feat(recovery): bundle & embed the offline wallet-rebuild helper in every release

The dragonx-wallet-rebuild helper is the only thing that repairs a genuinely
BDB-inconsistent wallet.dat — plain "Restore" just re-triggers the daemon's
salvage cascade — yet it was silently dropped from every packaged build:

- Linux zip/AppImage copied a hand-picked file list that omitted it.
- Windows bundled it only behind a soft `[[ -f ]]` guard (silent skip).
- macOS never wired Berkeley DB, never built it, never bundled it.

build.sh now HARD-REQUIRES the helper for full-node releases (fails the build if
the vendored Berkeley DB depends are missing, rather than shipping recovery-less),
and ships it in the Linux zip + AppImage, the Windows zip, and the macOS .app.

It also compiles the helper standalone for Windows and INCBINs it, and
embedded_resources gains ensureWalletRebuildHelperExtracted() to extract it on
demand — so a self-contained ObsidianDragon.exe carries recovery exactly like the
embedded daemon, even on a machine where first-run param extraction already ran.

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

src/resources/embedded_resources.cpp

@@ -40,6 +40,9 @@ static const EmbeddedResource s_resources[] = {
     { g_dragonx_cli_exe_data,       g_dragonx_cli_exe_size,       RESOURCE_DRAGONX_CLI },
     { g_dragonx_tx_exe_data,        g_dragonx_tx_exe_size,        RESOURCE_DRAGONX_TX },
 #endif
+#ifdef HAS_EMBEDDED_WALLET_REBUILD
+    { g_dragonx_wallet_rebuild_exe_data, g_dragonx_wallet_rebuild_exe_size, RESOURCE_DRAGONX_WALLET_REBUILD },
+#endif
 #ifdef HAS_EMBEDDED_XMRIG
     { g_xmrig_exe_data,             g_xmrig_exe_size,             RESOURCE_XMRIG },
 #endif
@@ -436,6 +439,24 @@ bool extractEmbeddedResources()
     }
 #endif
 
+#ifdef HAS_EMBEDDED_WALLET_REBUILD
+    // Offline wallet-rebuild recovery helper — extracted next to the daemon so a bare, self-extracting
+    // ObsidianDragon.exe still offers "Repair automatically" (findWalletRebuildHelper() checks this dir).
+    const EmbeddedResource* rebuildRes = getEmbeddedResource(RESOURCE_DRAGONX_WALLET_REBUILD);
+    if (rebuildRes) {
+        std::string dest = daemonDir + pathSep + RESOURCE_DRAGONX_WALLET_REBUILD;
+        if (!std::filesystem::exists(dest)) {
+            DEBUG_LOGF("[INFO] Extracting dragonx-wallet-rebuild (%zu MB)...\n", rebuildRes->size / (1024*1024));
+            if (!extractResource(rebuildRes, dest)) {
+                success = false;
+            }
+#ifndef _WIN32
+            else { chmod(dest.c_str(), 0755); }
+#endif
+        }
+    }
+#endif
+
     // Best-effort cleanup of any ".old" binaries left behind by a previous in-use replacement.
     // Once the old daemon/xmrig process has exited, the file is no longer locked and removes cleanly;
     // if it's still running, the remove fails harmlessly and we retry on the next startup.
@@ -450,6 +471,32 @@ bool extractEmbeddedResources()
     return success;
 }
 
+std::string ensureWalletRebuildHelperExtracted()
+{
+#ifdef HAS_EMBEDDED_WALLET_REBUILD
+    const EmbeddedResource* res = getEmbeddedResource(RESOURCE_DRAGONX_WALLET_REBUILD);
+    if (!res || res->size == 0) return {};
+#ifdef _WIN32
+    const char sep = '\\';
+#else
+    const char sep = '/';
+#endif
+    const std::string dir  = getDaemonDirectory();
+    const std::string dest = dir + sep + RESOURCE_DRAGONX_WALLET_REBUILD;
+    std::error_code ec;
+    if (std::filesystem::exists(dest, ec)) return dest;   // already extracted
+    std::filesystem::create_directories(dir, ec);
+    if (!extractResource(res, dest)) return {};
+#ifndef _WIN32
+    chmod(dest.c_str(), 0755);
+#endif
+    DEBUG_LOGF("[INFO] Extracted wallet-rebuild helper on demand: %s\n", dest.c_str());
+    return dest;
+#else
+    return {};
+#endif
+}
+
 std::string getDaemonDirectory()
 {
     // Daemon binaries live in %APPDATA%/ObsidianDragon/dragonx/ (Windows) or

src/resources/embedded_resources.h

@@ -55,6 +55,12 @@ BundledDaemonInfo getBundledDaemonInfo();
 // caller should stop the daemon first. Returns true if all present resources were written.
 bool reextractBundledDaemon();
 
+// Ensure the embedded offline wallet-rebuild recovery helper is extracted to the daemon dir, and
+// return its path ("" if not embedded in this build or extraction failed). Idempotent — extracts only
+// when missing. Unlike the first-run extractEmbeddedResources() (gated on needsParamsExtraction()),
+// this runs on demand so recovery works from a self-contained exe on ANY run, not just the first.
+std::string ensureWalletRebuildHelperExtracted();
+
 // Resource names
 constexpr const char* RESOURCE_SAPLING_SPEND = "sapling-spend.params";
 constexpr const char* RESOURCE_SAPLING_OUTPUT = "sapling-output.params";
@@ -62,6 +68,7 @@ constexpr const char* RESOURCE_ASMAP = "asmap.dat";
 constexpr const char* RESOURCE_DRAGONXD = "dragonxd.exe";
 constexpr const char* RESOURCE_DRAGONX_CLI = "dragonx-cli.exe";
 constexpr const char* RESOURCE_DRAGONX_TX = "dragonx-tx.exe";
+constexpr const char* RESOURCE_DRAGONX_WALLET_REBUILD = "dragonx-wallet-rebuild.exe";
 constexpr const char* RESOURCE_XMRIG = "xmrig.exe";
 constexpr const char* RESOURCE_DARK_GRADIENT = "dark_gradient.png";
 constexpr const char* RESOURCE_LOGO = "logo_ObsidianDragon_dark.png";