stcp: ed25519 pubkey exchange in handshake, fix instance destroy segfault, fix chat_tcp_test

- u_async.c: process immediate_queue BEFORE epoll_wait in uasync_poll
- stcp_link.c: defensive NULL etcp_conn/etcp_link in stcp_link_close
- utun_instance.c: move stcp_server_list_destroy_all to Phase J (before ETCP),
  add deferred drain in both Phase J and L
- stcp.h/c: STCP_HS_ENC_CLIENT 6→38, STCP_HS_ENC_SERVER 7→39,
  exchange ed25519_pubkey in both handshake directions
- etcp_connections.c: copy peer_ed25519 from STCP to ETCP_CONN in
  etcp_link_enter_ready_tcp; guard link->etcp in tcp_link_close_cb
- chat_sync.c: fix lk->conn NULL dereference for TCP links
- test_stcp.c: update stcp_server_create/stcp_client_connect callsites
- tools/chat_tcp_test: change transport udp→tcp

tools/chatgui/src/chatview.cpp

@@ -0,0 +1,191 @@
+#include "chatview.h"
+#include "messagedelegate.h"
+#include <QPainter>
+#include <QClipboard>
+#include <QApplication>
+#include <QDebug>
+#include <QMouseEvent>
+#include <QKeyEvent>
+#include <QScrollBar>
+
+ChatView::ChatView(QWidget *parent)
+    : QListView(parent)
+{
+    setMouseTracking(true);
+
+    m_scrollDownBtn = new QPushButton(QStringLiteral("\u25BC"), this);
+    m_scrollDownBtn->setFixedSize(36, 36);
+    m_scrollDownBtn->setCursor(Qt::PointingHandCursor);
+    m_scrollDownBtn->setStyleSheet(
+        "QPushButton {"
+        "  background: rgba(60,60,60,180);"
+        "  color: #ffffff;"
+        "  border: none;"
+        "  border-radius: 18px;"
+        "  font-size: 16px;"
+        "}"
+        "QPushButton:hover {"
+        "  background: rgba(90,90,90,220);"
+        "}"
+    );
+    m_scrollDownBtn->setToolTip(tr("Scroll to bottom"));
+    m_scrollDownBtn->setVisible(false);
+
+    connect(m_scrollDownBtn, &QPushButton::clicked, this, [this]() {
+        scrollToBottom();
+    });
+    connect(verticalScrollBar(), &QScrollBar::valueChanged, this, &ChatView::updateScrollDownBtn);
+    connect(verticalScrollBar(), &QScrollBar::rangeChanged, this, &ChatView::updateScrollDownBtn);
+
+    m_scrollDownBtn->raise();
+}
+
+void ChatView::setBackgroundImage(const QString &path) {
+    if (!m_background.load(path)) {
+        qWarning() << "ChatView: failed to load background" << path;
+        return;
+    }
+    viewport()->update();
+}
+
+void ChatView::resizeEvent(QResizeEvent *event) {
+    QListView::resizeEvent(event);
+    scheduleDelayedItemsLayout();
+    updateScrollDownBtn();
+}
+
+void ChatView::scrollContentsBy(int dx, int dy) {
+    QListView::scrollContentsBy(dx, dy);
+    viewport()->update();
+}
+
+void ChatView::paintEvent(QPaintEvent *event) {
+    if (!m_background.isNull()) {
+        QPainter p(viewport());
+        p.drawTiledPixmap(viewport()->rect(), m_background);
+    }
+    QListView::paintEvent(event);
+}
+
+bool ChatView::isRowSelected(const QModelIndex &idx) const {
+    if (!m_selStart.isValid() || !m_selEnd.isValid() || !idx.isValid())
+        return false;
+    int r = idx.row();
+    int a = m_selStart.row();
+    int b = m_selEnd.row();
+    if (a > b) qSwap(a, b);
+    return r >= a && r <= b;
+}
+
+void ChatView::mousePressEvent(QMouseEvent *event) {
+    if (event->button() != Qt::LeftButton) {
+        QListView::mousePressEvent(event);
+        return;
+    }
+    if (hasSelection()) {
+        m_selStart = QPersistentModelIndex();
+        m_selEnd   = QPersistentModelIndex();
+        m_textSel  = ChatTextSelection{};
+        m_selecting = false;
