WRITE_CHECKPOINT reply header: data.files is the list of file paths
actually written by rank 0 (protocol.md §WRITE_CHECKPOINT). v1 always
writes a single file; files is kept as a JSON array for forward
compatibility with a future multi-file checkpoint format.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| character(len=*), | intent(in) | :: | req_id | |||
| character(len=*), | intent(in) | :: | files(:) | |||
| integer(kind=int8), | intent(out), | allocatable | :: | header_bytes(:) |