Every SDK module imports its exceptions from one file, _errors.py

The exception hierarchy in _errors.py (ClaudeSDKError, CLIConnectionError, CLINotFoundError, ProcessError, ResultError, CLIJSONDecodeError, MessageParseError) is imported directly by the CLI transport, ClaudeSDKClient, the control protocol query, the message parser and the package entry point. None has a fallback. A breaking change to this file reaches all five, and through the transport it reaches the internal client that drives one-shot queries.

Impact: Renaming or reshaping an exception breaks the public exports and every place that catches or raises it, so callers lose their error handling at once.

Recommendation (small effort): Treat _errors.py as a frozen public contract: add new exception classes as subclasses and keep existing names and constructor arguments stable. Cover the hierarchy with a test that imports every name the package entry point re-exports.