Update data documentation

**Problem**
When working with types, 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 type-handling and error-reporting paths in the terminal agent. Compare current failures with the requested behavior and define which type errors need more detail; done means the messages are consistently descriptive and the relevant error-handling checks pass.

Written by the indexing model from the issue text.