feat: @oneOf typed blueprint definitions with SuperCase node type keys

[pyramation]

Summary

Adds infrastructure for generating fully-typed GraphQL @oneOf input types for blueprint definitions, using SuperCase node type names (e.g., DataTimestamps, AuthzEntityMembership) as discriminant keys. This enables SDK autocomplete and compile-time validation for blueprint parameters.

Three layers of changes:

1. PostGraphile plugin (graphile-settings/src/plugins/blueprint-types/): A factory that accepts NodeTypeRegistryEntry[] and generates a type hierarchy:

   • Per-node-type params inputs (e.g., DataTimestampsParams) derived from parameter_schema via JSON Schema → GraphQL conversion
   • BlueprintNodeInput @oneOf — discriminated union of all non-relation node types + shorthand: String
   • BlueprintRelationInput @oneOf — discriminated union of relation node types
   • BlueprintTableInput and BlueprintDefinitionInput wrapping types

2. Codegen (graphql/codegen/, graphql/query/): Detects isOneOf on INPUT_OBJECT types from introspection and generates TypeScript discriminated unions instead of interfaces:

   // Generated output for @oneOf types:
   export type BlueprintNodeInput =
     | { shorthand: string }
     | { DataId: DataIdParams }
     | { DataTimestamps: DataTimestampsParams };

3. Introspection: Adds isOneOf field to the schema introspection query and propagates it through the type registry transform pipeline.

Note: The plugin is exported but not yet wired into the production schema build — it requires a caller to query node_type_registry at build time and pass the entries to createBlueprintTypesPlugin(). This is a deliberate separation; wiring happens in a follow-up.

Review & Testing Checklist for Human

• Verify isOneOf introspection compatibility: The introspection query now requests isOneOf on all types. Confirm your GraphQL server (PostGraphile v5 / graphql-js version) supports this field — if not, introspection queries may fail or return errors for non-__Type fields. Test by running the introspection query against a live endpoint.
• Review as GraphQLInputType casts in plugin.ts (lines 288, 315, 340, 385-390): build.getTypeByName() returns GraphQLNamedType and we cast to GraphQLInputType. If a type name ever collides with a non-input type, this would cause a runtime error. Verify this is safe given the plugin-controlled naming (*Params, Blueprint*Input).
• Empty params placeholder UX: Node types with no parameter_schema properties get a _: Boolean placeholder field, meaning SDK users would write { DataId: { _: true } }. Evaluate whether this is the desired DX vs. allowing empty objects.
• Run pnpm build at repo root to confirm all packages compile cleanly with the new isOneOf additions across graphql/query, graphql/codegen, and graphile/graphile-settings.
• End-to-end test plan: After wiring the plugin into the production preset, run codegen against a live schema and verify the generated TypeScript types show correct discriminated unions with SuperCase keys matching node_type_registry entries.

Notes

• The BuildLike interface in json-schema-to-graphql.ts uses any for GraphQLNonNull/GraphQLList constructor params to work around graphql-js type variance. This is intentional — the alternative is duplicating graphql-js's internal generic constraints.
• isOneOf is added to the ResolvedType interface in both graphql/query and graphql/codegen packages (they share the same interface shape but are separate files).

Link to Devin session: https://app.devin.ai/sessions/5d550def7a314c97854ec12fa09dd4ca
Requested by: @pyramation

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