[AI discovered CI] ApiCompat and GenAPI integration tests cannot resolve .NET 11 targeting packs

## Build Information
- **Current build:** [1575657](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1575657)
- **Branch:** `refs/heads/main`
- **Failing tests:** ApiCompat and GenAPI integration tests in Windows x64 / Windows x64 FullFramework Helix jobs (13 tests).
- **Phase:** `test-execution`; **failureType:** `test-assertion`; **evidenceSources:** `helix-trx`
- **Matching prior builds:** None in the supplied related-failure summaries. Recent sequence: failed 1575533, 1575141, 1575045, 1574612, 1573708, 1573623, 1573087, 1571869, 1571595, 1571404; passed 1575340, 1573721, 1573234, 1572955, 1572757, 1572554, 1571833, 1571770, 1571202.
- **Failure fingerprint:** `test-execution|test-assertion|microsoft.dotnet.apicompat.task.integrationtests.validateassembliestargetintegrationtests.validateassemblies_strictmode_failsonaddition|test-method-microsoft.dotnet.apicompat.task.integrationtests.validateassembliestargetintegrationtests.validateassemblies_strictmode_failsonaddition-threw-exception-fluentassertions`

## Failure History
The current build reports 13 tests failing through the same downstream command-pass assertion. The supplied history does not establish recurrence of this exact NU1100 mechanism in an independent build; the surrounding builds are mixed pass/fail observations.

## Error Details
```text
Failed to load prune package data from PrunePackageData folder, loading from targeting packs instead
: error NU1100: Unable to resolve 'Microsoft.NETCore.App.Ref (= 11.0.0-preview.7.26381.103)' for 'net11.0'.
: error NU1100: Unable to resolve 'Microsoft.WindowsDesktop.App.Ref (= 11.0.0-preview.7.26381.103)' for 'net11.0'.
: error NU1100: Unable to resolve 'Microsoft.AspNetCore.App.Ref (= 11.0.0-preview.7.26381.103)' for 'net11.0'.
Failed to restore .
```

## Root Cause Analysis
**Observed:** Independent ApiCompat and GenAPI setup commands fail before exercising product behavior because .NET 11 reference packs cannot be resolved.

**Assessment:** The immediate shared mechanism is unavailable or unresolved targeting-pack version `11.0.0-preview.7.26381.103`; the named test assertions are downstream wrappers. The evidence does not establish whether this is SDK test-layout, package publication, or environment configuration.

**Confidence:** Medium.

**Alternatives / Unknowns:** No source configuration, binlog, target-branch comparison, or matching related candidate was supplied. A broad feed/Helix provisioning outage may belong in `dotnet/dnceng` rather than this repository.

## Suggested Investigation
Inspect the failing Helix test layout and restore sources first, then compare with the last passing build and verify publication/reachability of all three exact reference-pack versions. Use restore diagnostics/binlogs to distinguish SDK test setup from external feed or provisioning failure.

> Generated by [🕵️ CI Quality Investigator](https://github.com/dotnet/sdk/actions/runs/33452127743) · gpt56 · 3.48 AIC · ⌖ 0.749 AIC · ⊞ 17.5K · [◷](https://github.com/search?q=repo%3Adotnet%2Fsdk+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Fsdk%2Fci-quality-monitor%22&type=issues)