fix(cluster): add bounds check for workerGroupSpecs array access

[laurafitzgerald]

Fixes: RHOAIENG-54729
Made-with: Cursor

Issue link

https://redhat.atlassian.net/browse/RHOAIENG-54729

What changes have been made

Add defensive bounds checking before accessing workerGroupSpecs[0] in three functions to prevent IndexError on head-only Ray clusters (num_workers=0).
Head-only clusters have an empty workerGroupSpecs list, which caused crashes when calling status(), list_all_clusters(), or get_cluster(). The fix guards all three access points and defaults worker-related values to 0 when no worker groups are defined.
Functions fixed:

• _head_worker_extended_resources_from_rc_dict() — returns empty worker resources dict
• get_cluster() — defaults worker CPU/memory limits/requests to 0
• _map_to_ray_cluster() — defaults worker specs to 0

Verification steps

1. Run the unit tests:

   poetry run pytest src/codeflare_sdk/ray/cluster/test_cluster.py -v
   

2. The new test_head_only_cluster_no_workers test validates all three code paths with an empty workerGroupSpecs list.
3. Manual verification (requires KubeRay operator):
   • Create a RayCluster with num_workers=0 (empty workerGroupSpecs)
   • Call cluster.status(), list_all_clusters(), and cluster.details()
   • Confirm no IndexError; results show num_workers=0

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • Testing is not required for this change

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.32%. Comparing base (d87aac4) to head (4c05c43).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1041      +/-   ##
==========================================
+ Coverage   96.15%   96.32%   +0.17%     
==========================================
  Files          23       23              
  Lines        2238     2261      +23     
==========================================
+ Hits         2152     2178      +26     
+ Misses         86       83       -3     

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[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pawelpaszki

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