[raphamorim]

Summary

Makes the C FFI usable for a real native host (built for a SwiftUI macOS frontend): sound, persistent battery saves, and errors instead of aborts.

• Correct mapper for FFI and wasm loads. get_mbc treated a missing file path as "use MBC3 without saves", so every FFI/wasm game ran on MBC3. Each mapper now takes Option<PathBuf> and saves are simply disabled without one.
• On-demand saves. MemoryBankController::save() writes cartridge RAM (MBC3 keeps its RTC prefix). Drop still saves. Writes go to a .gbsave.tmp and are renamed, so a crash never leaves a truncated save. This matters for FFI because the global GAMEBOY static is never dropped.
• No panics on bad input. Gameboy::try_new / Cpu::try_new return Result; new keeps its old behaviour. With panic = "abort" a bad ROM used to kill the host process.
• New FFI functions (added to gameboy.h):
  • load_with_save(bytes, len, rom_path): like load, with .gbsave next to rom_path; returns a status code
  • save(): flush cartridge RAM now
  • enable_audio(): start cpal output, returns the sample rate
  • audio_queued(): queued stereo frames, so hosts can pace frame() to the audio clock (displays run at 60 Hz, the Game Boy at 59.73 Hz)
  • last_error(): message for the last failure
• cpal 0.16 → 0.18. cpal 0.16's CoreAudio supported_configs passes &data_size of an immutable local as an out-parameter. In optimized builds the compiler assumes it stays 0, reserves a zero-sized buffer, and CoreAudio writes to 0x1 (EXC_BAD_ACCESS). Reproduced on macOS 26.5 in release builds; fixed upstream in 0.17.

Toolchain and dependency update

CI's Make desktop build step was failing (on main too): the examples have no lockfile, so they resolve dependencies fresh, and current crates need Rust 1.85+ and edition 2024.

• rust-toolchain: 1.83.0 → 1.99.1
• cpal 0.18, ratatui 0.30, ratatui-image 11, icy_sixel 0.5, base64 0.23, blip_buf 0.2, image 0.25.10, wasm-bindgen / js-sys / web-sys latest
• glutin 0.28 → 0.32. Windowing moved out of glutin, so screen/desktop.rs now runs on winit 0.30 + glutin-winit with an ApplicationHandler. Same window, key mapping, pause-when-unfocused and ~60 FPS pacing; it also updates the GL viewport on resize now.
• ratatui-image is built without its default chafa-dyn feature, which requires the system libchafa via pkg-config.
• blip_buf 0.2 returns Err where 0.1 asserted; those calls now drop the sample instead of aborting.
• Fixes for new clippy lints (repeat_n, is_multiple_of, format width).

Testing

CI passes (lint, tests, desktop build). Locally on macOS 26.5 with Rust 1.99.1:

• make lint (clippy -D warnings), cargo test --release: pass
• cargo build --release --target wasm32-unknown-unknown: builds
• examples/desktop and examples/terminal: build
• Desktop window (new winit/glutin code) runs Pokémon Silver, checked with a screenshot
• cargo build --release --no-default-features --features ffi: builds; tested from a Swift host with Pokémon Silver (MBC3 + RTC + battery): audio callback runs, .gbsave is written (8-byte RTC + 32 KiB RAM)
• Not tested: the terminal frontend interactively, Linux/Windows desktop windows, reloading a save after an in-game save