fix: security-audit remediation (15 findings), empty-wallet warning, and send/chat/console/shutdown UX

Security audit remediation (15 confirmed findings from the codebase audit):
- H-02: scrub+delete the decrypt-flow plaintext key export on ALL exit paths
  (RAII guard) and purge stale obsidiandecryptexport* files at startup.
- M-01/L-03/L-04/L-05/L-07: sodium_memzero the Set-PIN and encrypt-PIN worker
  passphrase/PIN copies, the RPC Basic-auth string (auth_), the exported/imported
  key buffers (App::wipeSecrets, called from ~App and before main's _Exit), and
  the first-run wizard "Skip" buffers.
- M-03/M-04/M-05/L-06: return locked COPIES from XmrigManager/EmbeddedDaemon
  getters (dedicated error_mutex_; DaemonController::lastError now by value),
  route xmrig last_error_ writes through a locked setter, and wrap
  shutdown_status_/wizard_stop_status_ in a locking GuardedStatus
  (wizard_stopping_external_ -> std::atomic).
- M-02: persist after a console send/shield/import in the lite backend.
- L-01: require the confirm click for z_shieldcoinbase/z_mergetoaddress.
- L-02: quote/escape each Windows daemon argv per the MSDN CommandLineToArgvW rules.
- L-08: pin json/tomlplusplus/libwebp FetchContent to immutable commit SHAs.
- I-01: extract updater archives from the already-verified in-memory buffer
  (no disk re-read TOCTOU).

Feature: warn once (full-node) when the active wallet loads empty while a sibling
wallet file in the datadir holds keys. A funded salvage wallet.<ts>.bak routes to
the recovery/Restore flow; a funded sibling .dat routes to the wallet manager.
Per-wallet-file dismissal; gated on synced + address-list-loaded to avoid false
positives on warm reconnect / spent-down wallets.

UX fixes:
- send: show the TOTAL balance (with a spendable "available" note) in the source
  dropdown and keep pending-change addresses visible.
- chat: insert emoji at the cursor position; restrict new-chat recipients to
  shielded (z) addresses.
- console: optional auto-focus of the command input on tab open (off by default).
- shutdown: when "stop external daemon" is on, keep the shutdown screen up until
  the external node actually exits, showing live status.

Adversarially reviewed; verified across full-node, lite, and Windows builds; tests pass.

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

src/daemon/xmrig_manager.cpp

@@ -210,7 +210,7 @@ bool XmrigManager::generateConfig(const Config& cfg, const std::string& outPath)
         fs::create_directories(fs::path(outPath).parent_path());
         std::ofstream ofs(outPath, std::ios::trunc);
         if (!ofs.is_open()) {
-            last_error_ = "Cannot write xmrig config: " + outPath;
+            setLastError("Cannot write xmrig config: " + outPath);
             DEBUG_LOGF("[ERROR] XmrigManager: %s\n", last_error_.c_str());
             return false;
         }
@@ -224,7 +224,7 @@ bool XmrigManager::generateConfig(const Config& cfg, const std::string& outPath)
         ofs.close();
         return true;
     } catch (const std::exception& e) {
-        last_error_ = std::string("Config write error: ") + e.what();
+        setLastError(std::string("Config write error: ") + e.what());
         DEBUG_LOGF("[ERROR] XmrigManager: %s\n", last_error_.c_str());
         return false;
     }
@@ -236,19 +236,22 @@ bool XmrigManager::generateConfig(const Config& cfg, const std::string& outPath)
 
 bool XmrigManager::start(const Config& cfg) {
     if (state_ == State::Running || state_ == State::Starting) {
-        last_error_ = "Already running";
+        setLastError("Already running");
         DEBUG_LOGF("[WARN] XmrigManager: %s\n", last_error_.c_str());
         return false;
     }
 
     state_ = State::Starting;
     should_stop_ = false;
-    last_error_.clear();
+    setLastError(std::string());
     {
         std::lock_guard<std::mutex> lk(output_mutex_);
         process_output_.clear();
     }
-    stats_ = PoolStats{};
+    {
+        std::lock_guard<std::mutex> lk(stats_mutex_);
+        stats_ = PoolStats{};
+    }
 
     // Extract pool hostname for stats API queries
     {
@@ -265,7 +268,7 @@ bool XmrigManager::start(const Config& cfg) {
     // Find binary
     std::string binary = findXmrigBinary();
     if (binary.empty()) {
-        last_error_ = "xmrig binary not found";
+        setLastError("xmrig binary not found");
         state_ = State::Error;
         DEBUG_LOGF("[ERROR] XmrigManager: xmrig binary not found\n");
         return false;
@@ -368,7 +371,7 @@ bool XmrigManager::startProcess(const std::string& xmrigPath, const std::string&
 
     HANDLE hRead = nullptr, hWrite = nullptr;
     if (!CreatePipe(&hRead, &hWrite, &sa, 0)) {
-        last_error_ = "CreatePipe failed";
+        setLastError("CreatePipe failed");
         DEBUG_LOGF("[ERROR] XmrigManager: %s\n", last_error_.c_str());
         return false;
     }
@@ -400,7 +403,7 @@ bool XmrigManager::startProcess(const std::string& xmrigPath, const std::string&
         char errBuf[256];
         FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                        NULL, err, 0, errBuf, sizeof(errBuf), NULL);
-        last_error_ = "CreateProcess failed for xmrig (error " + std::to_string(err) + "): " + errBuf;
+        setLastError("CreateProcess failed for xmrig (error " + std::to_string(err) + "): " + errBuf);
         DEBUG_LOGF("[ERROR] XmrigManager: %s\nCommand: %s\n", last_error_.c_str(), cmdLine.c_str());
         return false;
     }
@@ -451,14 +454,14 @@ void XmrigManager::drainOutput() {
 bool XmrigManager::startProcess(const std::string& xmrigPath, const std::string& cfgPath, int threads) {
     int pipefd[2];
     if (pipe(pipefd) != 0) {
-        last_error_ = "pipe() failed";
+        setLastError("pipe() failed");
         DEBUG_LOGF("[ERROR] XmrigManager: %s\n", last_error_.c_str());
         return false;
     }
 
     pid_t pid = fork();
     if (pid < 0) {
-        last_error_ = "fork() failed";
+        setLastError("fork() failed");
         DEBUG_LOGF("[ERROR] XmrigManager: %s\n", last_error_.c_str());
         close(pipefd[0]);
         close(pipefd[1]);
@@ -629,7 +632,7 @@ void XmrigManager::monitorProcess() {
             if (GetExitCodeProcess(process_handle_, &exitCode) && exitCode != STILL_ACTIVE) {
                 DEBUG_LOGF("[ERROR] XmrigManager: process exited (code %lu)\n", exitCode);
                 state_ = State::Error;
-                last_error_ = "xmrig process exited unexpectedly";
+                setLastError("xmrig process exited unexpectedly");
                 break;
             }
         }
@@ -640,7 +643,7 @@ void XmrigManager::monitorProcess() {
             if (ret == process_pid_ || ret < 0) {
                 DEBUG_LOGF("[ERROR] XmrigManager: process exited (waitpid=%d)\n", ret);
                 state_ = State::Error;
-                last_error_ = "xmrig process exited unexpectedly";
+                setLastError("xmrig process exited unexpectedly");
                 break;
             }
         }