debug: trace GIP authentication headers

Log incoming and outgoing authentication context, command, option, and
length fields to isolate the handshake failure before input reports begin.

Co-Authored-By: openai/gpt-5.6-luna: added authentication diagnostics

src/auth/auth.cpp

@@ -157,6 +157,12 @@ auto auth::process_pkt(std::span<u8 const> data) -> int
     if (data.size() < sizeof(*hdr))
         return -EINVAL;
 
+    log_msg(log_level::debug,
+            "auth: rx context=0x%02x options=0x%02x error=0x%02x "
+            "command=0x%02x length=%u",
+            hdr->context, hdr->options, hdr->error, hdr->command,
+            load_be16(&hdr->length));
+
     if (hdr->error)
         return -EPROTO;
 
@@ -187,6 +193,9 @@ auto auth::send_pkt(u8 cmd, void const* pkt, std::size_t len) -> int
     store_be16(&hdr->data.length, static_cast<u16>(data_len - sizeof(hdr->data)));
 
     last_sent_command_ = cmd;
+    log_msg(log_level::debug,
+            "auth: tx command=0x%02x data_length=%u acknowledge=1",
+            cmd, data_len);
     transcript_.update(
         {reinterpret_cast<u8 const*>(hdr) + sizeof(hdr->handshake), data_len});
 
@@ -204,6 +213,9 @@ auto auth::request_pkt(u8 cmd, std::uint16_t len) -> int
     req.header.command = cmd;
     store_be16(&req.header.length, data_len);
 
+    log_msg(log_level::debug,
+            "auth: tx request command=0x%02x data_length=%u acknowledge=1",
+            cmd, data_len);
     return sink_.send({reinterpret_cast<u8 const*>(&req), sizeof(req)}, true);
 }