When multiple custom providers expose the same model ID (e.g. baidu,
huoshan, and liantong all offering glm-5.1), only the first provider's
entry was shown in the model dropdown.
Root cause (backend): used the bare model ID as the
dedup key, so the second and subsequent providers with the same model
were silently skipped.
Root cause (frontend): stripped the @provider: prefix before
comparing, so @custom:baidu:glm-5.1 and @custom:huoshan:glm-5.1 were
treated as duplicates.
Fix:
- Backend: change _seen_custom_ids key to '{slug}:{model_id}' so each
provider's models are tracked independently.
- Frontend: add _providerOf() helper and deduplicate on the composite
(normId, provider) key instead of normId alone. Bare model IDs
(without @provider: prefix) still deduplicate on normId for backward
compatibility.
a6599cd68e