The Release Stage 1 workflow was failing with the error "GraphQL: Base branch was modified. Review and try the merge again" due to a race condition when multiple dependency update bots tried to merge PRs simultaneously.

Problem

The workflow used a matrix strategy that ran alpha, beta, and stable dependency update jobs in parallel:

strategy:
  matrix: ${{ fromJson(needs.determine-release-types.outputs.matrix) }}

This caused race conditions where:

1. All three jobs (alpha, beta, stable) would run simultaneously
2. Each would create PRs and attempt to auto-merge them at the same time
3. When one job merged its PR (modifying the base branch), other jobs would fail with "Base branch was modified"
4. This resulted in workflow failures like run #17525831245

Solution

Added a simple max-parallel: 1 constraint to the existing matrix strategy:

strategy:
  max-parallel: 1
  matrix: ${{ fromJson(needs.determine-release-types.outputs.matrix) }}

Key improvements:

• ✅ Minimal change - Only one line added to the existing workflow
• ✅ Preserves matrix structure - Maintains clean DRY approach without code duplication
• ✅ Prevents race conditions - Ensures sequential execution by allowing only one matrix job to run at a time
• ✅ Easy to understand - Clear intent and simple implementation
• ✅ Maintains existing logic - All matrix variables and conditional execution preserved

Benefits over Sequential Jobs Approach

This solution is superior to creating separate sequential jobs because it:

• Keeps the clean matrix structure intact
• Avoids duplicating job definitions
• Maintains all existing matrix variables (${{ matrix.release_type }}, ${{ matrix.config_file }})
• Requires minimal changes to the existing workflow
• Is easier to understand and maintain

Testing

Added comprehensive test suite (test/test-race-condition-fix.sh) that validates:

• YAML syntax correctness
• Matrix strategy with max-parallel constraint
• Single job structure (not separate sequential jobs)
• Matrix variable usage preservation
• Proper race condition prevention

All existing tests continue to pass, ensuring no regressions were introduced.

Fixes #227.

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