fix(win): route shell-outs through a windowless helper (no cmd.exe flash)

_popen/_popen-style shell-outs flash a cmd.exe console window on Windows. Add
Platform::runHiddenCapture() — CreateProcess + CREATE_NO_WINDOW capturing stdout on
Windows, popen on POSIX — and route the remaining shell-outs through it:
- GPU-aware idle detection (getGpuUtilization: "where nvidia-smi" / "nvidia-smi --query-gpu")
- xmrig discovery + version (findXmrigBinary "where xmrig.exe"; "<bin> --version", stderr merged)
- wallet-rebuild helper (app_network) — keeps its exit-code check via the new exitCode out-param

None of these are on the launch path (that was the daemon spawn, fixed in a2f84be); each
would flash a console only when it ran (idle-GPU mining, mining tab, wallet recovery).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app_network.cpp

@@ -5043,21 +5043,12 @@ void App::rebuildWalletDatabase()
                 const std::string tmpOut = datadir + "/wallet.rebuilt-" + std::string(ts) + ".tmp";
                 { std::error_code ec; fs::remove(tmpOut, ec); }   // helper uses DB_EXCL — path must be fresh
 
-                // 3. Run the helper (src -> tmpOut). Quote both paths; capture its JSON line.
+                // 3. Run the helper (src -> tmpOut). Quote both paths; capture its JSON line. Windowless
-                std::string cmd = "\"" + helper + "\" \"" + src + "\" \"" + tmpOut + "\"";
+                //    (runHiddenCapture) so a wallet rebuild never flashes a cmd.exe console; it runs the
-#ifdef _WIN32
+                //    helper via CreateProcess directly on Windows, so no cmd.exe outer-quote wrap is needed.
-                cmd = "\"" + cmd + "\"";                          // cmd.exe strips the outermost quotes
+                const std::string cmd = "\"" + helper + "\" \"" + src + "\" \"" + tmpOut + "\"";
-                FILE* fp = _popen(cmd.c_str(), "r");
+                int rc = -1;
-#else
+                const std::string jout = util::Platform::runHiddenCapture(cmd, /*mergeStderr=*/false, &rc);
-                FILE* fp = popen(cmd.c_str(), "r");
-#endif
-                std::string jout;
-                if (fp) { char b[512]; while (std::fgets(b, sizeof b, fp)) jout += b; }
-#ifdef _WIN32
-                const int rc = fp ? _pclose(fp) : -1;
-#else
-                const int rc = fp ? pclose(fp) : -1;
-#endif
                 DEBUG_LOGF("[App] wallet-rebuild helper rc=%d out=%s\n", rc, jout.c_str());
 
                 // 4. Verify-before-swap: the output must be a readable BDB with the fund-critical keys.

src/daemon/xmrig_manager.cpp

@@ -23,6 +23,7 @@
 #include <curl/curl.h>
 
 #include "../util/logger.h"
+#include "../util/platform.h"
 #include "../util/pool_registry.h"
 
 #ifdef _WIN32
@@ -145,32 +146,18 @@ std::string XmrigManager::findXmrigBinary() {
         return path;
     }
 
-    // Fallback: system PATH
+    // Fallback: system PATH — windowless so it never flashes a console.
 #ifdef _WIN32
-    FILE* f = _popen("where xmrig.exe 2>nul", "r");
+    std::string out = util::Platform::runHiddenCapture("where xmrig.exe");
 #else
-    FILE* f = popen("which xmrig 2>/dev/null", "r");
+    std::string out = util::Platform::runHiddenCapture("which xmrig");
-#endif
-    if (f) {
-        char line[512];
-        if (fgets(line, sizeof(line), f)) {
-            std::string s(line);
-            while (!s.empty() && (s.back() == '\n' || s.back() == '\r'))
-                s.pop_back();
-            if (!s.empty() && fs::exists(s)) {
-#ifdef _WIN32
-                _pclose(f);
-#else
-                pclose(f);
-#endif
-                return s;
-            }
-        }
-#ifdef _WIN32
-        _pclose(f);
-#else
-        pclose(f);
 #endif
+    {
+        std::string s = out;
+        const auto nl = s.find_first_of("\r\n");   // first line only
+        if (nl != std::string::npos) s.erase(nl);
+        while (!s.empty() && (s.back() == ' ' || s.back() == '\t')) s.pop_back();
+        if (!s.empty() && fs::exists(s)) return s;
     }
 
     return {};
@@ -927,24 +914,10 @@ void XmrigManager::startVersionDetection()
         const bool binShellSafe =
             !bin.empty() && bin.find_first_of("\"'`$;&|<>^%\n\r") == std::string::npos;
         if (binShellSafe) {
-            const std::string cmd = "\"" + bin + "\" --version 2>&1";
+            // Windowless capture (mergeStderr: xmrig may print --version to stderr) — never flashes.
-#ifdef _WIN32
+            const std::string cmd = "\"" + bin + "\" --version";
-            FILE* fp = _popen(cmd.c_str(), "r");
+            const std::string out = util::Platform::runHiddenCapture(cmd, /*mergeStderr=*/true);
-#else
+            if (!out.empty()) ver = parseMinerVersion(out);
-            FILE* fp = popen(cmd.c_str(), "r");
-#endif
-            if (fp) {
-                std::string out;
-                char buf[256];
-                size_t n;
-                while ((n = fread(buf, 1, sizeof(buf), fp)) > 0) out.append(buf, n);
-#ifdef _WIN32
-                _pclose(fp);
-#else
-                pclose(fp);
-#endif
-                ver = parseMinerVersion(out);
-            }
         }
         std::lock_guard<std::mutex> lk(g_installed_ver_mutex);
         g_installed_ver = ver;

src/util/platform.cpp

@@ -867,6 +867,70 @@ int Platform::getSystemIdleSeconds()
 // GPU utilization detection
 // ============================================================================
 
