[M4] add cargoxx run/test/clean

tests/cmd_run.cpp

@@ -0,0 +1,65 @@
+#include <catch2/catch_test_macros.hpp>
+
+import cargoxx.cli;
+import cargoxx.util;
+import std;
+
+using cargoxx::cli::cmd_new;
+using cargoxx::cli::cmd_run;
+using cargoxx::util::ErrorCode;
+
+namespace {
+
+auto fresh_dir() -> std::filesystem::path {
+    auto d = std::filesystem::temp_directory_path() /
+             std::format("cargoxx-run-test-{}", std::random_device{}());
+    std::filesystem::create_directories(d);
+    return d;
+}
+
+auto overlay_path(const std::filesystem::path& dir) -> std::filesystem::path {
+    return dir / "overlay.sqlite";
+}
+
+auto add_extra_bin(const std::filesystem::path& root, std::string_view name) {
+    auto p = root / "src" / "bin" / std::format("{}.cpp", name);
+    std::filesystem::create_directories(p.parent_path());
+    std::ofstream{p} << "int main() { return 0; }\n";
+}
+
+} // namespace
+
+TEST_CASE("cmd_run errors when no binary is present", "[cli][run]") {
+    // A library-only project has no binary to run.
+    auto parent = fresh_dir();
+    REQUIRE(cmd_new("widget", true, parent).has_value());
+    auto root = parent / "widget";
+
+    auto r = cmd_run(root, false, std::nullopt, {}, overlay_path(parent));
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code == ErrorCode::LayoutNoTarget);
+}
+
+TEST_CASE("cmd_run errors when --bin doesn't match any target", "[cli][run]") {
+    auto parent = fresh_dir();
+    REQUIRE(cmd_new("app", false, parent).has_value());
+    auto root = parent / "app";
+
+    auto r = cmd_run(root, false, std::string{"missing"}, {}, overlay_path(parent));
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code == ErrorCode::LayoutNoTarget);
+}
+
+TEST_CASE("cmd_run requires --bin when multiple binaries exist", "[cli][run]") {
+    auto parent = fresh_dir();
+    REQUIRE(cmd_new("app", false, parent).has_value());
+    auto root = parent / "app";
+    add_extra_bin(root, "tool");
+
+    auto r = cmd_run(root, false, std::nullopt, {}, overlay_path(parent));
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code == ErrorCode::LayoutNoTarget);
+    // Hint should list both target names.
+    REQUIRE(r.error().hint.find("app") != std::string::npos);
+    REQUIRE(r.error().hint.find("tool") != std::string::npos);
+}