Add rate limiting for serialization

**Problem**
When working with core, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue names no files, tests, or entry points, so first locate the serialization and error-handling code in the core of the terminal agent. Clarify whether the goal is rate limiting, more descriptive errors, or both; done should include the agreed behavior and coverage for the relevant failure cases.

Written by the indexing model from the issue text.