- Added comprehensive test suite for `postmortem` utility error handling, covering cleanup symbol marking, cause chain depth validation, and process exception suppression.
- Added tests for `browser-run-cancellation` ensuring proper `unhandledRejection` suppression and correct `ToolAbortError` propagation during teardown.
- Implemented `collectUnhandledRejections` helper to verify silence of process-level rejections during async race conditions in browser runs.
- Added integration-style probe tests for `postmortem` to verify that marked cleanup errors allow process survival while unmarked ones remain fatal.
