Each `ensure_service()` already returns a base URL, so a worker can be
pointed at a service running elsewhere — another host, a container, a
rented RunPod pod — without anything downstream noticing. Only the TTS
backends had that escape hatch (parler/melo, checked at the caller);
now the check lives in the workers themselves, per-model via
`service_url` in the config plus a CODERAI_*_SERVICE_URL env var:

  vllm, ds4, kt, h3, pyannote, melotts, canary, crisperwhisper, parler

Each verifies the remote's health check before returning it, so a stale
or wrong URL fails loudly instead of surfacing as a confusing timeout
later. vLLM additionally checks that the remote actually serves the
requested model — the OCR path asks for surya-2 by name, and a generic
remote vLLM would otherwise be proxied silently.

colibri/k3 are left out: they speak a stdin/stdout mux protocol, not
HTTP, so there is no URL to redirect.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY