Fan out the str-cap read (933-936) and store (937-939) families into in-language @test files, following the 932 str_elem_cap template. Additive: the *_run.c stay in the C corpus (they are the only wwstage-runtime net for these cs==ww byte-id-blind shapes); de-dup deferred to fold 6.
Per-shape @test fns, not a data table: each fn varies the codegen shape (base reg / chain depth / tuple return-ABI / store position), so the row-array idiom (blocked by #111) would lose coverage. Read family keeps the spoil()/register-clobber + junk==44 discrimination where the .c has it; store family pre-poisons the slot via a path distinct from the store under test. Asserts are primitives only.
