Pocket Links!

Every link block is one end. Two ends of the same kind on the same channel of the same pocket are one shared buffer: whatever goes in at one end comes out at the other, in whichever dimension the ends stand. Pipes, hoppers, tanks, cables and storage mods treat an end like an ordinary chest, tank or battery, so Mekanism, AE2, Pipez, Create, Thermal, Ender IO and friends connect to it like to any machine. No pipe mod at all? Set one end to pull from the chest behind it and the other to push into the chest behind it.

What you get

• Item Link: a chest-sized buffer (27 slots) shared between its ends; right-click opens it like a chest.
• Fluid Link: a 16-bucket tank; buckets and tanks-in-hand fill and empty it.
• Energy Link: a 1,000,000 FE battery.
• Nine channels per kind per pocket; more than two ends may share a channel.
• Comparators read every link. Push and pull modes move things with no pipes at all.

Controls

• Right-click, empty hand: open the buffer / show the tank or charge.
• Sneak + right-click, empty hand: next channel (1-9).
• Right-click with a wrench (any mod's) or a redstone torch: idle, push into the block behind, pull from the block behind.
• Right-click with an upgrade card: install it. Sneak + right-click with a wrench: pop the last card out.

Upgrades

Craft a blank Link Card (paper, two iron nuggets, a redstone torch) and combine it with one item:

• Speed (clock): doubles how much a push or pull moves; up to four cards (x16).
• Capacity (chest): doubles the buffer, counted across every end of the channel; up to four (27 to 432 slots, 16 to 256 buckets, 1M to 16M FE).
• Stack (piston): doubles how many items fit in one slot; up to four (64 to 1,024). Item Links only.
• Redstone (comparator): one card, the end only runs while powered; two, only while unpowered.
• Anchor (eye of ender): keeps the end's chunk loaded (server config can turn it off).
• Filter (hopper): a nine-slot whitelist or blacklist for what the end pushes and pulls. Right-click the card in the air to edit it.

Recipes

Details

• Versions: 1.21.1 and 26.2 (NeoForge, Pocket Door 1.11.0+), 1.20.1 (Forge 47, Pocket Door 1.10.0+), 1.12.2 (Forge 2860, Pocket Door 1.10.0+). Works on servers.
• Ends respect Pocket Door's rules: changing a link inside a pocket needs build rights there; visitors with use rights can open the buffer. Links don't work in the Hub.
• Buffers live with the pocket, not the block: break an end and the items wait for the next end on that channel.
• Config (pocketlinks-common.toml, pocketlinks.cfg on 1.12.2): buffer sizes, push/pull rates, outside-to-outside links, Anchor on/off, a cap on cards per end.
• Pack makers: ids pocketlinks:item_link, fluid_link, energy_link, link_card, *_upgrade; no keybinds, commands or packets; all ingredients are tags.