[seshubaws]

Issue #, if available

Description of changes

Sets UpdateReplacePolicy: Retain on the generated AWS::Lambda::WebFunctionRevision, for both AutoDeploymentMode values. The endpoint, function and role are unchanged.

Every revision property is create-only, so each code or configuration change replaces <LogicalId>Revision. With AutoDeploymentMode: Disabled, the endpoint usually still routes to the old revision through RevisionWeights. CloudFormation's cleanup then fails to delete it ("cannot be deleted because the endpoints [prod] are using it") and retries for about 10 minutes before finishing with "One or more resources could not be deleted". With Retain, CloudFormation skips that delete.

• An UpdateReplacePolicy set on the AWS::Serverless::WebFunction still applies to every generated resource and overrides this default.
• Replaced revisions are no longer tracked by the stack. Deleting the stack deletes the function, which deletes all of its revisions.

Description of how you validated changes

• Transform tests: updated the WebFunction outputs, and added webfunction_update_replace_policy for the override.
• make format-check, make lint and make test pass.
• Deployed templates transformed with this branch, in us-east-2:
  • LatestRevision update: the endpoint moved to the new revision, and the old one was DELETE_SKIPPED (37s).
  • Disabled update with the endpoint pinned to the old revision: DELETE_SKIPPED, then UPDATE_COMPLETE in 38s with no warning (previously about 10 minutes and "could not be deleted").
  • Failed update with rollback: the endpoint's weights and WebFnRevision were restored. The revision created by the failed update was also DELETE_SKIPPED, because UpdateReplacePolicy applies to rollback cleanup too.
  • Stack deletion: completed in 32s, and the function and all 4 revisions were deleted.

Checklist

• Review the generative AI contribution guidelines
• Adheres to the development guidelines
• Add/update transform tests
  • Using correct values
  • Using wrong values
• Add/update integration tests

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