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

.github/skills/create-canvas-extension/SKILL.md

@@ -0,0 +1,124 @@
+---
+name: create-canvas-extension
+description: 'Create or register a canvas extension in the awesome-copilot repository. Use when asked to scaffold a new canvas extension, create its plugin.json, add a reusable extension to one or more plugins, or migrate extension metadata. Extensions are reusable source under extensions/; shippable plugin manifests belong under plugins/.'
+argument-hint: '[optional extension name or description]'
+---
+
+# Create a canvas extension
+
+Use this skill only for the `github/awesome-copilot` repository. Canvas extensions are reusable source components. They do not have a `plugin.json` under `extensions/`.
+
+## Required decisions
+
+Before creating files, ask for each missing value:
+
+1. **Extension ID**: lowercase kebab-case, matching the source folder and plugin name.
+2. **Display metadata**:
+   - description
+   - version (default `1.0.0`)
+   - author name and optional URL
+   - keywords (lowercase, hyphenated, maximum 10)
+   - repository and license (default to the repository URL and `MIT` when appropriate)
+3. **Canvas entrypoint**: confirm whether the extension already has `extension.mjs`. If not, create a minimal entrypoint only when the user provides enough implementation details; otherwise create the directory and leave an explicit TODO.
+4. **Preview image**: obtain an existing `assets/preview.png` path or ask the user to add it. Do not invent a binary image or silently use a misleading placeholder.
+5. **Plugin registration**:
+   - For a standalone installable canvas plugin, create `plugins/<extension-id>`.
+   - For an extension that belongs to an existing plugin, ask for the parent plugin ID and add `./extensions/<extension-id>` to that plugin's `extensions.com.github.awesome-copilot.extensions`.
+   - If the extension should be shipped by multiple plugins, collect all plugin IDs and add the same extension ID to each mapping file.
+
+## Files to create
+
+For a new extension plugin, create this structure:
+
+```text
+extensions/<extension-id>/
+├── extension.mjs
+└── assets/
+    └── preview.png
+
+plugins/<extension-id>/
+├── plugin.json
+└── README.md
+```
+
+The extension source may contain additional files such as `package.json`, canvas assets, or supporting modules. Keep all reusable implementation files under `extensions/<extension-id>/`.
+
+Create `plugins/<extension-id>/plugin.json` with this shape:
+
+```json
+{
+  "$schema": "https://agent-plugins.org/schemas/1.0.0/plugin.schema.json",
+  "name": "<extension-id>",
+  "description": "<description>",
+  "version": "1.0.0",
+  "author": {
+    "name": "<author>"
+  },
+  "repository": "https://github.com/github/awesome-copilot",
+  "license": "MIT",
+  "keywords": [
+    "<keyword>"
+  ],
+  "extensions": {
+    "com.github.copilot": {
+      "logo": "assets/preview.png"
+    },
+    "com.github.awesome-copilot": {
+      "extensions": [
+        "./extensions/<extension-id>"
+      ]
+    }
+  }
+}
+```
+
+Keep Agent Plugins fields at the manifest top level. Repository composition belongs only under `extensions.com.github.awesome-copilot`; do not put `agents`, `commands`, `hooks`, `mcpServers`, or `skills` at the top level or directly under `extensions`. Do not add `x-awesome-copilot`, `standalone`, or other repository-specific top-level fields.
+
+For an existing parent plugin, create or update:
+
+```text
+plugins/<parent-plugin>/plugin.json (`extensions.com.github.awesome-copilot.extensions`)
+```
+
+Its `extensions` property must contain sorted repository-relative paths:
+
+```json
+{
+  "extensions": [
+    "./extensions/<extension-id>"
+  ]
+}
+```
+
+Do not copy the extension source into the parent plugin. Materialization resolves the IDs from the root `extensions/` directory, so the same source can be bundled by multiple plugins.
+
+## Workflow
+
+1. Inspect the repository before editing:
+   - confirm `extensions/<extension-id>` and `plugins/<extension-id>` do not already conflict
+   - inspect the target parent plugin, if any
+   - check whether a preview image and entrypoint already exist
+2. Ask only the missing required questions from the decisions above.
+3. Create the source and plugin directories with the required files.
+4. If creating a new entrypoint, keep it minimal and clearly mark implementation TODOs rather than fabricating behavior.
+5. Add or update `extensions.com.github.awesome-copilot.extensions` for every parent plugin that should ship the extension. Keep paths alphabetically sorted and unique.
+6. Ensure there is no `extensions/<extension-id>/.github/plugin/plugin.json`.
+7. Run:
+
+   ```bash
+   npm run plugin:validate
+   npm run build
+   npm run website:data
+   ```
+
+8. Report the created paths, the plugins that ship the extension, and any missing user-provided assets or TODOs.
+
+## Existing extension migration
+
+When migrating an existing extension:
+
+1. Move its existing manifest to `plugins/<extension-id>/plugin.json`.
+2. Update the manifest to the namespace-based `extensions.com.github.copilot.logo` shape.
+3. Remove the old manifest from `extensions/<extension-id>`.
+4. Register the extension in any parent plugin's `extensions.com.github.awesome-copilot.extensions`.
+5. Run the validation and build commands above.