Batch 2 of the test-arch reframe. These three are codegen-SHAPE tests,
not data-row tests: each subject is a distinct node shape (N_IDENT
module-global read; chained N_INDEX m[i][k]; index-base node-kind). A
[N]struct row-table would interpose its own N_INDEX/N_DOT lowering and
mask the shape under test, so each uses per-shape @test fns with direct
asserts (rob-ratified rule: table where the row is data, per-fn where
the row is a codegen shape). Lossless from the matching
989_{gunsigned,chainidx,idxarg}_run.c; additive (C kept); both stages green.
