Type generation crashes when encountering external type references

[GSGerritsen]

Environment

Node: 22.15.0
capnp-es version: 0.0.11

Reproduction

1. Create a Cap'n Proto schema that imports types from an external schema
2. Compile only the importing schema without including the external schema
3. The compiler crashes with "missing node" error

Describe the bug

The TypeScript code generator throws an error when it encounters references to external types that aren't available in the current compilation context. This happens when a Cap'n Proto schema imports types from other schemas that aren't being compiled in the same invocation.

When the compiler encounters an external type reference (struct, enum, or interface) that isn't in the current node context, it throws an error in lookupNode() with message: "missing node".

Additional context

No response

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