[ci-scan] Build break: PALTests Send to Helix fails with SYSTEM_ACCESSTOKEN variable not found on runtime-coreclr outerloop

## Build Information
Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1560135
Build error leg or test failing: linux-arm64 / linux-x64 / osx-arm64 / osx-x64 / linux_musl-* Debug PALTests - Send job to Helix (Unix) (paltests.proj)

KBE authoring guidance (ci-failure-scan)

- `Error Details` is for readers. Paste the full exception, stack trace, or build error excerpt so the failure is understandable without opening the raw log.
- Build Analysis parses only the single JSON block under `Error Message`.
- `ErrorMessage` is a case-sensitive ordinal `String.Contains` substring copied verbatim from the failing log.
- Set `BuildRetry` to `true` only for a clear infrastructure retry case. `ExcludeConsoleLog` disables Helix console-log scanning.

## Error Details

Every `Debug PALTests` leg of `runtime-coreclr outerloop` (definition 108) fails at the `Send job to Helix (Unix)` step. The Helix SDK's `AzurePipelines.props` cannot find `SYSTEM_ACCESSTOKEN`, so `paltests.proj` never sends the Helix job and the leg errors out before any test runs:

```
/__w/1/s/.packages/microsoft.dotnet.helix.sdk/11.0.0-beta.26411.119/tools/azure-pipelines/AzurePipelines.props(41,5): error : Azure Pipelines SYSTEM_ACCESSTOKEN variable not found. Either the build is not running in Azure Pipelines, or the current step is not configured correctly. Please configure this step with the System.AccessToken variable ... [/__w/1/s/src/coreclr/scripts/paltests.proj]
```

The failure is persistent: it reproduces across the entire scanned build window (builds 1560135, 1559609, 1558864, 1556858 all show it) and in the follow-up build 1560451, affecting all PALTests architectures. True origin likely predates the scanned window.

## Error Message

```json
{
"ErrorMessage": [
"error : Azure Pipelines SYSTEM_ACCESSTOKEN variable not found.",
"paltests.proj]"
],
"ErrorPattern": "",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

Agentic workflow metadata (ci-failure-scan)

Workflow artifact: ci-failure-scan
Artifact kind: kbe-verification
Verified match count: 2 hits in failure.log

---
Filed by [`ci-failure-scan`](https://github.com/dotnet/runtime/blob/main/.github/workflows/ci-failure-scan.md) (detection only). [`ci-failure-fix`](https://github.com/dotnet/runtime/blob/main/.github/workflows/ci-failure-fix.md) walks open `[ci-scan]` KBEs and either opens a small fix PR or comments here to loop in owners — it never disables the test.

> Generated by [CI Outer-Loop Failure Scanner](https://github.com/dotnet/runtime/actions/runs/32370639881) · opus48 · 496.5 AIC · ⌖ 18.1 AIC · ⊞ 20.7K · [◷](https://github.com/search?q=repo%3Adotnet%2Fruntime+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Fruntime%2Fci-failure-scan%22&type=issues)

### Report
|Build|Repository|Step Name|Console log|Pull Request|
|---|---|---|---|---|
|[1566089](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1566089)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1566089/logs/190)||
|[1565369](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1565369)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1565369/logs/205)||
|[1564675](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564675)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1564675/logs/202)|dotnet/runtime#131866|
|[1564549](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564549)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1564549/logs/205)||
|[1564131](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564131)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1564131/logs/197)||
|[1564048](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564048)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1564048/logs/182)||
|[1563902](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563902)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1563902/logs/187)||
|[1563824](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563824)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1563824/logs/178)||
|[1563695](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563695)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1563695/logs/1093)||
|[1563509](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563509)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1563509/logs/177)||
|[1563323](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563323)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1563323/logs/185)||
|[1562816](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1562816)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1562816/logs/490)||
|[1561949](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1561949)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1561949/logs/195)||
|[1561604](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1561604)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1561604/logs/1080)||
|[1561111](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1561111)|dotnet/runtime|Send job to Helix (Unix)|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1561111/logs/606)||
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|15|

Start with src/coreclr/scripts/paltests.proj and the runtime-coreclr outerloop definition 108, focusing on the Send job to Helix (Unix) step. Compare its configuration with the SYSTEM_ACCESSTOKEN requirement reported by .packages/microsoft.dotnet.helix.sdk/11.0.0-beta.26411.119/tools/azure-pipelines/AzurePipelines.props. Done means the PALTests legs submit jobs to Helix and proceed to test execution without the missing-variable error.

Written by the indexing model from the issue text.