Build: Skip the canary PR body update when the description has no markers

[TheSeydiCharyyev]

Closes #36195

What I did

applyCanaryPrBodyUpdate called replaceMarker for both canary markers, and replaceMarker throws when a pair is missing. So a PR whose description dropped the template published its packages fine and then lost the Update Canary PR Body job to expected 1 CANARY_RELEASE_HEADING pair, found 0. No install commands on the PR, red job, nothing saying why.

Now a missing pair is skipped and logged, and the PATCH is only sent if the body actually changed. replaceMarker still throws, because replace-pr-body-markers.ts is a CLI where a missing marker really is a mistake — the tolerance sits at the call site. To do that without duplicating the regex I pulled it into markerPattern and exported countMarkerPairs. replaceMarker behaves the same, error message included.

Second change: the failure comment now goes out before the body patch. On action: 'failed' the throw used to land first, so the comment telling the actor their canary failed never went out either. Same signal lost twice.

I kept this PR on the template, markers and all, so a canary here still works.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Six cases in update-canary-pr-body-from-run.test.ts: missingCanaryMarkers naming what a description lacks, the same for a marker that appears twice, applyCanaryPrBodyUpdate leaving such a description alone, the failure path still commenting and skipping the PATCH, the release path skipping it too, and the comment landing before the patch.

Each one was checked by breaking the source, not just by passing. Putting the strict replaceMarker back fails the three marker cases and leaves the two older applyCanaryPrBodyUpdate tests green. Moving the comment back after the patch fails only the ordering case.

Worth flagging: nothing in CI runs these tests. They are not in vitest.config.ts projects, they use node:test rather than vitest, and no workflow calls them. I ran them with node --test, which needs the .nvmrc Node or newer for type stripping. I can wire them into CI, here or in a separate PR.

Manual testing

1. node --test .github/scripts/update-canary-pr-body-from-run.test.ts with the Node version from .nvmrc. 21 tests, all passing.
2. For the real path, take a PR whose description has no CANARY_RELEASE_HEADING or CANARY_RELEASE_SECTION pair — Preview: Respect prefers-reduced-motion when scrolling to an anchor #36155 is one — and publish a canary for it with Run workflow and the pr input.
3. Before this change the Update Canary PR Body job fails with expected 1 CANARY_RELEASE_HEADING pair, found 0. After it the job passes and logs PR #36155 does not have exactly one CANARY_RELEASE_HEADING or CANARY_RELEASE_SECTION pair, leaving that part of the body, and the description is left as the author wrote it.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

🦋 Canary Release - 🚢 Released b7bbec5

This pull request has been released as canary packages. Try it out in a new project or update an existing project with the commands below.

# For a new project
npx --yes --allow-remote=all https://pkg.pr.new/create-storybook@b7bbec5

# or for an existing project
npx --yes --allow-remote=all https://pkg.pr.new/storybook@b7bbec5 upgrade

[coderabbitai]

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📒 Files selected for processing (2)

• .github/scripts/update-canary-pr-body-from-run.test.ts
• .github/scripts/update-canary-pr-body-from-run.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• .github/scripts/update-canary-pr-body-from-run.test.ts

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---

Walkthrough

The canary update flow now validates marker pairs before replacement. Missing or duplicate markers no longer abort updates. Failure comments are posted before body updates, and unchanged bodies skip PATCH requests.

Changes

Canary PR body updates

Layer / File(s)	Summary
Marker pair validation .github/scripts/replace-pr-body-markers.ts	The marker pattern is shared through markerPattern. The exported countMarkerPairs counts marker pairs. replaceMarker now requires exactly one pair.
Safe canary replacement .github/scripts/replace-pr-body-markers.ts, .github/scripts/update-canary-pr-body-from-run.ts, .github/scripts/update-canary-pr-body-from-run.test.ts	missingCanaryMarkers identifies invalid marker pairs. Canary body updates leave descriptions unchanged when markers are missing or duplicated. Tests cover these cases.
Failure notification ordering .github/scripts/update-canary-pr-body-from-run.ts, .github/scripts/update-canary-pr-body-from-run.test.ts	Failure comments are posted before body updates. The PATCH is skipped when markers are invalid or the body is unchanged. Tests verify command ordering and skipped calls.

Sequence Diagram(s)

sequenceDiagram
  participant CanaryRun
  participant GitHubComment
  participant GitHubPullRequest
  CanaryRun->>GitHubComment: Post failure comment
  CanaryRun->>GitHubPullRequest: Fetch PR body
  CanaryRun->>GitHubPullRequest: PATCH only when the body changes

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Merge Risk: 🔵 Low · up to 97fd8

Canary PR updates now avoid failing on absent markers and avoid unnecessary body patches, but malformed marker delimiters may still permit an incorrect PR-body update. This is a bounded workflow risk that should be addressed before relying on malformed templates.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

---

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Actionable comments posted: 2

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Inline comments:
In @.github/scripts/replace-pr-body-markers.ts:
- Line 14: Update countMarkerPairs to validate that the body contains exactly
two marker delimiters, rejecting odd or otherwise unpaired counts instead of
counting only the first global pair. Ensure replaceMarker and
missingCanaryMarkers preserve this rejection behavior, and add a regression test
covering a body with three delimiters.

In @.github/scripts/update-canary-pr-body-from-run.ts:
- Line 225: Update the diagnostic in the missingCanaryMarkers handling to state
that PR #${pr} does not have exactly one marker pair, covering both missing and
duplicate pairs; preserve the existing marker list and skipped-body-update
behavior.

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Configuration used: Organization UI

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📒 Files selected for processing (3)

• .github/scripts/replace-pr-body-markers.ts
• .github/scripts/update-canary-pr-body-from-run.test.ts
• .github/scripts/update-canary-pr-body-from-run.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

[JReinhold]

Feedback: I had to read the issue and PR description 4 times to fully understand what the problem was, and what the fix actually meant for user facing changes.

I think this change can be summarised to: "Before, when canaries failed because the PR body didn't follow the template, nothing would happen. Now, it correctly results in a 'canary failed' comment on the PR."

If I'm right, it would have made my review a lot easier if it was written somewhere. If I'm wrong, please correct me.

[TheSeydiCharyyev]

You're half right, and the half that's off is the main one.

Two separate things were broken.

1. Canary succeeds, PR description has no markers. Packages publish to pkg.pr.new fine, then Update Canary PR Body dies on expected 1 CANARY_RELEASE_HEADING pair, found 0. Red job, and the install commands never reach the PR. This was the common case and the one the issue was about.

2. Canary fails, PR description has no markers. The same throw landed before gh pr comment, so the "canary failed" notice never went out either.

Your summary is case 2. In case 1 nothing failed from the user's side — the canary existed, only the links didn't arrive.

On the description: fair. One line at the top would have done it — "a PR whose description dropped the template used to break the canary body update; now that part is skipped and logged".