How does Comfy API v2 let one client talk to Comfy Cloud, a dedicated deployment and a self-hosted ComfyUI, and what are its poll-first and output-URL rules?

Problem. Orchestrating ComfyUI jobs from an application with durable job ids. Conditions. Comfy API v2 as documented 2026-10-23 (changes within v2 additive; breaking changes ship as v3). Method. One contract is served by three surfaces: Comfy Cloud (cloud.comfy.org), per-deployment endpoints (https://{deployment}.run.comfy.app, pinned environment) and open-source ComfyUI through comfy-api-proxy (pip install comfy-api-proxy; proxies 127.0.0.1:8188 and serves v2 on 127.0.0.1:8189; --comfyui and --port change either; --comfyui-base-dir enables uploading model files). Design rules: poll first (GET /api/v2/jobs/{id} is authoritative, SSE is only an enhancement), everything resumable until expires_at, assets content-addressed with a server-computed blake3 hash, follow returned links instead of building URLs. Output.url on a job output is an authenticated content route (401 for a third party); a signed storage URL is the shareable one but short-lived (the docs give about 6 hours on Comfy Cloud, today). The proxy binds loopback only and has no authentication unless a static bearer token is configured; the docs warn to add a token or an authenticating reverse proxy before exposing it. The older v1 Cloud API is marked deprecated but still holds queue, interrupt and object_info. Pricing is intentionally not covered. Failure modes. Embedding Output.url in public pages (401 for viewers); relying on SSE alone; exposing the proxy beyond loopback unauthenticated. Limitations. Vendor-documented; no calls made. Version and date. Docs undated, fetched 2026-10-23. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Hosted behaviour untested. URL lifetime is a stated snapshot ('today'). Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://docs.comfy.org/api-reference/v2/overview.md",
      "note": "Design Principles; Authentication warning; Output URLs"
    },
    {
      "url": "https://docs.comfy.org/development/comfyui-server/api-proxy.md",
      "note": "Design Principles; Authentication warning; Output URLs"
    }
  ]
}