+std::string Platform::runHiddenCapture(const std::string& cmdLine, bool mergeStderr, int* exitCode)
+{
+    if (exitCode) *exitCode = -1;
+#ifdef _WIN32
+    SECURITY_ATTRIBUTES sa;
+    ZeroMemory(&sa, sizeof(sa));
+    sa.nLength = sizeof(sa);
+    sa.bInheritHandle = TRUE;
+    HANDLE hRead = NULL, hWrite = NULL;
+    if (!CreatePipe(&hRead, &hWrite, &sa, 0)) return {};
+    SetHandleInformation(hRead, HANDLE_FLAG_INHERIT, 0);   // parent's read end stays private
+
+    HANDLE hNul = INVALID_HANDLE_VALUE;
+    if (!mergeStderr) {
+        hNul = CreateFileA("NUL", GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, &sa,
+                           OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+    }
+
+    STARTUPINFOA si;
+    ZeroMemory(&si, sizeof(si));
+    si.cb = sizeof(si);
+    si.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW;
+    si.wShowWindow = SW_HIDE;
+    si.hStdInput  = GetStdHandle(STD_INPUT_HANDLE);
+    si.hStdOutput = hWrite;
+    si.hStdError  = mergeStderr ? hWrite : hNul;
+
+    PROCESS_INFORMATION pi;
+    ZeroMemory(&pi, sizeof(pi));
+    std::string cl = cmdLine;   // CreateProcessA may modify lpCommandLine → needs a mutable buffer
+    std::string out;
+    if (CreateProcessA(NULL, cl.empty() ? NULL : &cl[0], NULL, NULL, TRUE,
+                       CREATE_NO_WINDOW, NULL, NULL, &si, &pi)) {
+        CloseHandle(hWrite); hWrite = NULL;   // close our copy so ReadFile hits EOF when the child exits
+        if (hNul != INVALID_HANDLE_VALUE) { CloseHandle(hNul); hNul = INVALID_HANDLE_VALUE; }
+        char buf[4096];
+        DWORD n = 0;
+        while (ReadFile(hRead, buf, sizeof(buf), &n, NULL) && n > 0) out.append(buf, n);
+        WaitForSingleObject(pi.hProcess, INFINITE);
+        if (exitCode) {
+            DWORD code = 0;
+            if (GetExitCodeProcess(pi.hProcess, &code)) *exitCode = static_cast<int>(code);
+        }
+        CloseHandle(pi.hProcess);
+        CloseHandle(pi.hThread);
+    }
+    if (hWrite != NULL) CloseHandle(hWrite);
+    if (hNul != INVALID_HANDLE_VALUE) CloseHandle(hNul);
+    CloseHandle(hRead);
+    return out;
+#else
+    const std::string full = cmdLine + (mergeStderr ? " 2>&1" : " 2>/dev/null");
+    std::string out;
+    FILE* f = popen(full.c_str(), "r");
+    if (!f) return out;
+    char buf[512];
+    size_t n;
+    while ((n = fread(buf, 1, sizeof(buf), f)) > 0) out.append(buf, n);
+    const int st = pclose(f);
+    if (exitCode) *exitCode = st;   // raw status (matches prior pclose-based rc checks)
+    return out;
+#endif
+}
+
 int Platform::getGpuUtilization()
 {
 #ifdef _WIN32
@@ -877,23 +941,16 @@ int Platform::getGpuUtilization()
     static bool s_has_nvidia = false;
     if (!s_tried_nvidia) {
         s_tried_nvidia = true;
-        FILE* f = _popen("where nvidia-smi 2>nul", "r");
+        // Windowless (runHiddenCapture) so GPU-aware idle detection never flashes a cmd.exe console.
-        if (f) {
+        const std::string w = runHiddenCapture("where nvidia-smi");
-            char buf[256];
+        s_has_nvidia = (w.find_first_not_of(" \t\r\n") != std::string::npos);
-            s_has_nvidia = (fgets(buf, sizeof(buf), f) != nullptr);
-            _pclose(f);
-        }
     }
     if (s_has_nvidia) {
-        FILE* f = _popen("nvidia-smi --query-gpu=utilization.gpu --format=csv,noheader,nounits 2>nul", "r");
+        const std::string o = runHiddenCapture(
-        if (f) {
+            "nvidia-smi --query-gpu=utilization.gpu --format=csv,noheader,nounits");
-            char buf[64];
+        if (!o.empty()) {
-            int util = -1;
+            int util = atoi(o.c_str());
-            if (fgets(buf, sizeof(buf), f)) {
+            if (util < 0 || util > 100) util = -1;
-                util = atoi(buf);
-                if (util < 0 || util > 100) util = -1;
-            }
-            _pclose(f);
             return util;
         }
     }

src/util/platform.h

@@ -179,6 +179,15 @@ public:
      * @return GPU busy percent, or -1 if unavailable.
      */
     static int getGpuUtilization();
+
+    // Run a command line and capture its stdout WITHOUT ever popping a console window: Windows uses
+    // CreateProcess + CREATE_NO_WINDOW (a plain popen()/_popen() flashes a cmd.exe console), POSIX uses
+    // popen(). Use this instead of _popen for anything run while the GUI is up. `mergeStderr` folds the
+    // child's stderr into the result (like "2>&1"); otherwise stderr is discarded. `exitCode`, if given,
+    // receives the child's exit status (raw pclose() status on POSIX, GetExitCodeProcess on Windows; -1
+    // if the process could not be launched).
+    static std::string runHiddenCapture(const std::string& cmdLine, bool mergeStderr = false,
+                                        int* exitCode = nullptr);
 };
 
 /**