Add CanStartInstance method to check instance start conditions

pkg/manager/manager.go

@@ -21,6 +21,7 @@ type InstanceManager interface {
 	UpdateInstance(name string, options *instance.CreateInstanceOptions) (*instance.Process, error)
 	DeleteInstance(name string) error
 	StartInstance(name string) (*instance.Process, error)
+	CanStartInstance(inst *instance.Process) (bool, error)
 	StopInstance(name string) (*instance.Process, error)
 	RestartInstance(name string) (*instance.Process, error)
 	GetInstanceLogs(name string) (string, error)

pkg/manager/operations.go

@@ -201,6 +201,32 @@ func (im *instanceManager) StartInstance(name string) (*instance.Process, error)
 	return instance, nil
 }
 
+// CanStartInstance checks if an instance can be started.
+// An instance can be started if:
+//  1. It is not already running, AND
+//  2. Either:
+//     a) There is capacity (MaxRunningInstances is unlimited or not reached), OR
+//     b) The instance has on-demand start enabled AND LRU eviction is enabled
+//     (allowing older instances to be evicted to make room)
+func (im *instanceManager) CanStartInstance(inst *instance.Process) (bool, error) {
+	im.mu.RLock()
+	defer im.mu.RUnlock()
+
+	if inst == nil {
+		return false, fmt.Errorf("instance is nil")
+	}
+
+	if inst.IsRunning() {
+		return false, fmt.Errorf("instance with name %s is already running", inst.Name)
+	}
+
+	allowMaxRunning := im.instancesConfig.MaxRunningInstances == -1 || len(im.runningInstances) < im.instancesConfig.MaxRunningInstances
+	allowOnDemand := inst.GetOptions() != nil && inst.GetOptions().OnDemandStart != nil && *inst.GetOptions().OnDemandStart
+	allowLRUEviction := im.instancesConfig.EnableLRUEviction
+
+	return allowMaxRunning || (allowOnDemand && allowLRUEviction), nil
+}
+
 // StopInstance stops a running instance and returns it.
 func (im *instanceManager) StopInstance(name string) (*instance.Process, error) {
 	im.mu.RLock()