[match] support a cluster of tachyon servers

.env.example

@@ -108,12 +108,21 @@ RECFLARE_DOMAIN=rec.example.com
 # RECFLARE_PHOTON_VOICE_APP_ID=
 # RECFLARE_PHOTON_CHAT_APP_ID=
 
-# The Tachyon voice server (`match`, GET /player/connection-info): the `host:port` the
-# client is handed as `voiceConnectionInfo`, and its id as `voiceServerId`. EMPTY unless
-# you set them — no separate voice server. Set both or neither; like the Photon ids they
-# are not secrets (the client receives them in the clear).
+# The pool of Tachyon servers sessions are spread across (`match`, GET
+# /player/connection-info): a COMMA-SEPARATED list of `host:port` entries, one of which
+# the client is handed as `voiceConnectionInfo`. EMPTY unless you set it — no separate
+# voice server. Not a secret (the client receives the address in the clear), like the
+# Photon ids above. One entry is the ordinary single-server case:
 # RECFLARE_TACHYON_HOST_PORT=127.0.0.1:7777
-# RECFLARE_TACHYON_NAME=server-1
+#
+# List several and each room instance is assigned one for its lifetime, so everybody in
+# a session lands on the same server while different sessions spread across the pool.
+# The id the client displays (`voiceServerId`) is generated from an entry's POSITION —
+# `tachyon-1`, `tachyon-2`, … — so listing one address twice models two server slots on
+# one box, and inserting an entry renames every server after it. The five below are a
+# mock pool (RFC 5737 documentation addresses, which answer nothing): tachyon-1/-2 share
+# a host, as do tachyon-4/-5.
+# RECFLARE_TACHYON_HOST_PORT=198.51.100.10:7777,198.51.100.10:7778,198.51.100.11:7777,203.0.113.20:7777,203.0.113.20:7778
 
 # The Photon region every session is pinned to (`match`). Unlike the app ids above this
 # does default, to `us` (us-east1) — an instance stamped with an empty region is one the