From 625cec113b03ea7539e661f0f3b70eb626c7d5f3 Mon Sep 17 00:00:00 2001
From: Devin Zuczek <devin.zuczek@gmail.com>
Date: Fri, 2 Oct 2026 15:56:24 -0400
Subject: [PATCH] [match] on 2023 do not room switch

---
 .env.example                                |  3 ++-
 apps/match/README.md                        |  2 ++
 apps/match/src/match.app.ts                 |  7 +++++++
 apps/match/src/test/integration/api.test.ts | 21 +++++++++++++++++++--
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/.env.example b/.env.example
index 9bd74cc..e9f94c0 100644
--- a/.env.example
+++ b/.env.example
@@ -117,7 +117,8 @@ RECFLARE_DOMAIN=rec.example.com
 # it came through the room list, a club's clubhouse, or a party. Substitution is a single
 # hop (2=3,3=2 swaps the two rooms), a requested subroom is dropped in favour of the
 # substitute's default one, and a target that doesn't exist leaves the original room in
-# place. Following a friend or joining a specific instance is unaffected — those join a
+# place. Only client builds newer than 20230414 are switched; the 2023 client and older
+# enter the room they asked for. Following a friend or joining a specific instance is unaffected — those join a
 # live instance, which is already in whichever room it was created in.
 # RECFLARE_ROOM_REDIRECTS=2=MyHub
 
diff --git a/apps/match/README.md b/apps/match/README.md
index cd100f0..b1fda6c 100644
--- a/apps/match/README.md
+++ b/apps/match/README.md
@@ -112,6 +112,8 @@ substitutes the same as asking by id.
 - **One hop only** — `2=3,3=2` swaps the two rooms rather than looping.
 - **An unresolvable target leaves the original room in place** (logged), so a typo doesn't
   make a room unreachable.
+- **Only builds newer than `20230414` are substituted** — a caller on the 2023 client or
+  an older one (or on a token that names no build) enters the room they asked for.
 - **Following a friend and joining a specific instance are unaffected** — those enter a
   live instance, which is already in whichever room it was created in.
 
diff --git a/apps/match/src/match.app.ts b/apps/match/src/match.app.ts
index aed16ba..cda2b5b 100644
--- a/apps/match/src/match.app.ts
+++ b/apps/match/src/match.app.ts
@@ -1389,6 +1389,10 @@ function roomRedirects(env: Env): Map<number, string> {
  * default subroom. Substitution is a single hop — `2=3,3=2` swaps the two rooms rather
  * than looping — and an unresolvable target leaves the original room in place, so a
  * typo'd knob degrades to "no substitution" instead of a dead hub.
+ *
+ * Only builds NEWER than the 2023 client ({@link BUILD_2023}) are substituted. A caller on
+ * that build or an older one — or on a token that names none, which matchmakes as
+ * `GAME_VERSION` (see {@link callerGameVersion}) — enters the room they asked for.
  */
 async function substituteRoom(
 	c: Context<App>,
@@ -1399,6 +1403,9 @@ async function substituteRoom(
 	const to = roomRedirects(c.env).get(fromId)
 	if (to === undefined) return { room, subRoomId }
 
+	const build = buildNumber(await callerGameVersion(c))
+	if (build === null || build <= BUILD_2023) return { room, subRoomId }
+
 	const toId = Number.parseInt(to, 10)
 	const target = Number.isNaN(toId)
 		? await getRoomByName(c.env.DB, to)
diff --git a/apps/match/src/test/integration/api.test.ts b/apps/match/src/test/integration/api.test.ts
index 14ac1c7..aae058e 100644
--- a/apps/match/src/test/integration/api.test.ts
+++ b/apps/match/src/test/integration/api.test.ts
@@ -1132,12 +1132,14 @@ describe('public endpoints', () => {
 	test('ROOM_REDIRECTS switches a matchmake out to another room', async () => {
 		// `env` is shared by every test in this file, so restore the knob in `finally`.
 		const original = env.ROOM_REDIRECTS
-		const matchmake = async (path: string, player: string) =>
+		// Substitution only applies to builds newer than 20230414, so matchmake as the 2025 one
+		// unless the case says otherwise.
+		const matchmake = async (path: string, player: string, version = '20250718.01') =>
 			(await (
 				await exports.default.fetch(`${ORIGIN}${path}`, {
 					method: 'POST',
 					headers: {
-						...(await bearer(player)),
+						...(await bearer(player, version)),
 						'Content-Type': 'application/x-www-form-urlencoded',
 					},
 					// Private, so each call gets a fresh instance of whatever room it landed in.
@@ -1174,6 +1176,21 @@ describe('public endpoints', () => {
 				roomId: 77,
 			})
 
+			// The 2023 build and anything older is never substituted, nor is a token naming no
+			// build (it matchmakes as GAME_VERSION): they enter the room they asked for.
+			for (const [player, version] of [
+				['8808', '20230414'],
+				['8809', '20230414.01'],
+				['8810', '20221117'],
+			]) {
+				expect((await matchmake('/matchmake/room/2', player, version)).roomInstance).toMatchObject(
+					{ roomId: 2, name: '^RecCenter' }
+				)
+			}
+			expect((await matchmake('/matchmake/room/2', '8811', '')).roomInstance).toMatchObject({
+				roomId: 2,
+			})
+
 			// Targeting by id works the same, and substitution is a single hop: 2 and 77
 			// swap rather than bouncing between each other.
 			env.ROOM_REDIRECTS = '2=77,77=2'