clusterapi: set resource slice count for DRA scale-from-zero

[dlanov]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Cluster API scale-from-zero generates a synthetic ResourceSlice for node
groups configured with DRA capacity annotations.

The generated ResourcePool currently leaves ResourceSliceCount at its
zero value. The DRA allocator treats that pool as incomplete, so its devices
are ignored and DRA workloads cannot trigger scale-from-zero.

Set ResourceSliceCount to 1, matching the single ResourceSlice generated
for the synthetic node.

The existing TestAnnotations coverage is updated to verify the generated
resource slice contains the correct pool metadata.

Which issue(s) this PR fixes:

Fixes #10199

Special notes for your reviewer:

Verified that the updated test fails when the production change is removed:
the expected ResourceSliceCount is 1 while the generated value remains 0.

Validation:

go test -race -vet=all ./cloudprovider/clusterapi/...

The separate MIG device-attribute limitation mentioned in #10199 is outside
the scope of this change.

Does this PR introduce a user-facing change?

Fixed Cluster API DRA scale-from-zero by generating ResourceSlices with a valid resource slice count.

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📥 Commits

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📒 Files selected for processing (2)

• cluster-autoscaler/cloudprovider/clusterapi/clusterapi_unstructured.go
• cluster-autoscaler/cloudprovider/clusterapi/clusterapi_unstructured_test.go

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📝 Walkthrough

Walkthrough

The cluster API provider now sets ResourceSliceCount to 1 for generated GPU resource pools. TestAnnotations verifies the updated ResourcePool value.

Changes

DRA resource slice pool

Layer / File(s)	Summary
Set and validate the resource slice pool count cluster-autoscaler/cloudprovider/clusterapi/clusterapi_unstructured.go, cluster-autoscaler/cloudprovider/clusterapi/clusterapi_unstructured_test.go	Generated GPU resource slices set ResourceSliceCount to 1. TestAnnotations expects the same value.

Estimated code review effort: 2 (Simple) | ~5 minutes

Merge Risk: ⚪ Minimal · up to a5af0

This localized change sets the generated resource slice count to match the single slice produced for scale-from-zero, enabling DRA workloads to trigger node scaling; no actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: choraden

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes satisfy issue #10199 by setting ResourceSliceCount to 1 for the single synthetic ResourceSlice and updating TestAnnotations accordingly. The separate MIG device attribute limitation remain…
Out of Scope Changes check	✅ Passed	The pull request changes only the synthetic ResourcePool metadata and its corresponding test. No unrelated code changes are present.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: setting the DRA resource slice count for Cluster API scale-from-zero.

Full details: Linked Issues check

Explanation

The changes satisfy issue #10199 by setting ResourceSliceCount to 1 for the single synthetic ResourceSlice and updating TestAnnotations accordingly. The separate MIG device attribute limitation remains outside this issue's scope.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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