+        viewport()->update();
+    }
+    QModelIndex idx = indexAt(viewport()->mapFrom(this, event->pos()));
+    m_pressIndex = QPersistentModelIndex(idx);
+    m_pressPos = event->pos();
+    QListView::mousePressEvent(event);
+}
+
+void ChatView::mouseMoveEvent(QMouseEvent *event) {
+    if (!m_selecting && m_pressIndex.isValid()) {
+        int dx = event->pos().x() - m_pressPos.x();
+        int dy = event->pos().y() - m_pressPos.y();
+        if (dx * dx + dy * dy >= 25) {
+            m_selStart = m_pressIndex;
+            m_selEnd   = m_pressIndex;
+            m_selecting = true;
+            QRect r = visualRect(QModelIndex(m_pressIndex));
+            m_textSel.index    = m_pressIndex;
+            m_textSel.clickPos = m_pressPos - r.topLeft();
+            m_textSel.dragPos  = m_textSel.clickPos;
+            m_textSel.active   = true;
+            viewport()->update();
+        }
+    }
+    if (!m_selecting) {
+        QModelIndex idx = indexAt(viewport()->mapFrom(this, event->pos()));
+        if (idx != QModelIndex(m_lastHovered)) {
+            m_lastHovered = idx;
+            emit hoveredIndexChanged(idx);
+        }
+    }
+    if (!m_selecting) {
+        QListView::mouseMoveEvent(event);
+        return;
+    }
+    QModelIndex idx = indexAt(viewport()->mapFrom(this, event->pos()));
+    if (idx.isValid()) {
+        m_selEnd = idx;
+    }
+    if (m_textSel.active) {
+        QRect r = visualRect(QModelIndex(m_textSel.index));
+        m_textSel.dragPos = event->pos() - r.topLeft();
+    }
+    viewport()->update();
+    event->accept();
+}
+
+void ChatView::mouseReleaseEvent(QMouseEvent *event) {
+    if (event->button() == Qt::LeftButton && m_selecting) {
+        m_selecting = false;
+        viewport()->update();
+    }
+    m_pressIndex = QPersistentModelIndex();
+    QListView::mouseReleaseEvent(event);
+}
+
+void ChatView::keyPressEvent(QKeyEvent *event) {
+    if (event == QKeySequence::Copy) {
+        copySelection();
+        return;
+    }
+    QListView::keyPressEvent(event);
+}
+
+void ChatView::copySelection() {
+    if (!hasSelection()) return;
+    auto *m = model();
+    if (!m) return;
+
+    if (selStart() == selEnd()) {
+        QModelIndex idx(selStart());
+        QString text = idx.data(MsgTextRole).toString();
+        if (m_textSel.startChar >= 0 && m_textSel.endChar > m_textSel.startChar)
+            text = text.mid(m_textSel.startChar, m_textSel.endChar - m_textSel.startChar);
+        QApplication::clipboard()->clear(QClipboard::Clipboard);
+        QApplication::clipboard()->setText(text);
+    } else {
+        QString r;
+        int a = selStart().row(), b = selEnd().row();
+        if (a > b) qSwap(a, b);
+        for (int i = a; i <= b; ++i) {
+            QModelIndex idx = m->index(i, 0);
+            if (!r.isEmpty()) r += '\n';
+            r += '[' + idx.data(MsgTimeRole).toString() + "] ";
+            r += idx.data(MsgAuthorRole).toString() + ": ";
+            r += idx.data(MsgTextRole).toString();
+        }
+        QApplication::clipboard()->clear(QClipboard::Clipboard);
+        QApplication::clipboard()->setText(r);
+    }
+}
+
+void ChatView::updateScrollDownBtn() {
+    QScrollBar* sb = verticalScrollBar();
+    bool atBottom = sb && (sb->value() >= sb->maximum());
+    m_scrollDownBtn->setVisible(!atBottom);
+    if (!atBottom) {
+        QRect vr = viewport()->geometry();
+        m_scrollDownBtn->move(vr.right() - 44, vr.bottom() - 44);
+        m_scrollDownBtn->raise();
+    }
+}