[DeckShare] Open shared decks via links with a gated preview flow

- Serialized url-chain dispatcher in IntentUrlParser; queue-drained
  urlChainFinished(bool) drives the startup auto-connect fallback
- Open-shared-deck intent with sequential download state machine,
  15s per-item timeout, partial-success offer, livable Cancel via
  ApplicationModal dlg_login_prompt interactive fallback
- Preview dialog: download progress label, share vocab sweep,
  palette-highlight selection frame, Space/Enter keyboard toggle,
  NoFocus checkbox, double-click tile opens immediately
- Confirm-before-server-migration with one-shot restore to the
  previous server on failed/cancelled chains (statusChanged settle
  deferral), hostname-only identity comparisons
- Skip credential link when already connected; arrow-key navigation
  in FlowWidget; card glows use palette highlight
- Address code-review M1-M4 and UI/UX QA blockers 1-2

cockatrice/src/interface/intents/intent_open_shared_deck.cpp

@@ -0,0 +1,190 @@
+#include "intent_open_shared_deck.h"
+
+#include "../deck_loader/deck_loader.h"
+#include "../widgets/dialogs/dlg_shared_decks_preview.h"
+#include "../widgets/tabs/tab_supervisor.h"
+#include "intent_connect_to_server.h"
+
+#include <QMessageBox>
+#include <QTimer>
+#include <libcockatrice/card/database/card_database_querier.h>
+#include <libcockatrice/protocol/pb/command_deck_share_download.pb.h>
+#include <libcockatrice/protocol/pb/command_deck_share_list.pb.h>
+#include <libcockatrice/protocol/pb/response.pb.h>
+#include <libcockatrice/protocol/pb/response_deck_share_download.pb.h>
+#include <libcockatrice/protocol/pb/response_deck_share_list.pb.h>
+#include <libcockatrice/protocol/pb/serverinfo_deck_share_item.pb.h>
+#include <libcockatrice/protocol/pending_command.h>
+
+IntentOpenSharedDeck::IntentOpenSharedDeck(TabSupervisor *_tabSupervisor,
+                                           RemoteClient *_remoteClient,
+                                           const CardDatabaseQuerier *_querier,
+                                           std::unique_ptr<ContextOpenDeck> _context)
+    : Intent(), tabSupervisor(_tabSupervisor), remoteClient(_remoteClient), querier(_querier),
+      context(_context.release())
+{
+    downloadTimer = new QTimer(this);
+    downloadTimer->setSingleShot(true);
+    downloadTimer->setInterval(15000);
+    connect(downloadTimer, &QTimer::timeout, this, &IntentOpenSharedDeck::onDownloadTimeout);
+}
+
+bool IntentOpenSharedDeck::checkPrecondition() const
+{
+    if (remoteClient->getStatus() != ClientStatus::StatusLoggedIn) {
+        return false;
+    }
+    // serverName() reflects the server the client was configured to connect to,
+    // which may differ from the actual TCP peer (e.g. when connecting through a
+    // proxy), so only the hostname is compared here.
+    return remoteClient->serverName().compare(context->serverContext.hostname, Qt::CaseInsensitive) == 0;
+}
+
+void IntentOpenSharedDeck::onPreconditionSatisfied()
+{
+    // Resolve the share token to its items first; a share can contain more than
+    // one deck, and each item is downloaded by id.
+    Command_DeckShareList cmd;
+    cmd.set_token(context->shareToken.toStdString());
+
+    PendingCommand *pend = AbstractClient::prepareSessionCommand(cmd);
+    connect(pend, &PendingCommand::finished, this, &IntentOpenSharedDeck::listShareFinished);
+    remoteClient->sendCommand(pend);
+}
+
+void IntentOpenSharedDeck::onPreconditionNotSatisfied()
+{
+    runDependency(new IntentConnectToServer(remoteClient, &context->serverContext));
+}
+
+void IntentOpenSharedDeck::listShareFinished(const Response &response, const CommandContainer & /* commandContainer */)
+{
+    if (response.response_code() != Response::RespOk) {
+        emitFailed(tr("The shared deck could not be found or has expired"));
+        return;
+    }
+
+    const Response_DeckShareList &resp = response.GetExtension(Response_DeckShareList::ext);
+    if (resp.items_size() == 0) {
+        emitFailed(tr("The shared deck is empty"));
+        return;
+    }
+
+    QList<ServerInfo_DeckShareItem> items;
+    items.reserve(resp.items_size());
+    for (const ServerInfo_DeckShareItem &item : resp.items()) {
