Constant WORKER_STDERR_PREFIX 

pub const WORKER_STDERR_PREFIX: &str = "jemalloc-alloc-worker:";

Stderr line prefix the ktstr-jemalloc-alloc-worker binary prepends to every fail-fast diagnostic it emits (missing argv, bytes=0, thread self-check, procfs unreadable, ready-marker write fail). Exported as a pub const so host-side integration tests can assert against the binary’s emitted literal without duplicating it — a rename or a typo on either side shows up here in one place instead of silently desynchronizing.

The trailing space that separates the prefix from the message body is NOT part of this constant: call sites write {WORKER_STDERR_PREFIX} … so the space remains a formatting concern, and test-side substring checks can match on the prefix alone regardless of the specific separator the worker chooses.