Each coverage shard now merges its own raw profiles into one sparse
.profdata with the archive toolchain's llvm-profdata and uploads only
that. The scan job merges the shard profiles instead of downloading
every raw profile beside the test archive, which on 11 Nov 2026 filled
the runner for vectorcraft (four ~7 GB zipped profraw artifacts).
A raw profile llvm-profdata cannot read, such as one cut short by a
test process that crashed while writing it (lightcraft, 11 Nov 2026),
now fails its shard with an error naming the file, instead of being
uploaded and failing the scan's merge.
Single-shard callers keep the cargo llvm-cov path unchanged.
FredApps