fix(ec2): vpc interface endpoint not attaching to selected subnets (#…

[Aaxhirrr]

fix(ec2): vpc interface endpoint not attaching to selected subnets (#37144)

CfnSubnet objects passed within SubnetSelection are now automatically wrapped with Subnet.fromSubnetAttributes to ensure they can be used for things like interface endpoint SubnetIds.

Issue # (if applicable)

Closes #37144

Reason for this change

When creating a VPC interface endpoint and passing CfnSubnet objects directly into the subnets array of SubnetSelection, the generated CloudFormation template results in an empty SubnetIds array. This is because CfnSubnet is an L1 construct and does not implement the full ISubnet interface, specifically lacking the .subnetId property that the endpoint selection logic relies on, causing it to fail silently.

Description of changes

• Updated Vpc.selectSubnetObjects in @aws-cdk/aws-ec2 to intercept SubnetSelection.subnets arrays.
• It now checks if any explicitly provided subnets are instances of CfnSubnet.
• If found, it automatically wraps them in a singleton wrapper using Subnet.fromSubnetAttributes(this, id, { subnetId: s.ref, ... }), retaining their availability zone and CIDR block properties if available.
• This allows vpc-endpoint constructs (and anything else utilizing selectSubnetObjects) to extract the proper routing IDs during CloudFormation synthesis.

Describe any new or updated permissions being added

N/A - No new permissions or IAM updates are required for this construct logical fix.

Description of how you validated changes

• Added a new unit test endpoint selection works with L1 CfnSubnet passed as ISubnet in packages/aws-cdk-lib/aws-ec2/test/vpc-endpoint.test.ts.
• The test explicitly verifies that passing a CfnSubnet to vpc.addInterfaceEndpoint() properly populates the SubnetIds property with the Ref of the CloudFormation subnet in the synthesized output.

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

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