COMFY_DIR alone manages ComfyUI: derive the launch command from the standard venv layout

internal/config/config.go

@@ -51,11 +51,14 @@ type Config struct {
 	LLMBusyStatus  int
 	BusyRetryAfter int
 
-	// ComfyCmd spawns and supervises a ComfyUI server on demand (empty =
-	// unmanaged, the current behavior). ComfyDir is its working directory.
-	// The managed server is stopped after ComfyIdleTimeout without
-	// requests, freeing its VRAM; ComfyStartTimeout bounds how long a
-	// request waits for it to come up.
+	// ComfyCmd spawns and supervises a ComfyUI server on demand. When
+	// ComfyCmd is empty but ComfyDir is set, management is enabled with the
+	// standard venv layout under ComfyDir (.venv + main.py or
+	// ComfyUI/main.py; --port from the COMFY_URL port) — ComfyCmd is the
+	// override for other layouts and doubles as the working directory when
+	// set explicitly. The managed server is stopped after ComfyIdleTimeout
+	// without requests, freeing its VRAM; ComfyStartTimeout bounds how long
+	// a request waits for it to come up.
 	ComfyCmd          string
 	ComfyDir          string
 	ComfyIdleTimeout  time.Duration
@@ -305,6 +308,9 @@ func Load(getenv func(string) string) (Config, error) {
 	if cfg.ComfyCmd != "" && cfg.ComfyURL == "" {
 		return cfg, fmt.Errorf("COMFY_CMD requires COMFY_URL to be set (the proxy needs somewhere to forward)")
 	}
+	if cfg.ComfyCmd == "" && cfg.ComfyDir != "" && cfg.ComfyURL == "" {
+		return cfg, fmt.Errorf("COMFY_DIR without COMFY_CMD requires COMFY_URL to be set (it enables the managed ComfyUI)")
+	}
 	if cfg.OllamaURL == "" && cfg.ComfyURL == "" {
 		return cfg, ErrNoConsumer
 	}