go: interface-typed variable assigned a concrete type across closures — CALLS target is the interface member (decision + fixture) #2038

Summary

When an interface-typed variable is declared in one place, assigned a local concrete type inside one closure, and called inside another closure, the call currently has no proper source attribution and (under receiver-qualified QNs, #1913) no target at all. Before writing a fixture the target representation has to be decided; this issue records that decision.

Corpus shape (kubernetes, test/e2e/apimachinery/crd_validation_ratcheting.go)

• :48 — var restmapper meta.RESTMapper
• :74 — restmapper = &fakeRESTMapper{...} inside a ginkgo.BeforeEach closure
• :93 — restmapper.KindFor(gvr) inside a different closure (applyPatch)
• :913 — func (f *fakeRESTMapper) KindFor(...)

Today the edge is crd_validation_ratcheting.go.__file__ -> ...apimachinery.KindFor — source is the File node, not a function, and the target is a same_module flat-QN hash (pkg.KindFor, 0.9, cand=1), i.e. a name coincidence, not a resolution. Under receiver-qualified QNs there is no row.

Decision: the CALLS target is the interface member

meta.RESTMapper.KindFor — the static dispatch target. Rationale: go_lsp.c already routes registered interface receivers deliberately to the interface-resolution branch ("Registered interface receivers must reach the interface-resolution branch below"), and the census classification ratified interface members as the correct static target for the same idiom (informers.Core -> factory.go:355). Resolving to the sole concrete implementer instead (fakeRESTMapper.KindFor) would be higher-precision on test doubles but diverges from the interface-first rule everywhere else in the graph.

What the fix needs

1. Source attribution: the call inside the closure must be attributed to the enclosing function (or the closure node), not to __file__.
2. The declared type of restmapper must survive across closures. go_invalidate_control_flow_aliases (go_lsp.c:1396) exists precisely to discard reassigned bindings — a declared interface type should not be invalidated by a concrete assignment, because the interface is the static type regardless of what is assigned.
3. Fixture: three closures in one file mirroring the shape above; assert applyPatch -> meta.RESTMapper.KindFor and the absence of a __file__ source.