Summary · Handing off to Kubernetes

Key takeaways

The construct → compose boundary in the academy story Crossplane composes, Sandcastle constructs, Picos behave is a Git branch on a durable target repository — nothing more.
The concrete hand-off from the Hello World Pico Sandcastle lab to the Hello Pico on Kubernetes lab is a single field promotion: value from rules/hello.yaml on the Sandcastle branch becomes spec.value on an XHelloWorldPico Composite Resource.
A well-behaved hand-off is read-only against the Sandcastle side, deterministic against the branch, byte-equivalent to the downstream contract, and cluster-independent.
Cluster-side reconciliation belongs to the Kubernetes lab, not to the hand-off. Keeping that separation is what makes the hand-off reusable across future compositions.
The runnable Sandcastle → Kubernetes hand-off lab enforces all four rules with an automatable verify.sh and produces an XR that drops into the Kubernetes lab without modification.

The rest of Part 3 will develop the surrounding outer delivery loop (branch → PR → merge → GitOps → Crossplane reconciliation) and the guardrails that live outside the Sandcastle’s boundary. See Part 3 for the scaffolded outline.
Downstream cluster verification of the composed artifact continues to live in labs/hello-pico-on-kubernetes/, and the Sandcastle side that produces the branch continues to live in labs/hello-world-pico-sandcastle/.
Multi-rule / multi-artifact hand-off, and GitOps-based promotion, are natural extensions for a later Part 3 lesson.

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