regenerate plugin catalog after merge

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* refactor(plugins): move manifests to plugin roots

Use root plugin.json manifests and namespaced extension directories throughout local tooling, validation, generation, and contributor documentation. Restore materialize-plugins.mjs line breaks so the source remains readable in GitHub.

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

Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* feat(plugins): migrate manifests to namespaced composition

Move repository composition metadata under com.github.awesome-copilot, materialize reusable extensions into the plugin extensions directory, and improve contributor and PR validation guidance.

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

Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* fix(validation): address plugin review findings

Restore executable build scripts, validate namespaced manifests and hook directories, improve README item counts, and manage validation comments across reruns.

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

Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

* Potential fix for pull request finding

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

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Copilot-Session: 8f3a88cb-e01e-4760-8125-460490dc1a76

eng/clean-materialized-plugins.mjs

@@ -64,7 +64,7 @@ function moveEntry(srcPath, destPath) {
 }
 
 export function restoreManifestFromMaterializedFiles(pluginPath) {
-  const pluginJsonPath = path.join(pluginPath, ".github/plugin", "plugin.json");
+  const pluginJsonPath = path.join(pluginPath, "plugin.json");
   if (!fs.existsSync(pluginJsonPath)) {
     return false;
   }
@@ -108,7 +108,7 @@ export function restoreManifestFromMaterializedFiles(pluginPath) {
 function cleanPlugin(pluginPath) {
   const manifestUpdated = restoreManifestFromMaterializedFiles(pluginPath);
   if (manifestUpdated) {
-    console.log(`  Updated ${path.basename(pluginPath)}/.github/plugin/plugin.json`);
+    console.log(`  Updated ${path.basename(pluginPath)}/plugin.json`);
   }
 
   let removed = 0;
@@ -126,7 +126,7 @@ function cleanPlugin(pluginPath) {
 }
 
 export function cleanMaterializedExtensionPlugin(extensionPath) {
-  const pluginJsonPath = path.join(extensionPath, ".github", "plugin", "plugin.json");
+  const pluginJsonPath = path.join(extensionPath, "plugin.json");
   let manifestUpdated = false;
   if (fs.existsSync(pluginJsonPath)) {
     const plugin = JSON.parse(fs.readFileSync(pluginJsonPath, "utf8"));
@@ -141,7 +141,7 @@ export function cleanMaterializedExtensionPlugin(extensionPath) {
     }
     if (manifestUpdated) {
       fs.writeFileSync(pluginJsonPath, JSON.stringify(plugin, null, 2) + "\n", "utf8");
-      console.log(`  Updated ${path.basename(extensionPath)}/.github/plugin/plugin.json`);
+      console.log(`  Updated ${path.basename(extensionPath)}/plugin.json`);
     }
   }
 
@@ -174,7 +174,7 @@ function isExtensionPluginDirectory(extensionPath) {
     return true;
   }
 
-  const pluginJsonPath = path.join(extensionPath, ".github", "plugin", "plugin.json");
+  const pluginJsonPath = path.join(extensionPath, "plugin.json");
   if (!fs.existsSync(pluginJsonPath)) {
     return false;
   }