Key loading from files

tests/test_key_file_loading.cpp

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+// Tests for hex key file loading helpers
+#include <cassert>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+
+#include <columnlynx/common/utils.hpp>
+#include <sodium.h>
+
+int main() {
+    namespace fs = std::filesystem;
+    using namespace ColumnLynx::Utils;
+
+    fs::path tempDir = fs::temp_directory_path() / "columnlynx_key_loader_test";
+    fs::remove_all(tempDir);
+    fs::create_directories(tempDir);
+
+    auto publicKeyPath = tempDir / "public.key";
+    auto privateKeyPath = tempDir / "private.key";
+
+    {
+        std::ofstream pub(publicKeyPath);
+        pub << "00112233445566778899aabbccddeeff00112233445566778899AABBCCDDEEFF";
+    }
+
+    {
+        std::ofstream priv(privateKeyPath);
+        priv << "ffeeddccbbaa99887766554433221100ffeeddccbbaa99887766554433221100\n";
+    }
+
+    auto pk = loadHexArrayFromFile<crypto_sign_PUBLICKEYBYTES>(publicKeyPath.string(), "public key");
+    auto sk = loadHexArrayFromFile<crypto_sign_SEEDBYTES>(privateKeyPath.string(), "private key", true);
+
+    assert(pk[0] == 0x00 && pk[1] == 0x11 && pk.back() == 0xFF);
+    assert(sk[0] == 0xFF && sk[1] == 0xEE && sk.back() == 0x00);
+
+    bool threwMissing = false;
+    try {
+        (void)loadHexArrayFromFile<crypto_sign_PUBLICKEYBYTES>((tempDir / "missing.key").string(), "missing key");
+    } catch (const std::exception&) {
+        threwMissing = true;
+    }
+    assert(threwMissing && "Missing key file should throw");
+
+    auto badLengthPath = tempDir / "bad-length.key";
+    {
+        std::ofstream bad(badLengthPath);
+        bad << "abcd";
+    }
+
+    bool threwBadLength = false;
+    try {
+        (void)loadHexArrayFromFile<crypto_sign_PUBLICKEYBYTES>(badLengthPath.string(), "bad length key");
+    } catch (const std::exception&) {
+        threwBadLength = true;
+    }
+    assert(threwBadLength && "Wrong-length key file should throw");
+
+    std::cout << "Key file loader tests passed\n";
+    fs::remove_all(tempDir);
+    return 0;
+}