Updates the agent tutorial to explain the JSON schema grammar for the
EXTRACT command, including selectors, attributes, and nested fields.
Adds examples for multi-line input and clarifies recording behavior.
Moves script logic to `browser/script/` for shared use. Implements
message rollback on API failure, caches environment variables, and
fixes a potential panic in the spinner.
- Relocate Command, Recorder, and Verifier to `src/browser/script/`
- Implement message rollback on API and synthesis failures in Agent
- Cache `LP_*` environment variables process-wide with mutex protection
- Fix potential panic in Spinner during backward clock jumps
- Improve Recorder to handle write failures and multi-line comments
- Update documentation regarding attachments and path safety
