validate: Use crossplane:stable as the default image

[adamwg]

Description of your changes

Now that the CLI version has diverged from the Crossplane core version, we can't assume there will always be a core Crossplane image with the CLI's version number. Use the stable tag, which gets updated with each release, as the default Crossplane image for validate so that we always point at the latest. Users can still select a different version using the --crossplane-image flag.

Fixes #145

I have:

• Read and followed Crossplane's contribution process.
• Run ./nix.sh flake check to ensure this PR is ready for review.
  - [ ] Added or updated unit tests.
  - [ ] Linked a PR or a docs tracking issue to document this change.
• Added backport release-x.y labels to auto-backport this PR.

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📥 Commits

Reviewing files that changed from the base of the PR and between f0d8480 and 65c41bc.

📒 Files selected for processing (1)

• cmd/crossplane/validate/cmd.go

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📝 Walkthrough

Walkthrough

The validate command now uses a fixed default Crossplane image from the CLI flag definition. The runtime fallback that constructed an image tag from the current version was removed.

Changes

Validate command image defaulting

Layer / File(s)	Summary
CLI default and run path cmd/crossplane/validate/cmd.go	CrossplaneImage now defaults to xpkg.crossplane.io/crossplane/crossplane:stable, and Run no longer assigns a version-derived image when the field is empty. The unused fmt and version imports were removed.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Breaking Changes	❌ Error	validate no longer derives the default Crossplane image from the CLI version, changing public command behavior under the cmd/** breaking-change policy.	Add the breaking-change label, or preserve the prior version-derived default behavior if this change should stay non-breaking.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is descriptive and accurately summarizes the change to the validate default image.
Description check	✅ Passed	The description is clearly related to the PR and explains why the default image is changing.
Linked Issues check	✅ Passed	The change addresses #145 by defaulting validate to xpkg.crossplane.io/crossplane/crossplane:stable and still allowing overrides.
Out of Scope Changes check	✅ Passed	The diff appears focused on the validate image default and contains no unrelated code changes.
Feature Gate Requirement	✅ Passed	PASS: The PR only changes validate's default image and removes runtime version fallback; it doesn't add apis/** changes or any new experimental feature requiring a gate.

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[jbw976]

this looks reasonable since we've now diverged versions and it looks like it correctly points to the most current stable image:

❯ docker run --rm xpkg.crossplane.io/crossplane/crossplane:stable --version
v2.3.3

[github-actions]

Successfully created backport PR for release-2.4:

• [Backport release-2.4] validate: Use crossplane:stable as the default image #149