帧同步丢一包不该停住：三帧冗余、空洞检测与补帧

// server/crates/battle/src/room.rs
match msg {
    c2s::Msg::InputCmd(input) if self.state == RoomState::Running => {
        if !self.arbiter.is_kicked(seat) {
            self.pending[index] = input.input;
        }
    }
    c2s::Msg::FrameRequest(request) => {
        self.send_frame_range(seat, request.from, request.to)
    }
    _ => {}
}

fn on_tick(&mut self) {
    let frame = encode_frame(&self.pending);
    self.frames.push(frame);
    self.broadcast_frames_tail();
}

// plans/active/tank-moba/common/protocol.md
message InputCmd {
  uint32 frame_index = 1; // 只做客户端延迟统计
  fixed32 input = 2;      // buttons | angle | strength | aim
}

message FrameRequest {
  uint32 from = 1;        // 闭区间
  uint32 to = 2;
}

message Frames {
  uint32 first_frame = 1;
  repeated bytes frames = 2;
}

// server/crates/battle/src/room_send.rs
pub(super) fn broadcast_frames_tail(&mut self) {
    let count = self.cfg.redundant_frames.max(1) as usize;
    let len = self.frames.len();
    let start = len.saturating_sub(count);
    let frames = self.frames[start..]
        .iter()
        .map(|frame| frame.to_vec())
        .collect();

    self.broadcast_frames(Frames {
        first_frame: start as u32,
        frames,
    });
}

// client/Assets/HotUpdate/Game.Net/Battle/FrameBuffer.cs
public bool AddFrame(FrameInputs frame)
{
    if (_lastConsumed >= 0 && frame.FrameIndex <= (uint)_lastConsumed)
        return false;

    if (_frames.ContainsKey(frame.FrameIndex))
        return false;

    _frames.Add(frame.FrameIndex, frame);
    ReportGap();
    return true;
}

public bool TryConsumeNext(out FrameInputs frame)
{
    uint next = NextFrame();
    if (!_frames.TryGetValue(next, out frame))
        return false;

    _frames.Remove(next);
    _lastConsumed = next;
    _hasLastGap = false;
    ReportGap();
    return true;
}

// FrameBuffer.ReportGap 的核心分支
uint expected = NextFrame();
if (_frames.ContainsKey(expected)) return;

foreach (uint frameIndex in _frames.Keys)
{
    if (frameIndex <= expected) continue;

    uint from = expected;
    uint to = frameIndex - 1;
    if (!_hasLastGap || _lastGapFrom != from || _lastGapTo != to)
    {
        _hasLastGap = true;
        _lastGapFrom = from;
        _lastGapTo = to;
        _onGap(from, to);
    }
    return;
}

encoded_sparse_bytes=10
encoded_empty_bytes=2
after_first_packet expected=0 buffered=2 gaps=0-1
consumed=0,1,2,3
gap_events=0-1,1-1
duplicate_old_frame_accepted=False
three_frame_tail_ready=3

cd "$PROJECT_ROOT"
dotnet test shared/GameNet.Tests/GameNet.Tests.csproj \
  --filter 'FullyQualifiedName~FrameBufferTests' --no-restore --nologo

# 自定义 Runner 实际执行全套
Total tests: 49. Passed: 49. Failed: 0.
real 0.86s

cargo test --manifest-path server/Cargo.toml \
  -p battle room_tick_tests --locked -- --nocapture

test result: ok. 2 passed; 0 failed; 49 filtered out
real 0.90s