Serialize RemainderOptionBytes without a length prefix in the Rust client

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Problem

RemainderOptionBytes (the hooked type behind the data argument of write, initialize and set_data in the Rust client) serializes Some(bytes) with Vec::<u8>::serialize, which writes a 4-byte length prefix. The IDL types this argument as a remainderOptionTypeNode of bytesTypeNode: the bytes are the rest of the instruction data, with no prefix. The JS client encodes it with getOptionEncoder(getBytesEncoder(), { prefix: null }), and the program reads everything after the fixed fields as the data.

So a Rust client that builds a write with data: Some(vec![1, 2, 3]).into() and offset: 7 sends the args [7, 0, 0, 0, 3, 0, 0, 0, 1, 2, 3] instead of [7, 0, 0, 0, 1, 2, 3], and the program writes [3, 0, 0, 0, 1, 2, 3] into the buffer. The same happens for initialize and set_data. Decoding has the opposite problem: deserialize_reader expects a length prefix and maps any error to None, so valid instruction data [1, 2, 3] decodes as None.

Fix

In clients/rust/src/hooked/remainder_options.rs, RemainderOptionBytes now writes the raw bytes for Some, and reads the rest of the input when deserializing: no bytes left is None, otherwise Some(bytes). This matches the JS option decoder with prefix: null. RemainderOptionSeed is unchanged, since Seed is a fixed [u8; 16] and has no prefix. The generated code is not touched.

This is a different problem from the ones listed in #86.

Test

I added unit tests to the same file: Some(vec![1, 2, 3]) serializes to [1, 2, 3], None to [], remaining bytes decode to Some and empty input to None, values round-trip, and WriteInstructionArgs { offset: 7, data: Some([1, 2, 3]) } serializes to [7, 0, 0, 0, 1, 2, 3]. Three of these fail without the fix. With the fix, cargo test on clients/rust passes, and cargo fmt --check and cargo clippy --all-targets --all-features -- -D warnings (nightly-2026-01-22) are clean.

This change was prepared with AI assistance (Claude) and reviewed by me before submitting.

🤖 Generated with Claude Code