docs(codex-plugin): use codex mcp add (the command that actually works)

Empirically reproduced (Codex CLI 0.133.0) — `codex plugin add` writes
[marketplaces.atlan] to ~/.codex/config.toml but does NOT write
[mcp_servers.atlan]. The plugin entry appears in Plugins → Manage but
the MCP server is never registered, so tool discovery returns 0 tools
and the agent silently falls back to spawning `codex exec` subprocesses.

`codex mcp add atlan --url https://mcp.atlan.com/mcp` writes the proper
[mcp_servers.atlan] section AND auto-launches the OAuth flow in one
step. No `--type` / `--transport` flag needed — Codex infers HTTP from
the URL.

Simplify the install section to one command that works. Keep the
"Once OpenAI's Plugin Directory is GA" stub for when the official
distribution path goes live.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: Aryamanz29

codex-plugin/README.md

@@ -4,40 +4,21 @@ Connects Atlan's hosted MCP server (`https://mcp.atlan.com/mcp`) to [OpenAI Code
 
 ## Install
 
-> **Note:** OpenAI's official Codex Plugin Directory is not yet GA. The build docs state: *"Adding plugins to the official Plugin Directory is coming soon. Self-serve plugin publishing and management are coming soon."* — see [developers.openai.com/codex/plugins/build](https://developers.openai.com/codex/plugins/build). Until then, Atlan customers install this plugin by registering Atlan's own marketplace — the steps below.
-
-### Sideload from this repository
-
-The repository root ships a marketplace manifest at `.agents/plugins/marketplace.json` that exposes the plugin as `atlan@atlan`.
-
 ```bash
-# Register Atlan's marketplace (point at the GitHub repo, or a local clone's root)
-codex plugin marketplace add https://github.com/atlanhq/agent-toolkit
-
-# Install the plugin from that marketplace
-codex plugin add atlan@atlan
+codex mcp add atlan --url https://mcp.atlan.com/mcp
 ```
 
-Quit and relaunch **Codex.app** — the Atlan plugin appears under **Plugins → Manage** (enabled, with the bundled MCP server registered). On first tool call, Codex runs OAuth against `mcp.atlan.com` to authenticate against your Atlan tenant.
+Codex detects OAuth support automatically and launches a browser tab to authenticate against `mcp.atlan.com` — no API keys or environment variables to manage. Quit and relaunch Codex (Cmd+Q the desktop app, or exit and re-run the CLI) after the auth flow completes so the new MCP server is loaded.
 
-### From the official Codex Plugin Directory (once GA)
+### Once OpenAI's Plugin Directory is GA
 
-When OpenAI opens self-serve publishing and Atlan is accepted into the curated Plugin Directory, install via **Codex.app → Plugins → search "Atlan" → Install**, or:
+OpenAI's [Codex Plugin Directory](https://developers.openai.com/codex/plugins/build) is not yet generally available. When self-serve publishing opens and Atlan is accepted, install via **Codex.app → Plugins → search "Atlan" → Install**, or:
 
 ```bash
 codex plugin add atlan@openai-curated
 ```
 
-### Direct MCP server install (CLI only, no plugin)
-
-If you only need the MCP server in the Codex CLI and don't care about the desktop-app plugin entry, run:
-
-```bash
-codex mcp add atlan --url https://mcp.atlan.com/mcp
-codex mcp login atlan
-```
-
-This appends `[mcp_servers.atlan]` to `~/.codex/config.toml` without going through the plugin system.
+This will register the plugin in **Plugins → Manage** with the Atlan logo and metadata, in addition to the MCP server entry.
 
 ## Verify