Error handling

[magicmark]

This PR refactors the schema coordinate resolution logic and introduces explicit error handling as proposed by @benjie.

• Split the previous monolithic resolveASTSchemaCoordinate function into multiple specialized resolveTypeCoordinate, resolveMemberCoordinate, etc... functions.
• Introduce explicit error throwing for missing schema elements on parent schema coordinate nodes per the updated spec

[Copilot]

Pull Request Overview

This PR refactors the schema coordinate resolution logic and introduces explicit error handling as proposed by Benjie.

• Split the previous monolithic resolver into multiple specialized functions.
• Introduce explicit error throwing for missing schema elements in certain coordinate types.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/utilities/resolveSchemaCoordinate.ts	Refactored coordinate resolution into multiple functions with explicit error handling for missing directives, types, and members.
src/utilities/tests/resolveSchemaCoordinate-test.ts	Updated tests to expect thrown errors for specific error scenarios.

Comments suppressed due to low confidence (2)

src/utilities/resolveSchemaCoordinate.ts:115

• Consider making the error handling behavior consistent; for instance, throwing an error when a directive is missing (as done in directive argument resolution) might provide clearer feedback than returning undefined.

if (!directive) { return; }

src/utilities/resolveSchemaCoordinate.ts:235

• The error message for non-object/interface types in member coordinate resolution may be ambiguous; consider specifying that the coordinate is only applicable to Object or Interface types to help diagnose the issue more clearly.

throw new Error(`Expected ${inspect(typeName)} to be defined as a type in the schema.`);

[Copilot]

Add documentation and tests to clearly define the expected behavior when a member name does not exist, ensuring that the resolver's behavior is well-specified for these edge cases.

[benjie]

Some of the errors are a little misleading, I've posted suggestions