Builds backend-specific fallback fetch URLs from the policy's ordered
default_blob_endpoints and the attachment's ciphertextSha256
(features/encrypted-media.md — Locator Kinds). Endpoint order is the
fallback priority and is preserved.
Only blossom-v1 endpoints produce a URL (Blossom GET /<sha256>); other
kinds need backend-specific rules and are skipped. Whether to actually fetch
a loopback-http endpoint is a separate local dev/test decision.
Builds backend-specific fallback fetch URLs from the policy's ordered
default_blob_endpointsand the attachment'sciphertextSha256(features/encrypted-media.md— Locator Kinds). Endpoint order is the fallback priority and is preserved.Only
blossom-v1endpoints produce a URL (BlossomGET /<sha256>); other kinds need backend-specific rules and are skipped. Whether to actually fetch a loopback-httpendpoint is a separate local dev/test decision.