Sealed Coordinate component on ValidationError

ValidationError.coordinate is a nullable String whose grain consumers re-derive by dot-splitting. ValidationError.forType and forField know the grain at construction and collapse it to a string plus null for schema-wide, and then WatchErrorFormatter reconstructs it with isTypeLevel / typeOf predicates. A third fact about the same slot, that warnings carry no coordinate so a coordinate filter excludes them by construction, lives only as a comment in DiagnosticsTool. A sealed Coordinate { SchemaWide | TypeLevel | FieldLevel } component would make the grain a read slot instead of a parse, delete the formatter’s predicates, and turn the warnings invariant into a type fact.

Carved out of the aggregated-diagnostics MCP work at Spec review, which surfaced the lift but does not depend on it: with coordinate still a string, that item’s coordinate-reading dimensions do the dot-split in exactly one extractor, and one site is not the duplication this lift exists to remove.

Blast radius, measured at carve-out (re-measure at pickup): WatchErrorFormatter (the isTypeLevel / typeOf deletes), DiagnosticsTool’s filter comparison and wire `putIfNotNull, and six graphitron test files asserting on coordinate strings (GraphitronSchemaBuilderTest, ConditionCommandsPipelineTest, ConnectionTypeValidationTest, TenantScopeValidationTest, NodeIdPipelineTest, and the typed-rejection pipeline test). Spans graphitron, graphitron-maven-plugin, and graphitron-mcp.