Examples and Practice: Agent State and Messages

Worked Practice

1. Write one paragraph explaining Agent State and Messages to a beginner.
2. Draw the smallest diagram that shows input, transformation, output, and failure mode.
3. Build or outline a tiny artifact connected to: Build a manual ReAct-style agent.
4. Measure it with: Track steps, success, invalid actions, and stop reasons.
5. Add one failure case to your learning log.

Mini Project Drill

Create a file named notes/agent-state-and-messages.md in your project workspace. Include:

• the problem Agent State and Messages solves
• the simplest implementation or design
• the measurement you used
• one example input
• one expected output
• one failure case
• one decision you would make from the result

Check Your Understanding

Question	What a strong answer includes
Why does Agent State and Messages matter?	It connects to a tool-using agent with typed tools, memory, traces, task evals, prompt-injection tests, and an architecture readme. and names a practical risk.
How would you test it?	It uses a small repeatable case and a measurable expected result.
What breaks first?	It names a specific failure mode, not only "the model is bad".
When should you move on?	When the artifact works on a realistic case and one edge case.

Stretch Exercise

Revisit the same drill after finishing the next part. Update the note with what changed. This is how isolated concepts become connected system judgment.

Return to 6.1.1 Agent State and Messages.