v2.1-rc1 is the first release candidate of the v2.1 line. Built on the fceux codebase, this release continues the Rust migration: CPU and PPU are now in Rust as the canonical engine. Behavioral changes since v2.0_hotfix2 are driven by NESdev wiki spec parity rather than fceux heritage: $2007 read buffer, $2007 increment parity, NMI dispatch, VBL/NMI dot-alignment, rendering-off v-walk gate. Test infra: nestest + savestate MD5 golden regenerated; KagamiQA at grade B. 0x2F TEST_SPHIT_DIRECT deferred to v2.1.1.6+. Real-machine verification on MMC3 / sprite0 / VBL-NMI edges is requested.
v2.1-rc1 是 v2.1 系列首个发布候选。本版本在 fceux 基础上继续推进 Rust 化：CPU 与 PPU 均已重写为 Rust 作为 canonical engine，C++ PPU 仅作临时 fallback 保留。自 v2.0_hotfix2 以来行为变更以 NESdev wiki 真机规范为准：$2007 write 不再改 vram_buffer、$2007 increment 奇偶对齐、NMI dispatch delay 修正、VBL/NMI dot 对齐到 dot=0、rendering-off v-walk 门控。测试基建同步：重新生成 nestest + savestate MD5 golden，KagamiQA 达 grade B（8 个 blargg 桶 advisory，无 blocking，无回归）。0x2F TEST_SPHIT_DIRECT 推迟到 v2.1.1.6+。请在 MMC3 / sprite0 / VBL-NMI 边界实机验证。