The second live test showed nvidia and radeon each renting their OWN pod
for 'capability:embeddings' — two GPUs, two bills, while max_pods said 1.
Same root cause as the reaper bug: one engine per GPU, each with its own
pools, none able to see the others.

Before renting, a pool now looks in the shared registry for a healthy pod
another process already has for the SAME pool key, and borrows it. The
registry entry carries the URL, recorded once the pod is serving.

A borrowed pod is released, never terminated: its owner holds the
lifecycle and the bill, and killing it would take it away from the engine
still using it. It is also billed at 0 here, so the cost is not
double-counted against the caps.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY