[faceofcat]

What this is

A small fix to how the client predicts clicks in machine menus, and the first step towards the reservations design on #83. It has no reservations in it and doesn't need the processor.

The problem. The client's MachineMenu backs its slots with a blank new ItemStackHandler(count), which accepts anything up to a full stack. From the code, it predicts placing items in output slots, past slot limits and against filters, and the server then corrects it. I haven't watched that flicker happen in a running game.

The fix. ClientMenuItems is the new client handler:

• Contents still come from vanilla's menu sync, in the handler's own stacks.
• Rules (isItemValid, getSlotLimit) come from the client block entity's own screenItems(), which has the same roles, filters and limits on any ScreenHost. Its contents aren't read or changed.
• Ghost slots can take the menu's slot count past the end of the storage. Those indexes are refused rather than thrown, since no real slot uses them.

The server still decides. A filter that depends on server-only state can still mispredict, and the server corrects it as it does today.

Review notes

• New requirement: screenItems() must now work on the client. ScreenHost and docs/gui-screens.md say so. The default screenDestinations already relied on it, but a host that overrides that and has no client storage would now fail when the menu asks about a slot.
• Test machine: Counter gets an output slot, a filter and a limit, because it had none, so the GUI smoke test can check them.
• Separate from Move the builder checks to JUnit #84: nothing here depends on it, and the two don't touch the same files, apart from both being based on the merged Machine recipe types: datapack loading, lookup, datagen and JEI #83.

Testing

• ./gradlew check passes locally, including all 19 game tests. clientMenuItems is new and checks the handler against a real ItemStorage.
• The GUI smoke test now checks a real client menu: the input slot's limit and filter, and that an output slot refuses a placement.
• I didn't run the GUI smoke test locally, so the CI job on this PR is its only run, and I haven't seen those client checks fail against the old handler.

🤖 Generated with Claude Code

[dshadowwolf]

No comments -- waiting on CI, this is an excellent PR