fix(cli): retry transient sandbox sync disconnects

[elezar]

Summary

Retry sandbox upload and download operations when a gateway handoff interrupts the underlying transport. Retries rebuild the SSH session for each attempt and remain limited to typed transient failures; validation, local permission, remote command, and other permanent failures still return immediately.

Related Issue

Extracted from #1868 so the generally applicable CLI behavior can be reviewed independently.

Changes

• Retry complete upload and download attempts up to four times after transient disconnects.
• Preserve typed gRPC connection/status, SSH exit, and tar-stream I/O errors for classification.
• Retry only gRPC Unavailable, connection transport errors, BrokenPipe, ConnectionReset, UnexpectedEof, and SSH exit 255.
• Add deterministic async coverage for retry-then-success, retry exhaustion, and immediate permanent failure.

Testing

• mise run pre-commit passes
  • Attempted, but the local task failed during environment setup: grpc_tools was unavailable while the new venv was still being populated, and workspace Clippy could not find z3.h outside the Nix environment. Format, license, Helm, and Markdown checks passed.
• nix develop -c cargo test -p openshell-cli --lib (195 tests)
• nix develop -c cargo clippy -p openshell-cli --all-targets -- -D warnings
• E2E tests added/updated (not applicable; deterministic unit coverage exercises the retry policy)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.