91/91 regression tests pass (+ffi-04-fp-struct).
Single-file regression net for the all-float / all-double aggregate
ABI path:
FQuad — 16 B, 4×f32 (same slot as ffi-02's Vec4f)
DQuad — 32 B, 4×f64 (UIEdgeInsets-shape — the f32-vs-f64 landmine)
Already nominally covered by ffi-02's Vec4f, but pinning it as a
focused single-file test means a future ABI rule change that breaks
the HFA path fails *this* test directly without a noisy drag-in from
the multi-shape baseline.
DQuad at 32 B straddles the AAPCS64 HFA limit (≤4 floats of same
type, total ≤64 B); it stays as a struct value passed through
v0..v3 rather than going indirect. The snapshot confirms the values
arrive intact.
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