[META] Online coop checklist

Existing issues from REP- discovered while working on REP+

• Isaac.Get/SetDwmWindowAttribute - Set->Get returns weird values

Known issues in REP+

• Co-op menu must be sufficiently blocked off while REPENTOGON is active (mostly done, need to block invitations, maybe other stuff?)
• Isaac.SetIcon can break if called too many times
• Decoration grids are not spawning naturally (likely related to grid entity spawn patches)

REP+ issues that might get fixed by nicalis

• https://github.com/epfly6/RepentanceAPIIssueTracker/issues/599
• https://github.com/epfly6/RepentanceAPIIssueTracker/issues/598

Things that could maybe use some more fleshed out tests

Honestly, if you feel like adding some tests for ANYTHING, especially rgon features, go for it. But in particular there were a few things I thought could be worth a look for writing tests, either due to complexity or awkwardness in actually writing tests for it.

• GenericPrompt
• Custom Item Pools
• LootList
• Ambush (weird to set up a testable state mid-test)
• EntitiesSaveState / GridEntityDesc (savestate related)
• ASM patch etc stuff if not covered yet, like ASMCallbacks/ASMXMLItem/CardsExtras

Treat this as a tracking checklist rather than a single task. Read the listed REP and REP+ items, then inspect the linked TestMod repository for the named test areas such as GenericPrompt, Custom Item Pools, LootList, and savestate coverage. Before starting, choose one item and define its affected behavior and passing test; done means that item is implemented or tested and checked off.