Eliminate timer races and stale callbacks across game session lifecycle

[llinsss]

Problem

Answer processing spans unmanaged timeouts in both QuestionCard and the game modes. A challenge can expire during the 600 ms answer delay, yet the callback captured before expiry can still record the result and grant rewards. Rapid navigation/restart can also leave 400/800 ms callbacks alive, allowing stale sessions to mutate the new session or update an unmounted component.

Proposed scope

• Model question/session lifecycle explicitly (idle, answering, feedback, complete).
• Make result recording idempotent per question/session.
• Cancel all pending timers on question change, restart, expiry, and unmount.
• At commit time, verify the current session token and deadline rather than relying on stale React closures.
• Decide whether an answer selected before zero but committed after zero counts, and encode that rule consistently.

Acceptance criteria

• No score, reward, progress, badge, speech, or question mutation occurs after session completion/unmount.
• One question can produce at most one result even under double clicks and timer races.
• Restarted sessions cannot receive callbacks from the previous session.
• The score screen totals remain stable after appearing.
• Fake-timer tests cover expiry during feedback, restart during feedback, navigation, and rapid input.

[caramel222]

hi, can i work on this?

[grantfox-oss]

🦊 GrantFox — @caramel222 has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #6)
2. Your PR will be reviewed by the DogStark maintainers

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