feat(01-01): generate and build hello app from manifest

- Add summer build with validated summer.yaml codegen
- Generate stable main.go and plugins.gen.go then go build
- Smoke-test the built hello binary greeter:hello command

examples/hello/hello_test.go

@@ -2,6 +2,9 @@ package main
 
 import (
 	"bytes"
+	"crypto/sha256"
+	"os"
+	"os/exec"
 	"strings"
 	"testing"
 )
@@ -15,3 +18,46 @@ func TestGreeterHelloPrintsAppName(t *testing.T) {
 		t.Fatalf("output = %q, want %q", got, "hello-app")
 	}
 }
+
+func TestBuiltBinaryGreeterHello(t *testing.T) {
+	first := runSummerBuild(t)
+	h1 := generatedHash(t)
+	second := runSummerBuild(t)
+	h2 := generatedHash(t)
+	if h1 != h2 {
+		t.Fatalf("generated files changed on second build\nfirst:\n%s\nsecond:\n%s", first, second)
+	}
+
+	cmd := exec.Command("./bin/hello", "greeter:hello")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("bin/hello greeter:hello: %v\n%s", err, out)
+	}
+	if got := strings.TrimSpace(string(out)); got != "hello-app" {
+		t.Fatalf("output = %q, want %q", got, "hello-app")
+	}
+}
+
+func runSummerBuild(t *testing.T) string {
+	t.Helper()
+	cmd := exec.Command("go", "run", "../../cmd/summer", "build")
+	cmd.Dir = "."
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("summer build: %v\n%s", err, out)
+	}
+	return string(out)
+}
+
+func generatedHash(t *testing.T) [32]byte {
+	t.Helper()
+	var buf bytes.Buffer
+	for _, name := range []string{"main.go", "plugins.gen.go"} {
+		body, err := os.ReadFile(name)
+		if err != nil {
+			t.Fatal(err)
+		}
+		buf.Write(body)
+	}
+	return sha256.Sum256(buf.Bytes())
+}