Game Center matchmaking fails for all non-default users on Apple TV — no IDS registration for secondary users (FB24156316)

Game Center matchmaking fails for all non-default users on Apple TV — no IDS registration for secondary users (FB24156316)

On a multi-user Apple TV (tvOS 26.5, Apple TV 4K 3rd gen), Game Center real-time matchmaking fails for every user except the default user, in every app I've tested — including Apple Arcade titles. Filed as FB24156316 with full logs and sysdiagnose; posting here for visibility and in case anyone has shipped multi-user GC multiplayer on tvOS successfully.

My game adopts com.apple.developer.user-management (runs-as-current-user-with-user-independent-keychain). The entitlement itself works: on a secondary user's profile the app runs under that user's persona and GKLocalPlayer authenticates as them — the welcome banner shows the right account. But any GKMatchmakerViewController quickmatch hard-fails within ~9 seconds ("Failed to find players"), and accepting an invite fails with GKError 35 ("not signed in to iCloud") even though Settings shows that user's iCloud as signed in.

Unified logs show the root cause. When matchmaking starts, gamed can't provision the player's pseudonym because the current user has no identity-services registration:

gamed  No URI found on any account -- returning nil
gamed  Failed to fetch pseudonym for local player. Error:
       GameDaemonCore.PseudonymManagerError.failedToProvision(
         internalError: Error Domain=com.apple.ids.IDSPseudonymErrorDomain
         Code=400 "Invalid URI")

For the default user, the identical flow succeeds (identityservicesd … resultCode: 0). Across a full day of log capture — profile adds, a remove/re-add, multiple user switches — identityservicesd never once references the secondary users' accounts: registration for them is never attempted, not attempted-and-failed. Meanwhile gamed advertises the nearby-matchmaking Bonjour service with the default user's identity while the foreground app runs as the secondary user.

Reproduction matrix: two apps (my shipping game Extreme Violence and Apple Arcade's Crossy Road Castle, which also runs under the correct persona), both sandbox and production Game Center, two unrelated secondary accounts (both healthy elsewhere). Persists across reboot and profile remove/re-add. Default user unaffected.

The documentation says the entitlement is all that's needed ("each person who uses your app will have access to… their own Game Center… you don't have to make any code changes" — WWDC20 session 10645). As far as I can tell that promise is currently unfulfillable for online play: there is no API or Settings path that creates the missing IDS registration.

Has anyone seen non-default-user matchmaking work on tvOS, on any version? Is there anything an app can do here, or is this purely an OS-side fix? (Related: thread 782163 — a different tvOS matchmaking failure that DTS confirmed as a bug.)