[fix] restore password prompts and handle join authentication failures

apps/desktop/src/gui/runtime/connection_auth_state.h

@@ -0,0 +1,72 @@
+#ifndef CROSSDESK_CONNECTION_AUTH_STATE_H_
+#define CROSSDESK_CONNECTION_AUTH_STATE_H_
+
+#include <chrono>
+#include <mutex>
+#include <string_view>
+
+#include "join_failure.h"
+
+namespace crossdesk {
+
+// One remote session's password prompt and server-requested retry delay.
+// Signaling callbacks and the UI access a single synchronized snapshot.
+class ConnectionAuthState {
+ public:
+  using Clock = std::chrono::steady_clock;
+  struct Snapshot {
+    bool password_required = false;
+    bool validating = false;
+    bool incorrect_password = false;
+    minirtc::JoinFailureKind error = minirtc::JoinFailureKind::Unknown;
+    int retry_after = 0;
+  };
+
+  bool Begin(std::string_view password, Clock::time_point now = Clock::now()) {
+    std::lock_guard lock(mutex_);
+    if (retry_at_ > now) return false;
+    state_ = {};
+    retry_at_ = {};
+    state_.password_required = password.empty();
+    state_.validating = !password.empty();
+    return state_.validating;
+  }
+
+  void Rejected(const nlohmann::json& reply,
+                Clock::time_point now = Clock::now()) {
+    const auto failure = minirtc::ParseJoinFailure(reply);
+    std::lock_guard lock(mutex_);
+    state_ = {};
+    state_.error = failure.kind;
+    state_.incorrect_password =
+        failure.kind == minirtc::JoinFailureKind::AuthenticationFailed;
+    state_.password_required =
+        state_.incorrect_password ||
+        failure.kind == minirtc::JoinFailureKind::PasswordRequired;
+    retry_at_ = now + std::chrono::seconds(failure.retry_after);
+  }
+
+  void Complete() {
+    std::lock_guard lock(mutex_);
+    state_.validating = false;
+  }
+
+  Snapshot Get(Clock::time_point now = Clock::now()) const {
+    std::lock_guard lock(mutex_);
+    auto snapshot = state_;
+    if (retry_at_ > now) {
+      snapshot.retry_after = static_cast<int>(
+          std::chrono::ceil<std::chrono::seconds>(retry_at_ - now).count());
+    }
+    return snapshot;
+  }
+
+ private:
+  mutable std::mutex mutex_;
+  Snapshot state_;
+  Clock::time_point retry_at_{};
+};
+
+}  // namespace crossdesk
+
+#endif