feat: add unofficial Codex plugin surface

.agents/plugins/marketplace.json

@@ -0,0 +1,20 @@
+{
+  "name": "slack-dev",
+  "interface": {
+    "displayName": "Slack (dev)"
+  },
+  "plugins": [
+    {
+      "name": "slack",
+      "source": {
+        "source": "local",
+        "path": "./"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "Productivity"
+    }
+  ]
+}

.changeset/add-codex-plugin-surface.md

@@ -0,0 +1,7 @@
+---
+"slack": minor
+---
+
+Add a Codex plugin surface. A new `.codex-plugin/plugin.json` manifest exposes the Slack skills to [Codex][codex], and a repo-scoped `.agents/plugins/marketplace.json` lets you install the plugin into Codex from a local checkout. The hosted MCP server is not yet wired into the Codex surface; skills only for now.
+
+[codex]: https://developers.openai.com/codex

.codex-plugin/plugin.json

@@ -0,0 +1,28 @@
+{
+  "name": "slack",
+  "version": "1.1.0",
+  "description": "Slack skills for building apps with the Slack CLI, Bolt, Web API, and Block Kit",
+  "author": {
+    "name": "Slack",
+    "url": "https://slack.com"
+  },
+  "homepage": "https://docs.slack.dev",
+  "repository": "https://github.com/slackapi/slack-skills-plugin",
+  "license": "MIT",
+  "skills": "./skills/",
+  "mcpServers": {},
+  "interface": {
+    "displayName": "Slack",
+    "shortDescription": "Slack skills for your AI tools",
+    "longDescription": "Skills for building Slack apps with the Slack CLI and Bolt, calling Web API methods, and composing Block Kit layouts, plus skills for searching and messaging in Slack when a Slack MCP server is connected.",
+    "defaultPrompt": "Help me build a Slack app with the Slack CLI and Bolt.",
+    "developerName": "Slack",
+    "category": "Productivity",
+    "capabilities": [
+      "Interactive",
+      "Read",
+      "Write"
+    ],
+    "websiteURL": "https://docs.slack.dev/ai/mcp-server/"
+  }
+}

.github/maintainers_guide.md

@@ -15,6 +15,8 @@ Maintaining this repo requires:
   Code rather than traditional CLI tooling.
 - **[Cursor][cursor]**: an alternative agentic coding environment. Useful for
   verifying that skills and commands work outside Claude Code before release.
+- **[Codex][codex-cli]**: another agentic coding environment. Useful for
+  verifying that the skills work outside Claude Code before release.
 - **Git**: standard version control.
 - **[GitHub CLI (`gh`)][gh-cli]**: for creating PRs as drafts and managing
   issues.
@@ -134,6 +136,30 @@ This copies the plugin into `~/.cursor/plugins/slack@local` and registers it.
 To remove it, run `make cursor-uninstall`. (`make clean` also runs the Cursor
 uninstall, in addition to removing the virtualenv and other generated files.)
 
+### Testing in Codex
+
+Codex loads plugins only from a marketplace. The repo ships a development marketplace at
+`.agents/plugins/marketplace.json` that points at this checkout, so you can add
+it as a local marketplace and install the plugin from it.
+
+Register the local marketplace and install the `slack` plugin:
+
+```sh
+codex plugin marketplace add ./
+codex plugin add slack@slack-dev
+```
+
+`codex plugin list` shows the plugin; `codex /plugins` opens the same flow interactively. Start a new Codex session to pick up the plugin, then invoke a skill by name with a `$` mention, for example `$block-kit`.
+
+To remove it
+
+```sh
+codex plugin remove slack@slack-dev
+codex plugin marketplace remove slack-dev
+```
+
+Codex support currently ships only the skills; the hosted MCP server is not yet wired into the Codex surface.
+
 ---
 
 ## Versioning
@@ -215,6 +241,7 @@ Patch and minor updates are auto-approved and auto-merged via the
 
 [claude-code]: https://claude.ai/code
 [cursor]: https://cursor.com
+[codex-cli]: https://developers.openai.com/codex/cli
 [gh-cli]: https://cli.github.com
 [conv-commits]: https://www.conventionalcommits.org
 [semver]: https://semver.org

scripts/sync_versions.py

@@ -11,6 +11,7 @@
 PACKAGE_JSON_PATH = REPO_ROOT / "package.json"
 CLAUDE_PLUGIN_PATH = REPO_ROOT / ".claude-plugin" / "plugin.json"
 CURSOR_PLUGIN_PATH = REPO_ROOT / ".cursor-plugin" / "plugin.json"
+CODEX_PLUGIN_PATH = REPO_ROOT / ".codex-plugin" / "plugin.json"
 
 
 def read_version(package_path: Path) -> str:
@@ -32,6 +33,7 @@ def main() -> None:
     version = read_version(PACKAGE_JSON_PATH)
     write_version(CLAUDE_PLUGIN_PATH, version)
     write_version(CURSOR_PLUGIN_PATH, version)
+    write_version(CODEX_PLUGIN_PATH, version)
 
 
 if __name__ == "__main__":