⚠️ refactor: Use Error Content Part Instead Of Throwing Error for Agents

[danny-avila]

Summary

I refactored the agent error handling workflow to push an error content part instead of throwing errors during execution. This change guarantees that error messages are encapsulated within a structured content part and excluded from subsequent message payloads for smoother processing and display.

• Updated the agent client in api/server/controllers/agents/client.js to append an error content part with a formatted message instead of throwing an error.
• Modified the message formatting in api/app/clients/prompts/formatMessages.js to skip any parts marked as ERROR.
• Added a comprehensive test in api/app/clients/prompts/formatAgentMessages.spec.js to verify that error parts are excluded from the final AIMessage content.
• Adjusted the error rendering in client/src/components/Chat/Messages/Content/Part.tsx to display the error message from the ERROR property when available.

Testing:

• Ran the updated unit tests to confirm that error messages are handled as content parts and are omitted from formatted outputs.
• Simulated agent error scenarios to ensure the correct error message is pushed and rendered without causing unintended interruptions.

Checklist:

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented complex areas of my code as needed
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective
• Local unit tests pass with my changes
• Any dependent changes have been merged and published in downstream modules