diff --git a/src/cli.cppm b/src/cli.cppm
index 6ca62ae..a10ecdd 100644
--- a/src/cli.cppm
+++ b/src/cli.cppm
@@ -4268,6 +4268,53 @@ int cmd_self_version(const mcpplibs::cmdline::ParsedArgs& /*parsed*/) {
     return 0;
 }
 
+int cmd_self_init(const mcpplibs::cmdline::ParsedArgs& parsed) {
+    bool force = parsed.is_flag_set("force");
+
+    if (force) {
+        // --force: delete registry (sandbox) + caches and re-bootstrap.
+        // Preserves: bin/mcpp (self-contained mode), config.toml, log/.
+        mcpp::ui::info("Resetting", "mcpp sandbox (registry, caches)");
+
+        // Resolve MCPP_HOME without running bootstrap (which may fail).
+        std::filesystem::path home;
+        if (auto* e = std::getenv("MCPP_HOME"); e && *e)
+            home = e;
+        else {
+            const char* userHome = nullptr;
+#if defined(_WIN32)
+            userHome = std::getenv("USERPROFILE");
+#endif
+            if (!userHome) userHome = std::getenv("HOME");
+            if (userHome) home = std::filesystem::path(userHome) / ".mcpp";
+        }
+        if (!home.empty()) {
+            std::error_code ec;
+            std::filesystem::remove_all(home / "registry", ec);
+            std::filesystem::remove_all(home / "bmi", ec);
+            std::filesystem::remove_all(home / "cache", ec);
+        }
+    }
+
+    // (Re-)run the full load_or_init, which does bootstrap.
+    mcpp::ui::info("Initializing", "mcpp sandbox");
+    auto cfg = mcpp::config::load_or_init();
+    if (!cfg) {
+        mcpp::ui::error(cfg.error().message);
+        return 1;
+    }
+
+    // Verify result.
+    auto problem = mcpp::config::check_base_init(*cfg);
+    if (!problem.empty()) {
+        mcpp::ui::error(std::format("init incomplete: {}", problem));
+        return 1;
+    }
+
+    mcpp::ui::status("Ready", "sandbox initialized");
+    return 0;
+}
+
 std::string upper_ascii(std::string s) {
     for (char& ch : s) {
         if (ch >= 'a' && ch <= 'z') ch = static_cast<char>(ch - 'a' + 'A');
@@ -4635,6 +4682,10 @@ int run(int argc, char** argv) {
         // ─── about mcpp itself ─────────────────────────────────────────
         .subcommand(cl::App("self")
             .description("Inspect and manage mcpp itself")
+            .subcommand(cl::App("init")
+                .description("Initialize or repair mcpp sandbox")
+                .option(cl::Option("force")
+                    .help("Delete registry and re-initialize from scratch")))
             .subcommand(cl::App("doctor")
                 .description("Diagnose mcpp environment health"))
             .subcommand(cl::App("env")
@@ -4650,11 +4701,12 @@ int run(int argc, char** argv) {
                 .arg(cl::Arg("code").help("Error code such as E0001").required()))
             .action(wrap_rc([&dispatch_sub](const cl::ParsedArgs& p) {
                 return dispatch_sub("self", p, {
-                    {"doctor",  cmd_doctor},
-                    {"env",     cmd_env},
-                    {"config",  cmd_self_config},
-                    {"version", cmd_self_version},
-                    {"explain", cmd_explain_action},
+                    {"init",      cmd_self_init},
+                    {"doctor",    cmd_doctor},
+                    {"env",       cmd_env},
+                    {"config",    cmd_self_config},
+                    {"version",   cmd_self_version},
+                    {"explain",   cmd_explain_action},
                 });
             })))
 
diff --git a/src/config.cppm b/src/config.cppm
index aa5f4b5..e3fd137 100644
--- a/src/config.cppm
+++ b/src/config.cppm
@@ -102,6 +102,61 @@ mcpp::xlings::Env make_project_xlings_env(const GlobalConfig& cfg,
     return { cfg.xlingsBinary, cfg.xlingsHome(), projectDir / ".mcpp" };
 }
 
