Side Effects and Isolation

A function has a "side effect" if it interacts with the outside world (Database, API, File System).

Idempotency

Ideally, tools should be idempotent.

• read_file() is safe to run 10 times.
• append_to_file() is NOT. If the graph retries, you duplicate the content.

Isolation Layers

Wrap side-effect tools in an "Execution Layer" node. When testing, you can swap this node for a "Mock Node" that just logs "I would have sent an email" without actually sending it. This allows you to test the logic of the graph without spamming users.