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/create-plugin.mjs

@@ -128,11 +128,11 @@ async function createPlugin() {
     }
 
     // Create directory structure
-    const githubPluginDir = path.join(pluginDir, ".github", "plugin");
-    fs.mkdirSync(githubPluginDir, { recursive: true });
+    fs.mkdirSync(pluginDir, { recursive: true });
 
     // Generate plugin.json
     const pluginJson = {
+      "$schema": "https://agent-plugins.org/schemas/1.0.0/plugin.schema.json",
       name: pluginId,
       description,
       version: "1.0.0",
@@ -140,10 +140,16 @@ async function createPlugin() {
       author: { name: "Awesome Copilot Community" },
       repository: "https://github.com/github/awesome-copilot",
       license: "MIT",
+      extensions: {
+        "com.github.awesome-copilot": {
+          agents: [],
+          skills: [],
+        },
+      },
     };
 
     fs.writeFileSync(
-      path.join(githubPluginDir, "plugin.json"),
+      path.join(pluginDir, "plugin.json"),
       JSON.stringify(pluginJson, null, 2) + "\n"
     );
 
@@ -176,7 +182,7 @@ MIT
     console.log(`\n✅ Created plugin: ${pluginDir}`);
     console.log("\n📝 Next steps:");
     console.log(`1. Add agents, prompts, or instructions to plugins/${pluginId}/`);
-    console.log(`2. Update plugins/${pluginId}/.github/plugin/plugin.json with your metadata`);
+    console.log(`2. Update plugins/${pluginId}/plugin.json with your metadata`);
     console.log(`3. Edit plugins/${pluginId}/README.md to describe your plugin`);
     console.log("4. Run 'npm run build' to regenerate documentation");
   } catch (error) {