Recover attribution from sandboxed checkpoints

[svarlamov]

Summary

• Treat imported sandboxed Bash and post-file-edit checkpoint metrics as candidates in the existing repo-and-mtime attribution recovery flow.
• Preserve the shared candidate ranking and session attribution logic while keeping commit-metadata recovery restricted to session events.
• Add TestRepo E2Es proving both sandboxed file edits and Bash edits are marked as likely AI code after commit.

Testing

• task build
• task fmt
• task lint
• task test

---

[svarlamov]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Recover attribution from sandboxed checkpoints #1914 👈 (View in Graphite)
• Spool sandboxed checkpoints for daemon import #1913
• Refuse daemon startup in agent sandboxes #1912
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.