fix: better engine selector

Makefile

@@ -5,7 +5,7 @@ ifeq ($(DEBUG),1)
 	PIPER := $(PIPER) --log-level=debug
 endif
 
-#export PIPER_BUILDER_HOST =
+export PIPER_BUILDER_HOST =
 
 tidy:
 	$(PIPER) mod tidy

pkg/dagger/runner.go

@@ -104,26 +104,21 @@ type runner struct {
 	engines sync.Map
 }
 
-func (r *runner) ClientParams(scope *Scope) client.Params {
-	runnerHost := r.GetHost(scope.Platform)
-	p := r.Params
-	p.RunnerHost = runnerHost.RunnerHost
-	scope.ID = runnerHost.Name
-	return p
+func (r *runner) ClientParams(host string) client.Params {
+	return r.Hosts.ClientParams(host)
 }
 
 func (r *runner) Select(ctx context.Context, scope Scope) Engine {
 	if scope.Platform == "" {
 		scope.Platform = Platform(fmt.Sprintf("linux/%s", runtime.GOARCH))
 	}
-
-	if v, ok := r.engines.Load(scope.ID); ok {
-		return v.(Engine)
+	if scope.ID == "" {
+		scope.ID = r.GetHost(scope.Platform).Name
 	}
-
-	e := NewEngine(scope, r.ClientParams(&scope))
-	r.engines.Store(scope.ID, e)
-	return e
+	getEngine, _ := r.engines.LoadOrStore(scope.ID, sync.OnceValue(func() Engine {
+		return NewEngine(scope, r.ClientParams(scope.ID))
+	}))
+	return getEngine.(func() Engine)()
 }
 
 func (r *runner) Shutdown(ctx context.Context) error {
@@ -171,6 +166,22 @@ func (h *Hosts) AddHost(runnerHost *PiperRunnerHost) {
 	}
 }
 
+func (h *Hosts) ClientParams(name string) client.Params {
+	for _, hh := range h.Platformed {
+		for _, p := range hh {
+			if p.Name == name {
+				return client.Params{
+					RunnerHost: p.RunnerHost,
+				}
+			}
+		}
+	}
+
+	return client.Params{
+		RunnerHost: h.Default.RunnerHost,
+	}
+}
+
 func Select(ctx context.Context, scope Scope) Engine {
 	return RunnerContext.From(ctx).Select(ctx, scope)
 }