feat(synthetics): add enum value for Synthetics Canary NodeJS 3.1 runtime

[bilalq]

Issue # (if applicable)

N/A

Reason for this change

This was previously missing from the runtime enum. The older version doesn't have types available on npm, so it's difficult and awkward to use.

Description of changes

This change just adds an enum value for the newer version of the runtime. See docs at:
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Library_Nodejs.html#CloudWatch_Synthetics_runtimeversion-syn-nodejs-3.1

Describe any new or updated permissions being added

N/A

Description of how you validated changes

The documentation was reviewed and the code was checked to be consistent with pre-existing enum values.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[aws-cdk-automation]

(This review is outdated)

[Copilot]

Pull request overview

Adds support for the CloudWatch Synthetics syn-nodejs-3.1 canary runtime by exposing it as a Runtime constant in aws-synthetics, making it easier for CDK consumers to select the newer Node.js runtime.

Changes:

• Add Runtime.SYNTHETICS_NODEJS_3_1 mapped to syn-nodejs-3.1.
• Document the runtime’s Node.js version and notable features with an AWS docs reference.

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[bilalq]

Exemption Request:

This PR only adds a new enum value. The autogenerated documentation should be sufficient. The last PR that added a new enum value here also had no readme or test changes. See: #36652

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-03-19 10:38 UTC · Rule: default-squash
• ✅ Checks passed · in-place
• ✅ Merged — 2026-03-19 11:19 UTC · at 2e3024ede71550b9ba7b0f544964c66723b58a4e

This pull request spent 40 minutes 22 seconds in the queue, including 40 minutes 10 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • feat(synthetics): add enum value for Synthetics Canary NodeJS 3.1 runtime #37282
• #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
  • feat(synthetics): add enum value for Synthetics Canary NodeJS 3.1 runtime #37282
• any of [🛡 GitHub branch protection]:
  • check-success = validate-pr
  • check-neutral = validate-pr
  • check-skipped = validate-pr
• any of [🛡 GitHub branch protection]:
  • check-success = build
  • check-neutral = build
  • check-skipped = build

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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