Add CF_CONFIG env var for simpler Docker workflow

Config search order is now:
1. --config CLI option
2. CF_CONFIG environment variable
3. ./compose-farm.yaml
4. ~/.config/compose-farm/compose-farm.yaml

Docker workflow simplified: mount compose_dir once, set CF_CONFIG
to config file within it. No more symlink issues or multiple mounts.

README.md

@@ -134,6 +134,12 @@ pip install compose-farm
 
 <details><summary>🐳 Docker</summary>
 
+Using the provided `docker-compose.yml`:
+```bash
+docker compose run --rm cf up --all
+```
+
+Or directly:
 ```bash
 docker run --rm \
   -v $SSH_AUTH_SOCK:/ssh-agent -e SSH_AUTH_SOCK=/ssh-agent \
@@ -141,11 +147,6 @@ docker run --rm \
   ghcr.io/basnijholt/compose-farm up --all
 ```
 
-Or create an alias:
-```bash
-alias cf='docker run --rm -v $SSH_AUTH_SOCK:/ssh-agent -e SSH_AUTH_SOCK=/ssh-agent -v ./compose-farm.yaml:/root/.config/compose-farm/compose-farm.yaml:ro ghcr.io/basnijholt/compose-farm'
-```
-
 </details>
 
 ## Configuration

docker-compose.yml

@@ -0,0 +1,11 @@
+services:
+  cf:
+    image: ghcr.io/basnijholt/compose-farm:latest
+    volumes:
+      - ${SSH_AUTH_SOCK}:/ssh-agent:ro
+      # Compose directory (contains compose files AND compose-farm.yaml config)
+      - ${CF_COMPOSE_DIR:-/opt/compose}:${CF_COMPOSE_DIR:-/opt/compose}
+    environment:
+      - SSH_AUTH_SOCK=/ssh-agent
+      # Config file path (state stored alongside it)
+      - CF_CONFIG=${CF_COMPOSE_DIR:-/opt/compose}/compose-farm.yaml

src/compose_farm/config.py

@@ -148,9 +148,10 @@ def load_config(path: Path | None = None) -> Config:
     """Load configuration from YAML file.
 
     Search order:
-    1. Explicit path if provided
-    2. ./compose-farm.yaml
-    3. $XDG_CONFIG_HOME/compose-farm/compose-farm.yaml (defaults to ~/.config)
+    1. Explicit path if provided via --config
+    2. CF_CONFIG environment variable
+    3. ./compose-farm.yaml
+    4. $XDG_CONFIG_HOME/compose-farm/compose-farm.yaml (defaults to ~/.config)
     """
     search_paths = [
         Path("compose-farm.yaml"),
@@ -159,6 +160,8 @@ def load_config(path: Path | None = None) -> Config:
 
     if path:
         config_path = path
+    elif env_path := os.environ.get("CF_CONFIG"):
+        config_path = Path(env_path)
     else:
         config_path = None
         for p in search_paths:
@@ -170,6 +173,13 @@ def load_config(path: Path | None = None) -> Config:
         msg = f"Config file not found. Searched: {', '.join(str(p) for p in search_paths)}"
         raise FileNotFoundError(msg)
 
+    if config_path.is_dir():
+        msg = (
+            f"Config path is a directory, not a file: {config_path}\n"
+            "This often happens when Docker creates an empty directory for a missing mount."
+        )
+        raise FileNotFoundError(msg)
+
     with config_path.open() as f:
         raw = yaml.safe_load(f)