Add rate limiting for import

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

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

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

No files, entry points, or tests are named. Start by locating the import handlers and existing error-handling paths, then determine the intended rate-limit behavior and required error details. Done means the import path enforces the agreed limit and reports sufficiently descriptive errors, with relevant tests updated or added.

Written by the indexing model from the issue text.