diff --git a/README.md b/README.md
index 2c39225..409398f 100644
--- a/README.md
+++ b/README.md
@@ -273,11 +273,17 @@ volumes:
   - devbox-vscode:/home/developer/.vscode-server
 ```
 
-### Shared machine setup (multiple users, single OS account)
+### Multi-user setup
 
-For machines where multiple users share one OS account (e.g. a common `garage` user), a separate compose file isolates each user's config and data using a `SIGNUM` variable.
+The shared-machine compose file (`docker-compose.shared.yml`) supports two modes:
 
-Each user creates their own directory and setup:
+**Own-account mode** (each user has their own OS login — the common case):
+Leave `SIGNUM` unset in `.env`. The project name defaults to `devbox-$USER`, so each OS user automatically gets isolated container names and named volumes with zero configuration.
+
+**Shared-account mode** (everyone logs in as the same OS user, e.g. `garage`):
+Each user sets `SIGNUM=<unique-id>` in `.env` to get isolation.
+
+Setup per user:
 
 ```bash
 # Replace <signum> with your username/identifier
@@ -291,17 +297,17 @@ cp /path/to/opencode-devbox/.env.shared.example .env
 # Create per-user config directory
 mkdir -p ~/<signum>/.config/opencode
 
-# Edit .env with your signum, provider, keys, etc.
+# Edit .env — set SIGNUM only if you're in shared-account mode
 vim .env
 
 # Start
 docker compose up -d
-docker compose exec -u developer devbox-<signum> opencode
+docker compose exec -u developer devbox opencode
 ```
 
 Each user's container, config, and named volumes are fully isolated:
-- Container name: `devbox-<signum>` (no collisions)
-- Named volumes: prefixed with the project directory name (automatic per-user isolation)
+- Container name: `devbox-<signum>` (or `devbox-$USER` in own-account mode)
+- Named volumes: prefixed with the project name (`devbox-<signum>_devbox-data`, etc.) — the Docker daemon is system-wide, so directory-name prefixing alone is NOT sufficient for isolation
 - Opencode config: `~/<signum>/.config/opencode/` (per-user settings, OMOS config, etc.)
 
 See `docker-compose.shared.yml` and `.env.shared.example` for the full configuration.