- Add pytest-xdist to the CI Dockerfile (image -> v10).
- Worker-isolate TEST_DATA_DIR (PYTEST_XDIST_WORKER) so concurrent xdist
workers never collide on shared-filesystem fixtures.
- Register a 'ci' marker and tag a fast representative subset of integration
tests (basic TCP, incremental, compression, delete, basis, append).
- ci.yaml: lint + build + unit + the marked subset (-n4) on every PR; the
full integration suite plus sanitizer/fuzz/coverage/valgrind run only on
push to dev/main.
- Integration step runtime drops from ~860s (serial) to ~230s (-n4); the PR
gate lands well under ~3 minutes.
- CLI: --append/--append-verify acceptance (parse + imply --incremental,
validate) and incompatibility rejection with -s and --whole-file; both
removed from the unimplemented reject list.
- Config: on-the-wire append/append_verify round-trip.
- Unit: append_resume_eligible / append_tail_length pure resume math.
- Integration (test_append.py): matching-prefix resume is byte-identical and
tail-only (wire bytes << source size); --append with a wrong prefix keeps
prefix+tail (rsync parity) while --append-verify detects the mismatch and
falls back to a byte-exact full transfer; --append with --inplace and -m.