Constant WILDCOPY_OVERLENGTH 

pub const WILDCOPY_OVERLENGTH: usize = crate::decoding::buffer_backend::WILDCOPY_OVERLENGTH; // 32usize

SIMD wildcopy overshoot slack carried by every decoder backend (currently 32 bytes). Sized so the AVX2 chunked kernel in simd_copy::copy_bytes_overshooting (32-byte stride on x86-64) can fire on tail copies near the end of a fixed-capacity output buffer. Donor zstd’s WILDCOPY_OVERLENGTH is also 32 bytes today; this matches that contract.

Public so callers sizing an output slice for crate::decoding::FrameDecoder::decode_all can size frame_content_size + WILDCOPY_OVERLENGTH symbolically without duplicating the value. Use the const reference rather than a hardcoded literal — simd_copy::copy_bytes_overshooting already ships an AVX-512 64-byte chunked kernel, and the slack may grow further to reliably enable that wider kernel at buffer tails (mirroring how the bump from 16 → 32 enabled the AVX2 32-byte kernel at the tail).