[Bug]: provider vanishes when /v1/models discovery returns 401; Agent Plan needs manual model specification #329

Summary

With adapter: anthropic (and similarly other adapters that rely on OpenAI-style model discovery), OpenCodex runs model discovery via:

GET <baseUrl>/v1/models?limit=1000

Some upstreams authorize the API key for inference, but not for the models list endpoint. A concrete case is Volcengine Ark Agent Plan / Coding Plan:

• inference endpoints such as /v1/messages work
• GET /v1/models returns 401 AuthenticationError

When discovery fails and no customModels entry exists, the entire provider silently disappears from the Models tab / Claude model discovery. There is no UI path to manually specify a model id, even though the provider is usable after a manual custom-model registration.

Environment

• opencodex: 2.7.33
• macOS, Apple Silicon
• Upstream: Volcengine Ark Agent Plan / Coding Plan
• Example model: glm-5-2 / glm-5-2-260617
• Example base URLs:
  • Agent Plan Anthropic path: https://ark.cn-beijing.volces.com/api/plan
  • Coding Plan Anthropic path: https://ark.cn-beijing.volces.com/api/coding
• Provider config shape: adapter: anthropic, key auth

Current behaviour

1. Provider key is valid for inference:
   • POST <baseUrl>/v1/messages → 200, model responds correctly
2. Same key fails model discovery:
   • GET <baseUrl>/v1/models?limit=1000 → 401 AuthenticationError
3. service.log shows something like:
   • Provider model discovery for "<name>" failed with HTTP 401 [urlClass=provider-models, fallback=configured].
4. If no custom model has been registered yet, the provider vanishes from:
   • OpenCodex Models tab
   • Claude model discovery
5. There is no dashboard / model-list UI affordance to manually enter a known model id as a fallback when discovery fails.

Expected behaviour

When model discovery fails (especially with 401 / permission-limited plan keys), OpenCodex should not hide a still-usable provider.

Specifically:

1. Keep the provider visible even if /v1/models fails.
2. Support manual model specification at the model-interface / provider layer (config and preferably dashboard UI), e.g.:
   • default model
   • custom model ids / catalog entries
   • configured fallback models used when discovery fails
3. Surface discovery failure clearly (401, discovery failed badge / log-backed reason), instead of silent disappearance.
4. Once a model is manually specified, expose it to Codex / Claude as a normal selectable model.

Workaround found

Manually register the known model via:

POST /api/custom-models

After that, the provider reappears and inference works immediately.

This proves:

• discovery failure ≠ inference failure
• Agent Plan can be used successfully once the model id is specified manually
• the missing piece is a first-class manual model entry path when discovery is unavailable

Minimal redacted reproduction

# 1) Inference works
curl -sS -X POST 'https://ark.cn-beijing.volces.com/api/plan/v1/messages' \
  -H 'x-api-key: <REDACTED>' \
  -H 'anthropic-version: 2023-06-01' \
  -H 'content-type: application/json' \
  -d '{
    "model": "glm-5-2",
    "max_tokens": 32,
    "messages": [{"role":"user","content":"Reply exactly: OK"}]
  }'
# → HTTP 200

# 2) Model list fails with the same key
curl -sS 'https://ark.cn-beijing.volces.com/api/plan/v1/models?limit=1000' \
  -H 'x-api-key: <REDACTED>'
# → HTTP 401 AuthenticationError

# 3) OpenCodex result without customModels:
# provider disappears from Models tab / discovery UI

# 4) After manual custom model registration:
# provider reappears and inference through OpenCodex works

Why this matters for Agent Plan

Volcengine Agent Plan is a practical multi-model coding/plan product. In practice:

• plan keys may be allowed to call chat/messages endpoints
• plan keys may not be allowed to list models
• the usable model ids are still known to the user (e.g. glm-5-2)

So OpenCodex currently creates a false “provider broken” state for a working Agent Plan route. Manual model specification should be a supported primary path, not only a hidden recovery API.

Suggested implementation notes

Possible backward-compatible approaches:

1. Treat configured defaultModel / customModels as durable catalog entries independent of discovery success.
2. Add an explicit provider/model field such as manualModels or strengthen existing custom-model support so discovery failure never removes configured models.
3. In dashboard / model interface:
   • show provider even when discovery fails
   • allow adding model ids manually
   • badge the provider with discovery failed (401) or similar
4. Keep discovery as best-effort enrichment, not a hard gate for provider visibility.

Additional context

• Related prior report on Responses path construction for Agent Plan: [Bug]: Volcengine Ark Agent Plan Responses URL incorrectly appends /v1 #289
• Related anthropic streaming issue already fixed on dev: [Bug]: anthropic adapter returns empty content (adapter_eof / 0 tokens) for streaming requests against upstreams that emit reasoning blocks (Kimi k3) #312
• This report is specifically about model discovery + manual model specification, not inference correctness after a model is registered.
• No API keys or credentials are included.

Checks

• I searched existing provider and compatibility issues.
• The request and response details were redacted.
• The expected behaviour is based on concrete reproduction: Agent Plan inference works, /v1/models returns 401, and manually specifying the model restores usability.