transformers

b36d9cf0 - Fix CKPT visibility: write to /tmp file, controller drains+emits; 1s interval

Fix CKPT visibility: write to /tmp file, controller drains+emits; 1s interval Worker CKPT lines written to /tmp/ckpt_{gw}.log (not stderr, which is buffered during test execution). Controller reads new lines from each worker file every poll cycle and writes them directly to stderr, so all CKPT checkpoints (load_dataset, map, backward, etc.) appear in CI. Also change controller poll interval 2s → 1s (O(1) _children() makes this cheap). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>