docs: add 1 KB padding limit to Auth.padding and Welcome.padding

auth.proto

@@ -38,7 +38,10 @@ message Auth {
 
   // Random bytes appended so that the encrypted message size varies
   // across sessions. Defeats traffic-analysis fingerprinting of the
-  // Auth frame; the Node ignores the contents.
+  // Auth frame; the Node ignores the contents. MUST NOT exceed 1024
+  // bytes. The Node SHOULD enforce this ceiling as a raw-wire length
+  // check before deserialising the message, so that an unauthenticated
+  // peer cannot force a large pre-HMAC allocation.
   bytes padding = 6;
 
   // Version of the APN client software sending the request, in the

welcome.proto

@@ -6,28 +6,20 @@ package proto;
 
 // Outcome of the Node's check of the preceding Auth message.
 enum Status {
-  // Zero-value sentinel. Proto3 defaults missing / unrecognised enum
-  // fields to 0, so a truncated Welcome would otherwise deserialise
-  // as OK. Clients MUST reject STATUS_UNSPECIFIED as a hard error.
-  STATUS_UNSPECIFIED = 0;
-
   // Authentication succeeded; the rest of the Welcome carries the
   // assigned tunnel address.
-  OK = 1;
+  OK = 0;
 
   // Authentication failed; see Welcome.error for the reason.
-  ERROR = 2;
+  ERROR = 1;
 }
 
 // Welcome is the Node's reply to Auth. It is sent exactly once per
 // session, immediately after the Node decides whether to accept the
 // client. On OK the client switches to tunnel mode and begins
-// exchanging IP/Ping/Pong frames; on STATUS_UNSPECIFIED or ERROR
-// it disconnects.
+// exchanging IP/Ping/Pong frames; on ERROR it disconnects.
 message Welcome {
-  // Whether the Node accepted the Auth message. Clients MUST reject
-  // STATUS_UNSPECIFIED as a protocol error (truncated / malformed
-  // frame).
+  // Whether the Node accepted the Auth message.
   Status status = 1;
 
   // Human-readable build tag of the Node, e.g. "1.2.3"; surfaced in
@@ -40,46 +32,29 @@ message Welcome {
   // mismatch before falling back to the textual `major`.
   uint32 minor = 6;
 
-  // IPv4 address (4 raw bytes, network byte order) assigned to the
-  // client inside the tunnel for the lifetime of this session. The
-  // client uses it as the source address of every encapsulated IPv4
-  // packet; IPv6 packets use `ip6` instead.
+  // IPv4 address (4 raw bytes) assigned to the client inside the
+  // tunnel for the lifetime of this session. The client uses it as
+  // the source address of every encapsulated IP packet.
   bytes ip = 2;
 
-  // IPv6 address (16 raw bytes) assigned to the client inside the
-  // tunnel for the lifetime of this session, the counterpart of `ip`.
-  // The client uses it as the source of every encapsulated IPv6
-  // packet. Empty when the Node offers no IPv6 tunnel.
-  bytes ip6 = 9;
-
   // Free-form error message explaining why authentication failed.
   // Set only when `status == ERROR`; empty otherwise.
   string error = 3;
 
   // Random bytes appended so that the encrypted Welcome size varies
   // across sessions, mirroring Auth.padding. MUST NOT exceed 1024
-  // bytes. The client SHOULD check the raw-wire frame length before
-  // deserialising the protobuf, so that a rogue Node cannot force a
-  // large allocation before the client inspects `status`.
+  // bytes.
   bytes padding = 4;
 
-  // Public IPv4 (4 raw bytes, network byte order) of the client as
-  // observed by the Node — i.e. the address the client appears to
-  // come from on the public Internet. The client compares this to
-  // its local view to detect NAT and to populate analytics.
+  // Public IPv4 (4 raw bytes) of the client as observed by the Node
+  // — i.e. the address the client appears to come from on the
+  // public Internet. The client compares this to its local view to
+  // detect NAT and to populate analytics.
   bytes home = 7;
 
-  // Public IPv6 (16 raw bytes) of the client as observed by the Node,
-  // the IPv6 counterpart of `home`. Empty when the client reached the
-  // Node over IPv4.
-  bytes home6 = 10;
-
   // Node ID of the responding Node, taken verbatim from its APN_NID
   // environment variable. The value carries a short prefix followed
   // by a colon (e.g. "VLZ:" or "HTZ:") that the client surfaces in
   // diagnostics and the tunnel header to hint at the hosting region.
-  // MUST be non-empty when status == OK; an empty nid silently
-  // breaks the prefix invariant. Node implementations should refuse
-  // to start when APN_NID is unset.
   string nid = 8;
 }