test: verify PR output remains immutable

[k11kirky]

Problem

The PR output utility should remain a pure transformation so callers can safely reuse their existing output objects.

Changes

Add a regression test confirming buildPrOutput does not mutate its input.

How did you test this?

• git diff --check
• Automated test not run: repository dependencies are not installed, so biome and vitest are unavailable.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 682170e.}

[posthog]

👋 Visual changes detected for this PR.

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If these changes are unexpected, they may be caused by a flaky test or a broken snapshot on master. Don't approve — rerun the job or wait for a fix.

[charlesvien]

Hey @k11kirky, we've migrated this repo into the PostHog/posthog monorepo, so this PR needs to be recreated there.

Easiest path: check out the monorepo and run the /porting-code-prs skill with your agent pointed at this PR. It has the migration guide and path remappings baked in so the agent doesn't have to figure them out. You don't strictly need it though, just asking your agent to port the PR works fine too.

Shout if you get stuck.