Safe mode breaks Tinker training, loopback-only hosts crash at deploy, checkpoints unusable from stock Tinker SDK #298

• I have searched existing issues, and this is a new bug report.

Bug Description

Three problems when running Twinkle 0.5.1 in an isolated container and using it from the stock Tinker SDK (source links at v0.5.1):

1. Safe mode breaks Tinker training.
   • With TWINKLE_TRUST_REMOTE_CODE=0, every forward_backward fails with Twinkle does not support Callable or Type inputs in safe mode. The check is check_unsafe on the remote-call path (infra/init.py#L573).
   • So operators can't turn remote-code trust off, and it defaults to on.
2. Loopback-only hosts crash at deploy.
   • Under e.g. docker run --network none, find_node_ip() skips every 127.* address and returns None (utils/network.py#L15-L28).
   • That None becomes MASTER_ADDR (ray_helper.py#L336), and the deployment fails with TypeError: runtime_env['env_vars'] must be of type Dict[str, str].
   • Also, .locks is created in the CWD (utils/parallel.py#L9), which fails when the CWD is read-only.
3. Checkpoints can't be used from the stock Tinker SDK.
   • save_weights_for_sampler() returns twinkle://... paths, which the unpatched SDK rejects (ValueError: Invalid tinker path). There's also no archive/download endpoint.
   • name is ignored, and each save deletes the previous sampler weights (checkpoint_manager.py#L241-L285), so earlier returned paths go stale.

How to Reproduce

1. Set TWINKLE_TRUST_REMOTE_CODE: "0" in the model deployment's env_vars, then call forward_backward(data, "cross_entropy").
2. Start ray start --head --node-ip-address=127.0.0.1 and twinkle-server launch inside a --network none container.
3. With tinker==0.16.1, call get_checkpoint_archive_url_from_tinker_path(tc.save_weights_for_sampler(name="x").result().path).

Additional Information

Suggested fixes:

1. Exempt Twinkle's built-in loss and template classes from check_unsafe.
2. In find_node_ip(), fall back to 127.0.0.1 (or the Ray node IP), and put .locks under TWINKLE_HOME or the temp dir.
3. Return tinker://-compatible paths, add the Tinker archive endpoint, and honour name. That would let separate evaluators load trained adapters without patching the SDK.

Environment: twinkle-kit 0.5.1, ray 2.58.0, Ubuntu 24.04 container, tinker 0.16.1.