Expand description
Deterministic ChaCha20-backed standard-normal f64 stream.
This is the canonical Gaussian source for Rust-side rotation matrix
generation. It uses ChaCha20 (via rand_chacha::ChaCha20Rng) for the
uniform stream and the polar Box-Muller transform to emit independent
N(0, 1) samples in f64.
The exact recipe is specified in
docs/design/rust/numerical-semantics.md §R1 and matches the pseudo-
code in docs/plans/rust/phase-13-rotation-numerics.md. Any change
here invalidates every rotation fixture under
tests/fixtures/rotation/.