[aw] Copilot PAT auth failure

### Workflow Failure

**Workflow:** [Runtime Failure Observer (xharness)](https://github.com/dotnet/xharness/blob/main/.github/workflows/runtime-failure-observer.agent.md)
**Branch:** main
**Run:** https://github.com/dotnet/xharness/actions/runs/30747996085

> [!WARNING]
> **Engine Failure**: The `copilot` engine terminated unexpectedly.

**Last agent output:**
```
Changes +0 -0
Duration 3s
Resume copilot --resume=feee3906-392b-48aa-b74c-f1ace225cfce
● Request failed (transient_auth_error). Retrying...
● Request failed (transient_auth_error). Retrying...
Authentication failed with provider at http://172.30.0.30:10002 (HTTP 401).
Check your COPILOT_PROVIDER_API_KEY or COPILOT_PROVIDER_BEARER_TOKEN.
Changes +0 -0
Duration 3s
Resume copilot --resume=227870f6-2d04-41fb-aa37-c2615970baea
```

### Action Required

**Assign this issue to an agent** to debug and fix the issue.

Debug with any coding agent

Use this prompt with any coding agent (GitHub Copilot, Claude, Gemini, etc.):

````
Debug the agentic workflow failure using https://raw.githubusercontent.com/github/gh-aw/main/debug.md

The failed workflow run is at https://github.com/dotnet/xharness/actions/runs/30747996085
````

Manually invoke the agent

Debug this workflow failure using your favorite Agent CLI and the `agentic-workflows` prompt.

- Start your agent
- Load the `agentic-workflows` skill from `.github/skills/agentic-workflows/SKILL.md` or
- Type `debug the agentic workflow runtime-failure-observer.agent failure in https://github.com/dotnet/xharness/actions/runs/30747996085`

> [!TIP]
>
> Stop reporting this workflow as a failure
>
> To stop a workflow from creating failure issues, set `report-failure-as-issue: false` in its frontmatter:
> ```yaml
> safe-outputs:
> report-failure-as-issue: false
> ```
>
>

> Generated from [Runtime Failure Observer (xharness)](https://github.com/dotnet/xharness/actions/runs/30747996085) · [◷](https://github.com/search?q=repo%3Adotnet%2Fxharness+is%3Aissue+%22gh-aw-workflow-id%3A+runtime-failure-observer.agent%22&type=issues)
> - [x] expires on Aug 9, 2026, 12:36 PM UTC

Start with .github/workflows/runtime-failure-observer.agent.md and the linked workflow run. Read the agentic-workflows skill at .github/skills/agentic-workflows/SKILL.md, then trace the Copilot provider authentication configuration and the reported HTTP 401. Done means the workflow can authenticate successfully and no longer terminates with transient_auth_error.

Written by the indexing model from the issue text.