v4.0.0: require HELLO MAJOR.MINOR lockstep before auth

1 files changed, 14 insertions, 0 deletions

diff --git a/docs/GAMES.md b/docs/GAMES.md
index bd372b1..6f6d197 100644
--- a/docs/GAMES.md
+++ b/docs/GAMES.md
@@ -182,6 +182,20 @@ database.
 
 ## Wire protocol
 
+The first line after the TLS handshake is always the version handshake:
+
+```
+HELLO <version>
+HELLO <version> latest=<version> url=<download-url>
+```
+
+Client and server must share MAJOR.MINOR; only the patch component may differ.
+Until the handshake succeeds the server answers every other message with
+`ERROR HELLO required`, and the client sends no credentials. A mismatch answers
+`ERROR Version mismatch: ...` and the client disconnects. `latest` and `url`
+drive the "newer version available" notice. The server reads `DOWNLOAD_URL`
+from its environment, falling back to the public site.
+
 Slots keeps its original exchange:
 
 ```