docs(retrieval): document optional local layer

docs/plugins.md

@@ -12,7 +12,7 @@ Codex's local `plugins` and `marketplaces` tables survive configuration synchron
 
 Codex receives Caveman through its native plugin adapter. Humanizer, Impeccable, and Anthropic Frontend Design are downloaded as skill payloads from the GitHub sources in the manifest, without running upstream installers. All three appear in the extension selector for Codex. Ownership is recorded in `~/.my-ai-configuration/extensions.json`. Skill files are tracked by hash; modified or foreign files are retained with a warning. Existing installations from before ownership tracking are not automatically adopted.
 
-Normal installation and update also ask whether to update the selected client CLIs and enable Flashbang. Quickupdate reuses the saved shell, client, CLI update, Flashbang, and extension choices without opening menus. Only successful runs save selections; dry runs do not update CLIs or extensions.
+Normal installation and update also ask whether to update the selected client CLIs, enable Flashbang, and enable the optional Qwen3-Embedding-0.6B semantic retrieval layer. Retrieval is shared by Codex and Claude through a local MCP server, uses a per-user virtual environment and index, and is disabled by default. Quickupdate reuses the saved shell, client, CLI update, Flashbang, retrieval, and extension choices without opening menus. Disabling retrieval removes its setup-owned runtime, index, and MCP registrations. Only successful runs save selections; dry runs do not update CLIs, extensions, or retrieval.
 
 Plugin installation requires the corresponding client CLI, network access, and any authentication required by the plugin. Context7 may open an OAuth flow. Codex or plugin hooks may require a trust review in `/hooks`. The scripts never install plugins during a build or doctor run and never install them when `--dry-run` or `-DryRun` is used.