+        items.append(item);
+        itemNames.insert(item.id(), QString::fromStdString(item.name()));
+    }
+
+    const QString serverText = context->serverContext.hostname + ":" + context->serverContext.port;
+
+    // Ask the user which decks to open before downloading anything.
+    previewDialog = new DlgSharedDecksPreview(tabSupervisor, querier, QString::fromStdString(resp.name()),
+                                              resp.expires_at(), serverText, items);
+    connect(previewDialog, &DlgSharedDecksPreview::openRequested, this, &IntentOpenSharedDeck::startDownloads);
+    connect(previewDialog, &DlgSharedDecksPreview::cancelled, this, &IntentOpenSharedDeck::emitCancelled);
+    connect(previewDialog, &DlgSharedDecksPreview::cancelled, previewDialog, &QWidget::deleteLater);
+    previewDialog->show();
+    previewDialog->raise();
+    previewDialog->activateWindow();
+}
+
+void IntentOpenSharedDeck::startDownloads(const QList<int> &itemIds)
+{
+    pendingItemIds = itemIds;
+    totalItems = itemIds.size();
+    completedItems = 0;
+    loadedDecks.clear();
+    downloadNextItem();
+}
+
+void IntentOpenSharedDeck::downloadNextItem()
+{
+    if (pendingItemIds.isEmpty()) {
+        finishAll();
+        return;
+    }
+
+    currentItemId = pendingItemIds.takeFirst();
+    downloadTimer->start();
+
+    Command_DeckShareDownload cmd;
+    cmd.set_token(context->shareToken.toStdString());
+    cmd.set_item_id(currentItemId);
+
+    PendingCommand *pend = AbstractClient::prepareSessionCommand(cmd);
+    connect(pend, &PendingCommand::finished, this, &IntentOpenSharedDeck::downloadShareFinished);
+    remoteClient->sendCommand(pend);
+}
+
+void IntentOpenSharedDeck::downloadShareFinished(const Response &response,
+                                                 const CommandContainer & /* commandContainer */)
+{
+    downloadTimer->stop();
+
+    QString failureReason;
+    if (response.response_code() != Response::RespOk) {
+        failureReason = tr("Failed to download the shared deck");
+    } else {
+        const Response_DeckShareDownload &resp = response.GetExtension(Response_DeckShareDownload::ext);
+        const QString deckString = QString::fromStdString(resp.deck());
+        if (deckString.isEmpty()) {
+            failureReason = tr("The shared deck is empty");
+        } else {
+            std::optional<LoadedDeck> deckOpt =
+                DeckLoader::loadFromRemote(deckString, LoadedDeck::LoadInfo::NON_REMOTE_ID);
+            if (!deckOpt) {
+                failureReason = tr("The shared deck could not be loaded");
+            } else {
+                loadedDecks.append(deckOpt.value());
+                ++completedItems;
+                previewDialog->setDownloadProgress(completedItems, totalItems,
+                                                   itemNames.value(currentItemId, tr("Unknown deck")));
+                downloadNextItem();
+                return;
+            }
+        }
+    }
+
+    onItemFailure(failureReason);
+}
+
+void IntentOpenSharedDeck::onItemFailure(const QString &reason)
+{
+    downloadTimer->stop();
+
+    if (loadedDecks.isEmpty()) {
+        previewDialog->deleteLater();
+        emitFailed(reason);
+        return;
+    }
+
+    const int downloadedCount = loadedDecks.size();
+    const QMessageBox::StandardButton answer = QMessageBox::question(
+        previewDialog, tr("Open shared decks"),
+        tr("Could not download the deck \"%1\".\n\n%n deck(s) were already downloaded. Open them?", "", downloadedCount)
+            .arg(itemNames.value(currentItemId, tr("Unknown deck"))),
+        QMessageBox::Yes | QMessageBox::No, QMessageBox::Yes);
+
+    if (answer == QMessageBox::Yes) {
+        finishAll();
+    } else {
+        previewDialog->deleteLater();
+        emitCancelled();
+    }
+}
+
+void IntentOpenSharedDeck::onDownloadTimeout()
+{
+    onItemFailure(tr("Timed out while downloading the shared deck"));
+}
+
+void IntentOpenSharedDeck::finishAll()
+{
+    previewDialog->deleteLater();
+    for (const LoadedDeck &deck : loadedDecks) {
+        tabSupervisor->openDeckInNewTab(deck);
+    }
+    emitFinished();
+}