Model the nested fetcher own outgoing per-field precise edges in CompileDependencyGraphBuilder

R459 registered the <Type>Fetchers node for a fetcher-owning plain-object nesting type and got the schema-shape-to-fetcher wiring edge (FilmMetaType → FilmMetaFetchers) for free. It deliberately did not model the nested fetcher’s own outgoing per-field edges: a nested SplitTableField’s DataLoader methods reference the target type’s projection class; a nested composite / `@nodeId read references NodeIdEncoder. CompileDependencyGraphBuilder.addFieldEdges never sees these fields because they are absent from schema.fields() (and schema.fieldsOf(nestedType) is empty for a coordinate-less nesting type). The TypeSpecReferenceWalk completeness oracle will flag any such edge as a superset gap once a harness fixture exercises it.

This is not a routing one-liner. Folding a nested SplitTableField through addFieldEdges’ `TableTargetField arm would call addConditionsEdge(fetcher, "FilmMeta"), whose hasSqlGeneratingField reads the empty schema.fieldsOf("FilmMeta") and produces the wrong answer, the same fieldsOf blindness over coordinate-less nested types that caused the R459 bug. Conditions attribution (and, more broadly, per-field edge sourcing) over nested types needs its own design that does not depend on the nested type’s SDL coordinates being populated.

Extend IncrementalCompileHarnessTest’s `SCHEMA / SCHEMA_EDITED with a nested field that turns the completeness oracle red once the R459 registration is in place, for example a nested @splitQuery (DataLoader-backed SplitTableField) or a nested composite-@nodeId read on the fetcher-owning nesting type. R459’s own fixture (Film.meta: FilmMeta { language: Language @reference }) uses a single-valued inline TableField precisely so it does not exercise this gap; verified while implementing R459 that disabling the R459 walk left exactly the one FilmMetaType → FilmMetaFetchers gap and nothing else. This item’s fixture should produce a fetcher-outgoing gap (e.g. FilmMetaFetchers → types.<Target> or FilmMetaFetchers → util.NodeIdEncoder) that the oracle catches.

Filed by R459 as its scope-boundary follow-up (see the "Scope boundary" section of nesting-type-fetcher-wiring-graph-edges.md). Related collapse target R459 also names: exposing nested fetcher-owning types and their fields as a derived view on GraphitronSchema so emitter, projection walk, and builder project off one seam; a shared nested-field-with-coordinates view would give this item’s per-field edge sourcing a non-blind fieldsOf to read.