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

CONTRIBUTING.md

@@ -140,17 +140,15 @@ Skills are self-contained folders in the `skills/` directory that include a `SKI
 
 ### Adding Canvas Extensions
 
-Canvas extensions live in `extensions/<extension-id>/` and are installable through plugin metadata.
+Canvas extensions live in `extensions/<extension-id>/` as reusable source components. They are shipped only through plugin manifests in `plugins/`.
 
-1. **Create/update extension metadata**: Add `.github/plugin/plugin.json` in the extension folder
-2. **Use convention-based metadata**: Follow the extension plugin.json structure:
+1. **Create/update the extension source**: Add or update `extensions/<extension-id>/extension.mjs`
+2. **Register the extension plugin**: Add `plugins/<extension-id>/plugin.json`:
    - Required: `name` (matching folder name), `description`, `version`
    - Optional: `author`, `keywords`
-   - `logo` **must** be exactly `"assets/preview.png"` (enforced convention)
-   - `extensions` **must** be exactly `"."` (per [copilot-agent-runtime#9929](https://github.com/github/copilot-agent-runtime/pull/9929))
-   - **Never** include `x-awesome-copilot` field (use convention-based assets only)
+   - `extensions.com.github.copilot.logo` **must** be exactly `"assets/preview.png"`
 3. **Screenshot requirements**: Create `assets/preview.png` as your primary visual
-4. **Do not add `canvas.json`**: Extension website metadata is now sourced from `.github/plugin/plugin.json`
+4. **Do not add `canvas.json`**: Extension website metadata is sourced from the matching plugin manifest
 5. **Validate before submitting**: Run `npm run plugin:validate` to check compliance with conventions
 
 ### Adding Plugins
@@ -159,7 +157,7 @@ Plugins group related agents, commands, and skills around specific themes or wor
 
 1. **Create your plugin**: Run `npm run plugin:create` to scaffold a new plugin
 2. **Follow the naming convention**: Use descriptive, lowercase folder names with hyphens (e.g., `python-web-development`)
-3. **Define your content**: List agents, commands, and skills in `plugin.json` using the Claude Code spec fields
+3. **Define your content**: List agents, commands, hooks, skills, and reusable extensions under `extensions.com.github.awesome-copilot` in `plugin.json`
 4. **Test your plugin**: Run `npm run plugin:validate` to verify your plugin structure
 
 #### Creating a plugin
@@ -172,16 +170,17 @@ npm run plugin:create -- --name my-plugin-id
 
 ```
 plugins/my-plugin-id/
-├── .github/plugin/plugin.json  # Plugin metadata (Claude Code spec format)
+├── plugin.json                # Plugin metadata
 └── README.md                   # Plugin documentation
 ```
 
-> **Note:** Plugin content is defined declaratively in plugin.json using Claude Code spec fields (`agents`, `commands`, `skills`). Source files live in top-level directories and are materialized into plugins by CI.
+> **Note:** Plugin content is defined declaratively in plugin.json under `extensions.com.github.awesome-copilot`. Source files live in top-level directories and are materialized into plugins by CI. This repository namespace is removed from the served manifest.
 
 #### plugin.json example
 
 ```json
 {
+  "$schema": "https://agent-plugins.org/schemas/1.0.0/plugin.schema.json",
   "name": "my-plugin-id",
   "description": "Plugin description",
   "version": "1.0.0",
@@ -189,17 +188,21 @@ plugins/my-plugin-id/
   "author": { "name": "Awesome Copilot Community" },
   "repository": "https://github.com/github/awesome-copilot",
   "license": "MIT",
-  "agents": ["./agents/my-agent.md"],
-  "commands": ["./commands/my-command.md"],
-  "skills": ["./skills/my-skill/"]
+  "extensions": {
+    "com.github.awesome-copilot": {
+      "agents": ["./agents/my-agent.md"],
+      "commands": ["./commands/my-command.md"],
+      "skills": ["./skills/my-skill/"]
+    }
+  }
 }
 ```
 
 #### Plugin Guidelines
 
-- **Declarative content**: Plugin content is specified via `agents`, `commands`, and `skills` arrays in plugin.json — source files live in top-level directories and are materialized into plugins by CI
+- **Declarative content**: Plugin content is specified under `extensions.com.github.awesome-copilot` — source files live in top-level directories and are materialized into plugins by CI
 - **Valid references**: All paths referenced in plugin.json must point to existing source files in the repository
-- **Optional extension links**: Curated plugins can reference extensions using `x-awesome-copilot.extensions` with paths like `./extensions/<extension-id>`
+- **Reusable extensions**: Curated plugins can bundle extensions by adding `./extensions/<name>` paths under `extensions.com.github.awesome-copilot.extensions`; the same extension can be listed by multiple plugins
 - **Instructions excluded**: Instructions are standalone resources and are not part of plugins
 - **Clear purpose**: The plugin should solve a specific problem or workflow
 - **Validate before submitting**: Run `npm run plugin:validate` to ensure your plugin is valid