Add API to give devices a reference to their context, to flag stuff as dirty e.g.

src/main/java/li/cil/oc2/api/bus/BlockDeviceBusElement.java

@@ -3,7 +3,7 @@
 package li.cil.oc2.api.bus;
 
 import net.minecraft.core.BlockPos;
-import net.minecraft.world.level.LevelAccessor;
+import net.minecraft.world.level.Level;
 
 import javax.annotation.Nullable;
 
@@ -21,7 +21,7 @@ public interface BlockDeviceBusElement extends DeviceBusElement {
      * @return the level the bus lives in.
      */
     @Nullable
-    LevelAccessor getLevel();
+    Level getLevel();
 
     /**
      * The position of this bus element.

src/main/java/li/cil/oc2/api/bus/device/Device.java

@@ -8,6 +8,8 @@ import net.minecraft.nbt.CompoundTag;
 import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraftforge.common.util.INBTSerializable;
 
+import javax.annotation.Nullable;
+
 /**
  * Base interface for objects that can be registered as devices on a {@link DeviceBus}.
  * <p>
@@ -21,11 +23,39 @@ import net.minecraftforge.common.util.INBTSerializable;
  * detected.
  */
 public interface Device extends INBTSerializable<CompoundTag> {
+    /**
+     * Called when the device is picked up by a {@link DeviceContainer}.
+     * <p>
+     * This only means the device will be hosted by the specified container, it has no implication
+     * on whether the device is actually used by a computer, or whether that computer is running.
+     *
+     * @param container the container hosting this device.
+     */
+    default void setDeviceContainer(@Nullable final DeviceContainer container) {
+    }
+
+    /**
+     * Called to serialize this device into its container's persistent storage.
+     * <p>
+     * When using this method, it may be necessary to call {@link DeviceContainer#setChanged()},
+     * similar to how it is necessary to call {@link BlockEntity#setChanged()} when the serialized
+     * representation of it changed. Unless this is called, no guarantee is made this method will
+     * be called.
+     *
+     * @return the serialized state of this device.
+     */
     @Override
     default CompoundTag serializeNBT() {
         return new CompoundTag();
     }
 
+    /**
+     * Called to deserialize this device from its container's persistent storage.
+     * <p>
+     * The passed tag will be what was last returned by {@link #serializeNBT()}.
+     *
+     * @param tag the serialized state of this device.
+     */
     @Override
     default void deserializeNBT(final CompoundTag tag) {
     }

src/main/java/li/cil/oc2/api/bus/device/DeviceContainer.java

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: MIT */
+
+package li.cil.oc2.api.bus.device;
+
+import net.minecraft.world.level.block.entity.BlockEntity;
+
+/**
+ * Back-channel for devices to send messages to their containing context, such as Bus Interfaces.
+ */
+public interface DeviceContainer {
+    /**
+     * Notifies the container managing a device it is managing has changed.
+     * <p>
+     * This should be called by devices when they need to be serialized. It is the equivalent of the
+     * {@link BlockEntity#setChanged()} method for {@link Device}s .
+     */
+    void setChanged();
+}

src/main/java/li/cil/oc2/common/bus/AbstractBlockDeviceBusElement.java

@@ -38,6 +38,17 @@ public abstract class AbstractBlockDeviceBusElement extends AbstractGroupingDevi
         super(Constants.BLOCK_FACE_COUNT);
     }
 
+    ///////////////////////////////////////////////////////////////////
+    // DeviceContainer
+
+    @Override
+    public void setChanged() {
+        final Level level = getLevel();
+        if (level != null) {
+            ChunkUtils.setLazyUnsaved(level, getPosition());
+        }
+    }
+
     ///////////////////////////////////////////////////////////////////
     // DeviceBusElement
 

src/main/java/li/cil/oc2/common/bus/AbstractGroupingDeviceBusElement.java

@@ -3,6 +3,7 @@
 package li.cil.oc2.common.bus;
 
 import li.cil.oc2.api.bus.device.Device;
+import li.cil.oc2.api.bus.device.DeviceContainer;
 import li.cil.oc2.common.util.NBTTagIds;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.nbt.ListTag;
@@ -10,7 +11,7 @@ import net.minecraft.nbt.ListTag;
 import javax.annotation.Nullable;
 import java.util.*;
 
-public abstract class AbstractGroupingDeviceBusElement<TEntry extends AbstractGroupingDeviceBusElement.Entry, TQuery> extends AbstractDeviceBusElement {
+public abstract class AbstractGroupingDeviceBusElement<TEntry extends AbstractGroupingDeviceBusElement.Entry, TQuery> extends AbstractDeviceBusElement implements DeviceContainer {
     private static final String GROUPS_TAG_NAME = "groups";
     private static final String GROUP_ID_TAG_NAME = "groupId";
     private static final String GROUP_DATA_TAG_NAME = "groupData";
@@ -170,9 +171,11 @@ public abstract class AbstractGroupingDeviceBusElement<TEntry extends AbstractGr
     }
 
     protected void onEntryAdded(final TEntry entry) {
+        entry.getDevice().setDeviceContainer(this);
     }
 
     protected void onEntryRemoved(final TEntry entry) {
+        entry.getDevice().setDeviceContainer(null);
     }
 
     protected void onEntryRemoved(final String dataKey, final CompoundTag data, @Nullable final TQuery query) {

src/main/java/li/cil/oc2/common/vm/AbstractVMItemStackHandlers.java

@@ -171,6 +171,11 @@ public abstract class AbstractVMItemStackHandlers implements VMItemStackHandlers
             super(groupCount);
         }
 
+        @Override
+        public void setChanged() {
+            onChanged();
+        }
+
         @Override
         protected ItemDeviceQuery makeQuery(final ItemStack stack) {
             return AbstractVMItemStackHandlers.this.makeQuery(stack);