+// Check that the sandbox bootstrap completed successfully.
+// Returns empty string if ok, or a description of what's missing.
+std::string check_base_init(const GlobalConfig& cfg) {
+    auto xlEnv = make_xlings_env(cfg);
+    struct Check { std::string_view name; std::filesystem::path path; };
+
+    auto patchelfBin = mcpp::xlings::paths::xim_tool(xlEnv, "patchelf",
+        mcpp::xlings::pinned::kPatchelfVersion) / "bin" / "patchelf";
+    auto ninjaRoot = mcpp::xlings::paths::xim_tool_root(xlEnv, "ninja");
+    auto ninja_name = std::string("ninja") + std::string(mcpp::platform::exe_suffix);
+
+    // Check xlings binary
+    if (!std::filesystem::exists(cfg.xlingsBinary))
+        return std::format("xlings binary missing: {}", cfg.xlingsBinary.string());
+
+    // Check sandbox init marker
+    auto marker = xlEnv.home / "subos" / "default" / ".xlings.json";
+    if (!std::filesystem::exists(marker))
+        return "sandbox not initialized (missing subos/default/.xlings.json)";
+
+    // Check patchelf (Linux only)
+#if !defined(__APPLE__) && !defined(_WIN32)
+    if (!std::filesystem::exists(patchelfBin))
+        return std::format("patchelf missing: {}", patchelfBin.string());
+#endif
+
+    // Check ninja
+    bool ninjaOk = false;
+    if (std::filesystem::exists(ninjaRoot)) {
+        std::error_code ec;
+        for (auto& v : std::filesystem::directory_iterator(ninjaRoot, ec)) {
+            if (std::filesystem::exists(v.path() / ninja_name)) { ninjaOk = true; break; }
+        }
+    }
+    if (!ninjaOk)
+        return "ninja missing from sandbox";
+
+    return {};  // all ok
+}
+
+// Delete the registry directory (sandbox) for a clean re-init.
+// Preserves: bin/mcpp (self-contained mode), config.toml, log/.
+void reset_registry(const GlobalConfig& cfg) {
+    std::error_code ec;
+    auto registry = cfg.xlingsHome();
+    if (std::filesystem::exists(registry))
+        std::filesystem::remove_all(registry, ec);
+
+    // Also clear BMI and metadata caches (stale after registry reset).
+    if (std::filesystem::exists(cfg.bmiCacheDir))
+        std::filesystem::remove_all(cfg.bmiCacheDir, ec);
+    if (std::filesystem::exists(cfg.metaCacheDir))
+        std::filesystem::remove_all(cfg.metaCacheDir, ec);
+}
+
 // Ensure the project-level .mcpp/ directory exists and contains a
 // .xlings.json seeded with the custom (non-builtin, non-local) index
 // entries. Returns true if a .mcpp/ directory was created/updated.
@@ -489,6 +544,16 @@ std::expected<GlobalConfig, ConfigError> load_or_init(
 #endif
     ensure_sandbox_ninja(cfg, quiet, onBootstrapProgress);
 
+    // 8. Verify bootstrap completed. If something is missing (e.g. Ctrl+C
+    //    interrupted a previous bootstrap), report the problem up-front
+    //    rather than letting a cryptic error surface later.
+    auto initProblem = check_base_init(cfg);
+    if (!initProblem.empty()) {
+        return std::unexpected(ConfigError{std::format(
+            "{}\n  hint: run `mcpp self init --force` to reset and re-initialize",
+            initProblem)});
+    }
+
     return cfg;
 }
 
diff --git a/src/xlings.cppm b/src/xlings.cppm
index 0d58e5a..b69ac8d 100644
--- a/src/xlings.cppm
+++ b/src/xlings.cppm
@@ -833,9 +833,17 @@ void ensure_init(const Env& env, bool quiet) {
 void ensure_patchelf(const Env& env, bool quiet,
                      const BootstrapProgressCallback& cb)
 {
-    auto marker = paths::xim_tool(env, "patchelf", pinned::kPatchelfVersion)
-                / "bin" / "patchelf";
-    if (std::filesystem::exists(marker)) return;
+    auto toolDir = paths::xim_tool(env, "patchelf", pinned::kPatchelfVersion);
+    auto binary  = toolDir / "bin" / "patchelf";
+    if (std::filesystem::exists(binary)) return;
+
+    // Clean up incomplete installation residue (e.g. from Ctrl+C interrupt).
+    if (std::filesystem::exists(toolDir)) {
+        if (!quiet)
+            print_status("Repairing", "patchelf (incomplete installation, cleaning up)");
+        std::error_code ec;
+        std::filesystem::remove_all(toolDir, ec);
+    }
 
     if (!quiet)
         print_status("Bootstrap", "patchelf into mcpp sandbox (one-time)");
@@ -852,12 +860,16 @@ void ensure_ninja(const Env& env, bool quiet,
                   const BootstrapProgressCallback& cb)
 {
     auto root = paths::xim_tool_root(env, "ninja");
+    auto ninja_name = std::string("ninja") + std::string(mcpp::platform::exe_suffix);
     if (std::filesystem::exists(root)) {
         std::error_code ec;
-        auto ninja_name = std::string("ninja") + std::string(mcpp::platform::exe_suffix);
         for (auto& v : std::filesystem::directory_iterator(root, ec)) {
             if (std::filesystem::exists(v.path() / ninja_name)) return;
         }
+        // Directory exists but no version has a working binary — residue.
+        if (!quiet)
+            print_status("Repairing", "ninja (incomplete installation, cleaning up)");
+        std::filesystem::remove_all(root, ec);
     }
     if (!quiet)
         print_status("Bootstrap", "ninja into mcpp sandbox (one-time)");