fix: write wasm build output to the reported artifact path

internal/service/build/service.go

@@ -85,15 +85,26 @@ func (s *Service) Wasm(ctx context.Context, options WasmOptions) (WasmResult, er
 	if err := s.fs.MkdirAll(outDir, 0o755); err != nil {
 		return WasmResult{}, err
 	}
+	compileArtifact, err := filepath.Abs(artifact)
+	if err != nil {
+		return WasmResult{}, fmt.Errorf("resolve artifact path: %w", err)
+	}
 
 	entry := defaultString(options.Entry, project.Entry)
 	compiler := "go"
 	if options.TinyGo {
 		compiler = "tinygo"
 	}
-	if err := s.compile(ctx, compiler, options.Path, entry, artifact, options.Optimize); err != nil {
+	if err := s.compile(ctx, compiler, options.Path, entry, compileArtifact, options.Optimize); err != nil {
 		return WasmResult{}, err
 	}
+	exists, err := s.fs.Exists(artifact)
+	if err != nil {
+		return WasmResult{}, err
+	}
+	if !exists {
+		return WasmResult{}, fmt.Errorf("wasm build reported success but artifact is missing: %s", artifact)
+	}
 
 	files := []string{artifact}
 	if !options.NoShim {

internal/service/build/service_test.go

@@ -0,0 +1,99 @@
+package build
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/paolo/flare-edge-cli/internal/domain/config"
+	"github.com/paolo/flare-edge-cli/internal/infra/configstore"
+	"github.com/paolo/flare-edge-cli/internal/infra/process"
+	"github.com/paolo/flare-edge-cli/internal/infra/toolchain"
+	"github.com/paolo/flare-edge-cli/internal/support/fs"
+)
+
+type fakeRunner struct {
+	last process.Command
+}
+
+func (r *fakeRunner) Run(_ context.Context, cmd process.Command) (process.Result, error) {
+	r.last = cmd
+
+	output := ""
+	for index := 0; index+1 < len(cmd.Args); index++ {
+		if cmd.Args[index] == "-o" {
+			output = cmd.Args[index+1]
+			break
+		}
+	}
+	if output == "" {
+		return process.Result{}, nil
+	}
+	if !filepath.IsAbs(output) {
+		output = filepath.Join(cmd.Dir, output)
+	}
+	if err := os.MkdirAll(filepath.Dir(output), 0o755); err != nil {
+		return process.Result{}, err
+	}
+	if err := os.WriteFile(output, []byte("wasm"), 0o644); err != nil {
+		return process.Result{}, err
+	}
+	return process.Result{}, nil
+}
+
+func (r *fakeRunner) Stream(_ context.Context, _ process.Command, _, _ io.Writer) error {
+	return nil
+}
+
+func TestWasmUsesStableArtifactPathAndRequiresArtifact(t *testing.T) {
+	tmpDir := t.TempDir()
+	projectDir := filepath.Join(tmpDir, "services", "orchestrator")
+	filesystem := fs.New()
+	store := configstore.New(filesystem)
+
+	project := config.DefaultProject("orchestrator", "github.com/paolo/orchestrator", "main", "edge-http", config.DefaultCompatibilityDate, "")
+	if err := store.SaveProject(projectDir, project); err != nil {
+		t.Fatalf("save project: %v", err)
+	}
+
+	runner := &fakeRunner{}
+	service := NewService(store, filesystem, runner, &toolchain.GoToolchain{})
+
+	result, err := service.Wasm(context.Background(), WasmOptions{
+		Path:   projectDir,
+		NoShim: true,
+	})
+	if err != nil {
+		t.Fatalf("build wasm: %v", err)
+	}
+
+	expectedArtifact := filepath.Join(projectDir, "dist", "app.wasm")
+	if result.Artifact != expectedArtifact {
+		t.Fatalf("unexpected artifact path: %q", result.Artifact)
+	}
+	outputIndex := -1
+	for index := 0; index+1 < len(runner.last.Args); index++ {
+		if runner.last.Args[index] == "-o" {
+			outputIndex = index + 1
+			break
+		}
+	}
+	if outputIndex == -1 {
+		t.Fatalf("expected -o flag in args: %v", runner.last.Args)
+	}
+	if !filepath.IsAbs(runner.last.Args[outputIndex]) {
+		t.Fatalf("compiler output path should be absolute, got %q", runner.last.Args[outputIndex])
+	}
+	if runner.last.Args[outputIndex] != expectedArtifact {
+		t.Fatalf("unexpected compiler output path: %q", runner.last.Args[outputIndex])
+	}
+	exists, err := filesystem.Exists(expectedArtifact)
+	if err != nil {
+		t.Fatalf("stat artifact: %v", err)
+	}
+	if !exists {
+		t.Fatalf("expected artifact to exist at %s", expectedArtifact)
+	}
+}