A blob hash read back from the downloaded snapshot database or the store
listing was trusted unchecked. A hostile remote could set a hash such as
"aa/../../etc" and have a decrypted blob written outside the cache
directory, or feed a short or negative value that panicked a command.
blobDiskCache.path now refuses any key with a path separator, and ReadAt
rejects a negative offset or length, bounding with length > size-offset so
a sum cannot overflow past the check. A new isBlobHash helper (a plain
function, since the packer stores temp-placeholder-{uuid} as a hash) gates
FetchBlob, shallow and deep verify, and restore: buildBlobIndexes rejects
every hash from the snapshot database before any fetch. The blobs/ and
metadata/ listings skip a non-conforming name, and short-hash prefixes in
log and error text go through a shortHash helper that cannot panic.
verify's chunk reader rejects a negative length and streams the chunk.
Model: opus-4-8
sneak