feat(agent-interface): introduce AgentBase abstract class as the interface for agent classes to implement

[awsarron]

Description

feat(agent-interface): introduce AgentBase abstract class as the interface for agent classes to implement

Related Issues

#573

Documentation PR

TODO

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• [N/A] I have added any necessary tests that prove my fix is effective or my feature works
• [TODO] I have updated the documentation accordingly
• [TODO] I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

❌ Patch coverage is 89.09091% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/strands/agent/base.py	78.57%	6 Missing ⚠️

📢 Thoughts on this report? Let us know!

[dbschmigelski]

🥳

Just calling out here if anyone looks back

• structured_output() is deprecated so it wasn't added
• Direct tool calling also was not added

[mkmeral]

should we use Protocol instead?

[zastrowm]

@pgrayy has also called out that Protocols should be preferred in general over base-classes; it would also enable us to specify the properties as normal fields instead of getters

[mkmeral]

nit: How would this relate to MultiAgentBase? I personally want to get rid of it, but given that AgentBase is more extensive than MultiAgentBase, it might not be possible, right?

[zastrowm]

@pgrayy has also called out that Protocols should be preferred in general over base-classes; it would also enable us to specify the properties as normal fields instead of getters

[zastrowm]

Can you update the PR description indicating the purpose of the base class - e.g. is it just for agents or is it meant to represent things in-place of an agent (like humans) as the tracking issue #573 calls out.

Specifically, if we were starting fresh, what would implement this? MultiAgent primitives? A2AAgent, etc?

[zastrowm]

For the use-cases that we're targeting, will invocation_state and structured_output_model be supported? For instance, for multi-agent, I think structured_output is not supported but invocation_state is?