Cutting the ceremony: @McpDomain on classes
Every @McpDomain SPI in the platform follows the same three-file pattern: an interface in platform-api, a default implementation in the runtime module, and generated REST + GraphQL endpoints from the APT. For domains with a single implementation and no alternative providers, the interface-and-default split is pure ceremony — files without value.
I wanted to let @McpDomain go directly on a concrete class. The annotation was already @Target(TYPE), so it could be placed on classes today — the scanners just refused to look at them. Four independent scanners each had their own interface-only gate, all checking the same thing in slightly different ways.
The fix turned out to be satisfyingly mechanical. Remove the isInterface check in McpDomainJandexScanner (which feeds all three Spring generators), lift the same gate in both scan paths of GraphQLResolverProcessor (the Jandex path and the RoundEnvironment path), and teach GraphQLModelScanner to read @PlatformQuery/@PlatformMutation directly from class methods when it encounters a @McpDomain class without @GraphQLApi.
The one thing that wasn’t obvious: the runtime scanner’s computeIfAbsent ordering. I’d moved the domain initialization before the hasGraphQLApi check — seemed like a harmless scoping change to make the variable available in both branches. Claude caught it during review: ModelEnricher beans would now create empty domain entries in the first pass, and the second pass’s if (domainOps.containsKey(domain)) { continue; } guard would skip registering the real operations from the interface. The fix was straightforward — call computeIfAbsent inside each branch that actually adds operations, not unconditionally at the top.
I also added a compile-time courtesy: the APT now emits a WARNING when @McpDomain is placed on a class without a visible CDI scope annotation. It can’t see inherited scopes or stereotypes, so it’s best-effort — CDI injection failure at runtime remains the real gate. But it catches the common case where someone simply forgot @ApplicationScoped.
The DomainScanResult record got a rename along the way — spiInterfaceFqcn/spiInterfaceSimple became sourceFqcn/sourceSimple with an isInterface flag. The old names were actively misleading when the source was a class.
What this opens up: every domain across the casehub ecosystem that has exactly one implementation — simple CRUD services, dashboard queries, utility endpoints like GDPR erasure — can drop the interface-and-default wrapper. The issue already lists the candidates; the migration is a separate pass.