Replace string-based session comparison with array-based approach:
- Store before_sessions in an array instead of pipe-delimited string
- This is more robust against word-splitting issues in bash
- Skip base_session_id and pm_agent_session_id explicitly
- Compare each after-session against the before array
This approach is more reliable when multiple agents fork concurrently
because it properly compares each session ID individually rather than
relying on regex matching in a string.
Fixes#81
3df99d571f