Readiness covered only the auth store, so a gateway whose worker exe was
missing or of the wrong architecture reported ready while every OpenSession
failed. The new ready-tier check worker-executable applies the launcher's own
rule (path resolution, .exe, presence, PE architecture), now shared as
WorkerExecutableValidator.ResolveAndValidate, and reports only the launch
error code (the endpoint is anonymous). The session check stays on the
active tier, so zero sessions keeps readiness green.
The bounded Galaxy SQL check is not in this change: its tier, failure status
and probe cadence need a decision (see the issue).
Tests: WorkerExecutableHealthCheckTests (healthy, missing, wrong architecture,
and the ready-tier registration, which fails without the wiring).
Joseph Doherty