fix: preserve authentication transcript order

Defer RSA, ECDH, and handshake completion until after each received packet
has been added to the authentication transcript, matching the upstream
workqueue ordering and preventing the controller from rejecting host secret.

Co-Authored-By: openai/gpt-5.6-luna: fixed GIP authentication ordering

src/auth/auth.cpp

@@ -367,9 +367,30 @@ auto auth::handle_pkt_data(std::span<u8 const> data) -> int
         return err;
 
     transcript_.update(data.subspan(sizeof(hdr->handshake)));
+    run_deferred_action();
     return 0;
 }
 
+auto auth::run_deferred_action() -> void
+{
+    auto action = deferred_action_;
+    deferred_action_ = deferred_action::none;
+
+    switch (action) {
+    case deferred_action::exchange_rsa:
+        exchange_rsa();
+        break;
+    case deferred_action::exchange_ecdh:
+        exchange_ecdh();
+        break;
+    case deferred_action::complete:
+        complete_handshake();
+        break;
+    case deferred_action::none:
+        break;
+    }
+}
+
 auto auth::dispatch_pkt(u8 cmd, std::span<u8 const> data) -> int
 {
     switch (cmd) {
@@ -420,7 +441,7 @@ auto auth::handle_certificate(std::span<u8 const> data) -> int
             return -EINVAL;
 
         std::memcpy(pubkey_client_.data(), data.data() + i, k_pubkey_len);
-        exchange_rsa();
+        deferred_action_ = deferred_action::exchange_rsa;
         return 0;
     }
 
@@ -443,7 +464,7 @@ auto auth::handle_finish(std::span<u8 const> data) -> int
         return -EPROTO;
     }
 
-    complete_handshake();
+    deferred_action_ = deferred_action::complete;
     return 0;
 }
 
@@ -488,7 +509,7 @@ auto auth::handle_pubkey(std::span<u8 const> data) -> int
         return -EINVAL;
 
     std::memcpy(pubkey_client2_.data(), pkt->pubkey.data(), k_pubkey2_len);
-    exchange_ecdh();
+    deferred_action_ = deferred_action::exchange_ecdh;
     return 0;
 }