#2912 - Initial layout of extensible_actions documentation page

docs/source/how_to_guides/extensible_actions.rst

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     © Crown-owned copyright 2025, Defence Science and Technology Laboratory UK
+
+
+Extensible Actions
+******************
+
+
+Changes to Actions class Structure.
+===================================
+
+Actions within PrimAITE have been updated to inherit from a base class, AbstractAction, standardising their format and allowing for easier creation of custom actions. Actions now use a ``ConfigSchema`` to define the possible configuration variables, and use pydantic to enforce correct parameters are passed through.
+
+
+Developing Custom Actions.
+==========================
+
+Custom actions within PrimAITE must be a sub-class of `AbstractAction`, and contain 3 key items:
+
+#. ConfigSchema class
+
+#. Unique Identifier
+
+#. `from_request` method.
+
+
+ConfigSchema
+############
+
+The ConfigSchema sub-class of the action must contain all `configurable` variables within the action, that would be specified within the environments configuration YAML file.
+
+
+Unique Identifier
+#################
+
+When declaring a custom class, it must have a unique identifier string, that allows PrimAITE to generate the correct action when needed.
+
+.. code:: Python
+
+    class CreateDirectoryAction(AbstractAction, identifier="node_folder_create")
+
+        config: CreateDirectoryAction.ConfigSchema
+
+        class ConfigSchema(AbstractAction.ConfigSchema):
+
+            verb: ClassVar[str] = "create"
+            node_name: str
+            directory_name: str
+
+        def form_request(cls, config: ConfigSchema) -> RequestFormat:
+            return ["network",
+                    "node",
+                    config.node_name,
+                    "file_system",
+                    config.verb,
+                    "folder",
+                    config.directory_name,
+                ]
+
+The above action would fail pydantic validation as the identifier "node_folder_create" is already used by the `NodeFolderCreateAction`, and would create a duplicate listing within `AbstractAction._registry`.
+
+
+from_request method
+###################
+
+PrimAITE actions need to be have a `from_request` method, which can be passed to the `RequestManager` for processing. This allows the custom action to be actioned within the simulation environment.