ci: don't allow breaking changes in PR commit messages

[jamietanna]

Changes

Renovate 44.0.0 was incorrectly released from #44004 due to the
BREAKING ... reference in the commit message.

Renovate uses Squash Merge as our method for merging commits into
main, and when enabled with the Merge Queue[0], this doesn't provide
maintainers with the ability to inspect the commit messages before
merging (which would be the case if not using the Merge Queue, we would
likely rewrite the commit message prior to merge.

With this in mind, Renovate maintainers often don't inspect the commit
messages, allowing them to stay as they are, as they'll be squashed into
the final commit.

In the case of #44004, this led to us missing the BREAKING ...
trailing message - from changes that were split into #44939 - and
because of this, semantic-release published this as a major release.

As a means to prevent this happening again, we can introduce a CI check
that validates - with the same underlying library as semantic-release -
whether a major release is being suggested, and if so, rejecting it.

Tested with: https://github.com/renovatebot/renovate/actions/runs/30455613636/job/90588296364#step:4:136

Context

Please select one of the following:

• This closes an existing Issue, Closes: #
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

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Documentation (please check one with an [x])

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I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests, but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository:

[Copilot]

Pull request overview

This PR adds a CI safeguard to prevent accidental major releases caused by breaking-change markers in PR commit messages, by running an offline semantic-release dry-run against the post-merge state and failing if it would produce a major bump.

Changes:

• Introduces a semantic-release dry-run helper script (tools/check-release-dry-run.ts) that computes whether the next release would be major.
• Adds a small Vitest suite to validate the “major vs non-major vs no-release” evaluation logic.
• Extends the existing check-commit-messages workflow with a new dry-run-major job that runs the dry-run after checkout and fails the PR if a major bump is detected.

Review notes (actionable):

• The workflow currently runs node tools/check-release-dry-run.ts .... Unless the CI environment is explicitly set up to execute TypeScript files (loader like tsx/ts-node, etc.), this is likely to fail because Node does not generally execute .ts directly. The workflow should invoke the script using the repo’s standard TS execution mechanism (e.g., pnpm exec tsx ... or an equivalent established pattern in this repo).
• In evaluateResult, the “no release” branch discards any available lastRelease.version when nextRelease is missing/null. Keeping lastVersion even when willRelease is false would improve diagnostics and makes the helper more accurate for partial/edge result shapes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tools/check-release-dry-run.ts	Adds a programmatic semantic-release dry-run and major-release detection logic intended for CI gating.
tools/check-release-dry-run.spec.ts	Adds unit tests for evaluateResult to ensure major/premajor detection and no-release handling.
.github/workflows/check-commit-messages.yml	Adds a new CI job to run the dry-run on PR merge state and fail if it would trigger a major release.

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[github-actions]

🎉 This PR is included in version 44.1.0 🎉

The release is available on:

• GitHub release
• 44.1.0

Your semantic-release bot 📦🚀