Bounded, no-follow read of an already-delivered artifact under the workspace
uploads/ directory, for the ACP consumer that embeds the blob. The artifact
is opened once beneath its parent directory handle (cap-std, no-follow), its
size is taken from that handle, and at most MAX_DELIVER_FILE_BYTES + 1 bytes
are read from the same handle. A workspace writer that grows or replaces the
content-addressed file between the tool’s write and this read therefore cannot
cause an unbounded read, and a replacement symlink is refused, not followed.