[Core] Predictable Instance Faction

[manstfu]

Current Behaviour

Instances created under AllowTwoSide.Interaction.Group should use the group leader's faction rather than assigning the faction based on the first player to enter. This ensures that the instance faction remains predictable and is not randomly determined by the first entrant.

Changing the raid difficulty from Normal to Heroic while leader is inside the instance correctly updates the instance faction to match the group leader's faction.

Expected Blizzlike Behaviour

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Source

No response

Steps to reproduce the problem

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Extra Notes

No response

AC rev. hash/commit

rev. b373df9+

Operating system

Debian 12

Custom changes or Modules

No response

[heyitsbench]

This does have some Blizzlike precedent to it. Karazhan's Chess event does use raid leader faction for its team selection in the case of cross-faction groups on retail, issue for that seen here. Not quite the same as the actual spawns, but it does lend some credence to this idea.

[Exitare]

@heyitsbench should that behavior be added to all dungeons and raids (classic - wotlk)