The trust tier was read off the caller-supplied worker_id, so a JWT user who
knew any trusted worker's id could claim as it — draining and poisoning the
trusted queue and bypassing the untrusted-worker quarantine entirely.
Claim now requires a JWT caller to own the worker it acts as; a shared-token
caller (lab operator) may still act as any worker. Claim is the sole grantor of
a lease, so this also protects the downstream heartbeat/result/failure paths.
Tests: reject claim as another user's worker; allow claim as own worker.
Efremenko Arhip
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