Add ordered content sources and targets to the shared copy pipeline. Observe
fs.File metadata before target creation, bind fs.FS sources, and expose
fatal-stop notification while preserving native copy behavior.
Overlap source reads, hashing, ordered linear writes, and asynchronous cleanup with bounded buffers. Preserve conflicting output order, API behavior, and no-space diagnostics. Add an LTFS drive-buffer model and reproducible performance checks.