7 tests pin the Execute early-return surface that runs without a
filer or S3 dial: nil request / nil Job / nil sender all error;
foreign JobType errors with the offending name in the message; no
S3 endpoints in cluster context errors (Execute is stricter than
Detect — the admin shouldn't have routed the job there); missing
filer_grpc_address parameter errors (proposal must have been tampered
with or dropped); empty JobType is accepted as broadcast routing and
flows through to the next validation step. The dial path itself is
intentionally not covered here — those tests would need an in-process
gRPC server and belong with the integration suite.