Submission Checklist

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Please take the following actions before submitting this pull request.

• Fork your PR branch from the Toolkit "develop" branch (not main)
• Test all changes with pre-commit in a local branch #
• Confirm that "make tests" passes all tests
• Add or modify unit tests to cover code changes
• Ensure that unit test coverage remains above 80%
• Update all applicable documentation
• Follow Cluster Toolkit Contribution guidelines #

What this change does

This change adds an early check (pre-validation) to make sure there's enough space (capacity) in a specific machine reservation before we try to create the cluster's nodes.

Why this is important

Right now, if you ask for more machines than are available in a reservation, the cluster setup process only fails much later, when it tries to actually create those machines. This is a problem because:

• It wastes time and computing power trying to get machines that aren't there.
• You don't find out about the capacity problem right away.

How it was implemented

I added a new section of code to the google_container_node_pool resource block to implement robust validation for reservation affinity. This involved creating two new precondition blocks. One to ensure a single reservation is specified when required, and another to verify that the requested node count does not exceed the available capacity of that reservation.