BYOK with external Azure AI Foundry deployment — model not found in proxy catalog (HTTP 404)

[arthurfvives]

When configuring BYOK mode with engine: copilot to route inference to a custom model deployment on Azure AI Foundry,
the agent step fails immediately with:

Model '<model-name>' not found on provider at http://172.30.0.30:10002 (HTTP 404)

This happens regardless of whether COPILOT_MODEL is set to the generic model family name or the deployment name.

From the logs, the harness fetches a fixed list of ~25 models from the proxy (api-proxy:10002/models). These appear
to be the standard GitHub Copilot models. The external BYOK provider's deployment never appears to be registered or
discoverable in that list.

Expected behaviour: In BYOK mode, inference requests for a model that exists on the external provider should be
routed there — either by merging the external provider's model list into the proxy catalog, or by accepting any
COPILOT_MODEL value when COPILOT_PROVIDER_BASE_URL is set.

Config used:

 engine:
   id: copilot
   env:
     COPILOT_PROVIDER_BASE_URL: ${{ secrets.COPILOT_PROVIDER_BASE_URL }}
     COPILOT_MODEL: gpt-5-mini-mycustom (also tried gpt-5-mini, same result)
     COPILOT_PROVIDER_API_KEY: ${{ secrets.COPILOT_PROVIDER_API_KEY }}
     COPILOT_PROVIDER_TYPE: azure
     COPILOT_PROVIDER_WIRE_API: responses
     COPILOT_PROVIDER_MODEL_ID: gpt-5-mini-mycustom

I followed the BYOK documentation as closely as I could, so it's entirely possible I'm misconfiguring something (first time working with Foundry too)
Thanks in advance

[arthurfvives]

Update: Changing COPILOT_PROVIDER_TYPE from azure to openai made the run complete without errors. However, I'm not confident BYOK actually activated.

The activation summary shows:

engine id: copilot
engine name: GitHub Copilot CLI
model: claude-sonnet-4.6

But the agent itself reports it's running on my custom deployment (gpt-5-mini-mycustom). After digging into the agent artifact, I found:

• sandbox/firewall/logs/access.log — the only outbound HTTPS connection was to api.githubcopilot.com:443. No traffic to my Azure AI Foundry endpoint.
• sandbox/firewall/logs/api-proxy-logs/models.json — "openai": { "configured": false }, "copilot": { "target": "api.githubcopilot.com" }
• agent-stdio.log — health check says ✓ Copilot CLI offline+BYOK mode configured, but the proxy appears to have fallen back to GitHub Copilot anyway

The agent's self-report seems to be based on reading its own COPILOT_MODEL/COPILOT_PROVIDER_MODEL_ID env vars rather than reflecting its actual backend.

My question: Should the activation summary model field reflect the BYOK model when BYOK is active? If so, claude-sonnet-4.6 being shown there suggests BYOK never routed to my provider — and I still don't know why the proxy ignores the secret.