Reference CloudFormation-managed stacks (mixed estates)

You don't have to migrate a producer stack to reference it. When an Fn::ImportValue / Fn::GetStackOutput reference is not found in cdkd state, cdkd falls back to CloudFormation — ListExports for Fn::ImportValue (CFn's own semantic for the intrinsic), the stack's outputs via DescribeStacks for Fn::GetStackOutput — so a cdkd-deployed stack can consume values from a stack still managed by cdk deploy / raw CloudFormation, with zero changes on the producer side.

This makes the recommended split work out of the box: shared infrastructure (VPC, domains, IAM) stays on the CDK CLI, while dev/test app stacks iterate via cdkd.

// Producer: deployed with `cdk deploy` (stays CloudFormation-managed).
new cdk.CfnOutput(this, 'SharedVpcId', {
  value: vpc.vpcId,
  exportName: 'SharedVpcId',
});

// Consumer: deployed with `cdkd deploy`. Resolution order is cdkd state
// first, then CloudFormation — same syntax either way.
const vpcId = cdk.Fn.importValue('SharedVpcId');

How it behaves:

cdkd-first precedence. The fallback fires only after cdkd state misses, so cdkd-to-cdkd references are untouched and a name collision resolves to the cdkd export.
Weak reference. A CFn-sourced value is not recorded into cdkd state, and neither engine blocks deleting the CFn producer while cdkd consumers reference it (CloudFormation's export-in-use protection cannot see cdkd consumers). Check downstream consumers before deleting a producer.
IAM: the deploying credentials need cloudformation:ListExports / cloudformation:DescribeStacks for the fallback. Without them, cdkd warns and fails with the ordinary not-found error.
Opt-out: --no-cfn-fallback (on deploy / diff) pins cdkd-state-only resolution — minimal IAM, and an export-name typo fails fast instead of matching an unrelated CloudFormation export.
This also works mid-migration: after cdkd export hands a producer back to CloudFormation, remaining cdkd consumers keep resolving its outputs through the fallback (no leaf-first ordering requirement).

See cross-stack-references.md for the full design (resolution order, weak-vs-strong reference semantics, cross-region / cross-account forms).