[Bug] Model resolution fails when the model ID itself contains "/" (NVIDIA NIM prefixed keys) — "Model not found" suggests the exact same ID

Description

Model references do not resolve when the model ID itself contains a slash — notably all NVIDIA NIM models, whose API-facing IDs embed the vendor prefix (e.g. the model's real ID is literally nvidia/nemotron-3-ultra-550b-a55b, so under provider nvidia the registry key is nvidia/nemotron-3-ultra-550b-a55b).

A ref written in the natural bare form nvidia/nemotron-3-ultra-550b-a55b splits at the first slash → providerID=nvidia, modelID=nemotron-3-ultra-550b-a55b (bare) → the exact-match lookup misses the prefixed key → the fuzzy suggester then offers the real key, whose rendered form is byte-identical to the requested ref, producing this error:

ProviderModelNotFoundError: Model not found: nvidia/nemotron-3-ultra-550b-a55b. Did you mean: nvidia/nemotron-3-ultra-550b-a55b?

The identical-ID suggestion is this bug's structural signature — it is generated structurally whenever this class of miss occurs, not cosmetically. It also makes the error look absurd ("did you mean the thing I just asked for?").

This cannot be worked around client-side by renaming the model key: the key IS the API-facing model id that must be sent to the NIM endpoint, so it has to keep its prefix.

Related but distinct: #39926 reports the mirror-image failure of the same first-slash split, where a URL-based provider ID breaks. This report covers model IDs containing / under a normal named provider.

OpenCode version

1.18.20

Steps to reproduce

1. Authenticate the NVIDIA provider (opencode auth login nvidia). The registry then contains slash-prefixed keys such as nvidia/nemotron-3-ultra-550b-a55b (same shape as nvidia/moonshotai/kimi-k2.6 reported in #40911).
2. Pin the model in bare form (single provider prefix) somewhere that resolves at session start — e.g. an agent file frontmatter:

   ---
   model: nvidia/nemotron-3-ultra-550b-a55b
   ---
   

3. Spawn a fresh session with that agent.
4. Observe the immediate failure below (~32 ms after session start, zero inference attempts / zero tokens).

Contrast step: reference the same model via the doubled full-key form nvidia/nvidia/nemotron-3-ultra-550b-a55b (= providerID nvidia + modelID nvidia/nemotron-3-ultra-550b-a55b). It resolves fine — which is why the same route succeeds mid-session in already-running sessions yet fails deterministically on every fresh spawn of a bare-form pin.

Observed behavior

Fresh spawn on the bare-form pin fails before any API call:

Model not found: nvidia/nemotron-3-ultra-550b-a55b. Did you mean: nvidia/nemotron-3-ultra-550b-a55b?

The suggestion is byte-identical to the requested ID. The model was simultaneously confirmed live in NVIDIA's catalog (present in /v1/models throughout the observation window), so this is a resolution defect, not catalog absence.

Same model succeeds mid-session when referenced through the already-resolved doubled form.

Expected behavior

• A bare-form ref nvidia/nemotron-3-ultra-550b-a55b should resolve to the registry key nvidia/nemotron-3-ultra-550b-a55b under provider nvidia — i.e., resolution should tolerate model IDs that themselves contain slashes.
• At minimum, the suggester should never offer a candidate whose rendered <providerID>/<modelID> is identical to the requested ref.

Suggested fix direction

1. Resolution: after splitting <provider>/<rest> and missing on exact match, attempt to interpret <rest> as the full model ID (exact/suffix match against that provider's keys) before falling back to fuzzy suggestions — this makes the bare form resolve the prefixed key.
2. Suggester hygiene: filter out suggestions equal to the requested ref. "Did you mean X?" where X === requested is misleading and masks the actual failure mode.
3. Diagnostics (optional): when the would-be suggestion equals the request, emit a distinct message (e.g. "model ID may itself contain '/'; try doubling the provider segment") so scripts can recover.

Impact

Any agent/config pin or script that names a NIM model in the natural bare form fails deterministically at fresh-session spawn while the same model keeps working in sessions that were started interactively — intermittent-looking in aggregate, deterministic-by-form in reality. Easy to misdiagnose as provider outage/rate limiting.

Environment: opencode 1.18.20 standalone binary, macOS (darwin arm64), NVIDIA NIM endpoint https://integrate.api.nvidia.com/v1.