Swamp Key Persist

Makes the Swamp Key / Crypt Key ($item_cryptkey) persist indefinitely instead of being consumed one-per-use when opening a Sunken Crypt gate.

Why this exists

In vanilla Valheim the Crypt Key is not consumed — you keep it forever. Some mods change this by hooking Door.Open and removing one key from your inventory every time you open a Sunken Crypt gate (with no config option to turn it off). This mod counters that behavior so your key behaves like vanilla again: open as many crypts as you like, the key stays.

How it works

Patch-order-proof and mod-agnostic. A Door.Open Prefix opens a short "protect window" and records the door's key item name; a Finalizer closes it. Because Harmony finalizers run after every postfix, the window reliably spans any other mod's Door.Open postfix regardless of patch order. While the window is open, prefixes on Inventory.RemoveOneItem / RemoveItem refuse to delete that key (and report success, so the other mod's logic is unaffected).

It only protects the key during a crypt-gate open — you can still drop, store, trade, or craft with the key normally.

Anti-cheat: server-sanctioned

The key consume is a client-side operation, so on its own this DLL could be carried to any server to keep keys. To prevent that, key protection only activates on a server that also runs this mod (or when you are the host). A sanctioning server sends each connecting client a tiny ServerHello handshake RPC; a client only protects keys once it has received that Hello. On a server that does not run the mod, no Hello arrives, protection stays off, and keys consume normally. The gate is hardcoded (not exposed in config) so it can't be flipped off to cheat elsewhere.

Installation

This is a client + server mod. The server must run it to sanction key-persistence, and each player must also install it (the consume happens on the client). Install on both with a mod manager, or manually drop SwampKeyPersist.dll into BepInEx/plugins.

Configuration

baka.SwampKeyPersist.cfg:

Verifying it works

After opening a Sunken Crypt gate, the BepInEx console logs:

Preserved door key '$item_cryptkey' (blocked consume on crypt-gate open).