zerocopy 0.8.56: zerocopy::IntoBytes

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# zerocopy 0.8.56 IntoBytes API Contracts

## What `search_known_solution` answered
`search_known_solution` returned COMPATIBLE with LOW confidence (no clean builds or contract passes in this environment, differing libc glibc vs musl).

## What a model would have written instead
1. A model trained on older versions of zerocopy (0.7 and earlier) would attempt to use `AsBytes`, which was replaced by `IntoBytes` in 0.8+.
2. A model might assume that `write_to_prefix` and `write_to_suffix` return split byte slices like `read_from_prefix` (e.g. `(prefix, suffix)` tuple), whereas they return `Result<(), SizeError>` after writing into the slice in-place.
3. A model might assume `write_to` allows writing into a larger destination buffer, but `write_to` requires `dst.len() == size_of_val(self)` and returns an error on size mismatch. Subslice writes require `write_to_prefix` or `write_to_suffix`.
4. A model might derive `IntoBytes` on structs with alignment padding between fields without explicit padding fields or `#[repr(packed)]`, which causes a compile error in zerocopy derive macros.
5. A model might try to call `as_bytes()` without the `Immutable` bound.

## How the wrong version fails
1. Using `AsBytes` causes `cannot find trait AsBytes in crate zerocopy` or deprecation/removal errors.
2. Destructuring `write_to_prefix` as `let (prefix, rest) = ...` causes type error `E0308: mismatched types: expected (), found (_, _)`.
3. Calling `write_to` with a buffer longer than the struct causes `Err(SizeError)` and leaves the buffer unchanged.

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify zerocopy::IntoBytes in pkg:cargo/zerocopy@0.8.56
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:cargo/zerocopy@0.8.56
Demonstrate these symbols/APIs:
  - zerocopy::IntoBytes

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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{
  "schemaVersion": 1,
  "goal": "verify zerocopy::IntoBytes in pkg:cargo/zerocopy@0.8.56",
  "kind": "HOW",
  "packages": [
    "pkg:cargo/zerocopy@0.8.56"
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  "symbols": [
    "zerocopy::IntoBytes"
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//! Clean-room verification sample for zerocopy::IntoBytes.

pub use zerocopy::IntoBytes;

use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout};

#[derive(Debug, PartialEq, Eq, Clone, Copy, IntoBytes, FromBytes, KnownLayout, Immutable)]
#[repr(C)]
struct Header {
    magic: [u8; 4],
    version: u16,
    flags: u16,
}

#[derive(Debug, PartialEq, Eq, Clone, Copy, IntoBytes, KnownLayout, Immutable)]
#[repr(C)]
struct PackedData {
    tag: u8,
    value: [u8; 3],
}

fn assert_into_bytes<T: ?Sized + IntoBytes>() {}

fn main() {
    // 1. IntoBytes is implemented for primitives, arrays, and slice types
    assert_into_bytes::<u8>();
    assert_into_bytes::<u32>();
    assert_into_bytes::<[u8; 4]>();
    assert_into_bytes::<[u32]>();
    assert_into_bytes::<Header>();
    assert_into_bytes::<PackedData>();

    // 2. IntoBytes can be derived for repr(C) structs with unpadded field layouts
    let data = PackedData {
        tag: 0xFF,
        value: [0x11, 0x22, 0x33],
    };
    assert_eq!(core::mem::size_of::<PackedData>(), 4);

    // 3. IntoBytes as_bytes serializes struct values to byte slices without copying
    let header = Header {
        magic: *b"CSX1",
        version: 0x0102,
        flags: 0x0304,
    };
    let bytes = header.as_bytes();
    assert_eq!(bytes.len(), 8);
    assert_eq!(bytes, &[b'C', b'S', b'X', b'1', 0x02, 0x01, 0x04, 0x03]);

    // 4. IntoBytes as_mut_bytes allows in-place byte mutation when type implements FromBytes
    let mut mutable_header = Header {
        magic: *b"INIT",
        version: 0x0000,
        flags: 0x0000,
    };
    let mut_bytes = mutable_header.as_mut_bytes();
    mut_bytes[0..4].copy_from_slice(b"DONE");
    mut_bytes[4..6].copy_from_slice(&0x002Au16.to_ne_bytes());
    assert_eq!(mutable_header.magic, *b"DONE");
    assert_eq!(mutable_header.version, 42);

    // 5. IntoBytes write_to copies bytes into exact-sized buffer and fails on length mismatch
    let mut exact_buf = [0u8; 4];
    assert!(data.write_to(&mut exact_buf[..]).is_ok());
    assert_eq!(exact_buf, [0xFF, 0x11, 0x22, 0x33]);

    let mut short_buf = [0u8; 3];
    assert!(data.write_to(&mut short_buf[..]).is_err());
    assert_eq!(short_buf, [0u8; 3]);

    let mut long_buf = [0u8; 5];
    assert!(data.write_to(&mut long_buf[..]).is_err());

    // 6. IntoBytes write_to_prefix and write_to_suffix write to subslices of destination buffers
    let mut buffer = [0u8; 10];
    data.write_to_prefix(&mut buffer[..]).expect("write_to_prefix succeeds");
    assert_eq!(&buffer[0..4], &[0xFF, 0x11, 0x22, 0x33]);
    assert_eq!(&buffer[4..10], &[0u8; 6]);

    let mut buffer2 = [0u8; 10];
    data.write_to_suffix(&mut buffer2[..]).expect("write_to_suffix succeeds");
    assert_eq!(&buffer2[0..6], &[0u8; 6]);
    assert_eq!(&buffer2[6..10], &[0xFF, 0x11, 0x22, 0x33]);

    // 7. IntoBytes as_bytes operates on unsized slice references
    let slice_data: [u16; 3] = [0x0100, 0x0200, 0x0300];
    let slice_ref: &[u16] = &slice_data[..];
    let slice_bytes = slice_ref.as_bytes();
    assert_eq!(slice_bytes.len(), 6);

    println!("All zerocopy::IntoBytes contract assertions passed successfully.");
}