fix(cli): preserve state after interrupted runs

[c8dhjp4tyv-bit]

Summary

• checkpoint the latest run state into the in-memory continuation ref on abort
• retain the latest snapshot after non-abort run errors so the next prompt continues history
• guard late snapshots and results from superseded runs with a generation token
• add abort checkpoint callback regression coverage

Fixes #1054

Validation

• targeted CLI tests: 106 passed
• CLI typecheck: existing missing tar and react-dom/server declarations; no changed-file errors
• Prettier check passed
• git diff --check passed