Composite model catalogs expose exact account model_mapping aliases, but request routing only considered explicit routes or model-name detection. Unprefixed aliases were selectable but unroutable.
Resolve unique exact account ownership before the detector, keep explicit routes authoritative, and fail closed when an alias is claimed across platforms.
Composite model routes support a match_type: prefix mode with an optional
upstream_model. Leaving upstream_model empty is meant to pass the concrete
requested model through to the upstream, but every request matching the prefix
collapsed to the route's public_model instead. A route with
public_model=deepseek-v4, match_type=prefix and an empty upstream_model
forwarded both deepseek-v4-flash and deepseek-v4-pro upstream as deepseek-v4.
Root cause: normalizeCompositeRouteInput backfilled an empty upstream_model with
public_model at save time, so CompositeRouteResolver.Resolve never reached its
"upstreamModel == '' -> concrete requested model" fallback.
- Skip the backfill for prefix routes only; an empty upstream_model stays empty
and Resolve passes the concrete requested model through.
- exact routes keep the backfill (model == public_model, so persisted/display
contract is unchanged).
- Explicit upstream_model still forwards that fixed model in every mode.
- Frontend: add an upstream_model hint (zh/en) documenting empty = passthrough.
Long Li