async function sendMessage(e) {
    e.preventDefault();
    const input = document.getElementById('user-input');
    const chatWindow = document.getElementById('chat-window');
    const sendBtn = document.getElementById('send-btn');
    const text = input.value.trim();

    if (!text) return;

    if (inputHistory[inputHistory.length - 1] !== text) {
        inputHistory.push(text);
        if (inputHistory.length > 50) inputHistory.shift();
        localStorage.setItem(STORAGE_KEY, JSON.stringify(inputHistory));
    }
    historyIndex = -1;

    chatWindow.innerHTML += `
        <div class="flex justify-end">
            <div class="bg-indigo-600 text-white rounded-2xl px-4 py-2.5 max-w-2xl text-xs sm:text-sm shadow-sm">
                ${text}
            </div>
        </div>
    `;
    input.value = '';
    input.style.height = 'auto';
    chatWindow.scrollTop = chatWindow.scrollHeight;

    sendBtn.disabled = true;
    sendBtn.classList.add('opacity-50');

    const endpoint = IS_GUEST ? '/api/v1/chat/guest' : '/api/v1/chat';
    const headers = { 'Content-Type': 'application/json' };
    if (!IS_GUEST) {
        headers['Authorization'] = `Bearer ${API_TOKEN}`;
    }

    try {
        const res = await fetch(endpoint, {
            method: 'POST',
            headers: headers,
            body: JSON.stringify({ session_id: SESSION_ID, message: text })
        });

        if (res.status === 401 && !IS_GUEST) {
            logout();
            return;
        }

        const data = await res.json();
        const assistantTitle = IS_GUEST ? "Локальная нейросеть (Гость)" : "ИИ-Ассистент SCUD Orion AI";

        chatWindow.innerHTML += `
            <div class="bg-white border border-slate-200 rounded-2xl p-3.5 shadow-sm max-w-2xl">
                <p class="text-[11px] font-bold text-indigo-600 uppercase tracking-wider mb-1"><i class="fa-solid fa-robot mr-1"></i> ${assistantTitle}</p>
                <p class="text-slate-800 text-xs sm:text-sm whitespace-pre-wrap leading-relaxed">${data.reply}</p>
            </div>
        `;
        chatWindow.scrollTop = chatWindow.scrollHeight;
        if (!IS_GUEST) loadTasks();

    } catch (err) {
        chatWindow.innerHTML += `
            <div class="bg-red-50 border border-red-200 rounded-2xl p-3.5 max-w-2xl text-red-700 text-xs sm:text-sm">
                Ошибка связи с сервером.
            </div>
        `;
    } finally {
        sendBtn.disabled = false;
        sendBtn.classList.remove('opacity-50');
    }
}