fix(rematch): move game variable from module scope to function scope

[seriouslysean]

Found during a code audit for the gpu stuff. let game is declared at module scope in the rematch controller, meaning all concurrent requests share the same variable. If two players hit rematch at the same time, the second request overwrites game while the first is still using it.

Fix is just moving the declaration inside the function.

Issue number

• N/A (found during code audit)

Please check the following

• Do the tests still pass?
• Is the code formatted properly?

Please describe additional details for testing this change

1. npm run test:unit
2. The race condition was hard to hit in practice, but this is a correctness fix — no behavior change for normal (non-concurrent) requests

[Copilot]

Pull request overview

Fixes a concurrency/race condition in the rematch controller by ensuring request-specific game state is not shared across concurrent requests.

Changes:

• Moved let game from module scope into the exported request handler scope to prevent cross-request state sharing.

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