diff --git a/android-ffi/src/lib.rs b/android-ffi/src/lib.rs
index 09e0f0e..3cce6e8 100644
--- a/android-ffi/src/lib.rs
+++ b/android-ffi/src/lib.rs
@@ -225,6 +225,21 @@ pub extern "system" fn Java_com_verify_remote_RustBridge_nativeSendMouseMove(
     });
 }
 
+#[no_mangle]
+pub extern "system" fn Java_com_verify_remote_RustBridge_nativeSendMouseRel(
+    _env: JNIEnv,
+    _class: JClass,
+    handle: jlong,
+    dx: jint,
+    dy: jint,
+) {
+    // 协议 v4 的字段是 i16：Kotlin 侧传 Int，越界一律 clamp 而不是静默回绕。
+    // 越界值只可能来自主控端 bug 或恶意对端；clamp 让行为有界且可见（不 panic、不 UB）。
+    let dx = dx.clamp(i16::MIN as i32, i16::MAX as i32) as i16;
+    let dy = dy.clamp(i16::MIN as i32, i16::MAX as i32) as i16;
+    with_session(handle, |s| s.send_mouse_rel(dx, dy));
+}
+
 /// button: 0=左 1=右 其他=中；down: 1=按下 0=抬起
 #[no_mangle]
 pub extern "system" fn Java_com_verify_remote_RustBridge_nativeSendMouseButton(
diff --git a/viewer-core/Cargo.toml b/viewer-core/Cargo.toml
index 9c559cd..32dcb0b 100644
--- a/viewer-core/Cargo.toml
+++ b/viewer-core/Cargo.toml
@@ -20,3 +20,11 @@ rustls.workspace = true
 # headless_check 用软解交叉验证收到的码流合法（库本身刻意不依赖 openh264，
 # 解码在 Android 侧由 MediaCodec 承担）
 openh264 = { version = "0.9.9", features = ["source"] }
+# rel_mouse_proof（3b/V-B1）需要读回 Windows 光标位置来闭环验证相对注入。
+# 仅 examples 使用，不进库本体；库本身仍然平台无关。
+[target.'cfg(windows)'.dev-dependencies]
+windows = { workspace = true, features = [
+    "Win32_Foundation",
+    "Win32_UI_WindowsAndMessaging",
+    "Win32_UI_HiDpi",
+] }
diff --git a/viewer-core/examples/rel_mouse_proof.rs b/viewer-core/examples/rel_mouse_proof.rs
new file mode 100644
index 0000000..6ede895
--- /dev/null
+++ b/viewer-core/examples/rel_mouse_proof.rs
@@ -0,0 +1,185 @@
+//! 3b 桌面验收：相对鼠标（协议 v4）的像素级闭环。
+//!
+//! 为什么必须单独写一个 proof：V-B1 的判据是「位移**恰好**等于请求值」，
+//! 而 Android 侧的真机脚本只能看到 UI 文本，看不到远端指针实际走了多少像素。
+//! 这里直接走完整链路：viewer-core 发 `MouseMoveRel` → QUIC → agent 注入 →
+//! `GetCursorPos` 读回，逐项比对。
+//!
+//! 覆盖判据：
+//! - V-B1a 方向与量值：dx=+50 → +50px，dx=-50 → -50px（误差 ≤1px）
+//! - V-B1b 慢速不丢位移：连发 20 次 dx=+1 → 累计 +20px（误差 ≤2px）
+//! - V-B1c 撞边不积债：右边界 +200 后 -50 → 立即 -50
+//!
+//! 用法（agent 需已启动）：
+//!   cargo run --release -p viewer-core --example rel_mouse_proof -- --host 127.0.0.1 --port 47800 --code t
+//!
+//! 安全：运行前记录光标原位，结束时还原（不污染用户桌面状态）。
+
+use std::time::Duration;
+use viewer_core::{ConnectConfig, Session};
+
+fn arg(name: &str) -> Option<String> {
+    let a: Vec<String> = std::env::args().collect();
+    a.iter()
+        .position(|x| x == name)
+        .and_then(|i| a.get(i + 1))
+        .cloned()
+}
+
+/// 读当前光标（物理像素）。用 windows crate 而不是 shell，避免进程 DPI 差异。
+fn cursor() -> (i32, i32) {
+    use windows::Win32::Foundation::POINT;
+    use windows::Win32::UI::WindowsAndMessaging::GetCursorPos;
+    let mut p = POINT::default();
+    unsafe {
+        let _ = GetCursorPos(&mut p);
+    }
+    (p.x, p.y)
+}
+
+fn set_cursor(x: i32, y: i32) {
+    use windows::Win32::UI::WindowsAndMessaging::SetCursorPos;
+    unsafe {
+        let _ = SetCursorPos(x, y);
+    }
+}
+
+fn screen_size() -> (i32, i32) {
+    use windows::Win32::UI::WindowsAndMessaging::{GetSystemMetrics, SM_CXSCREEN, SM_CYSCREEN};
+    unsafe { (GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN)) }
+}
+
+fn enable_dpi_awareness() {
+    use windows::Win32::UI::HiDpi::{
+        SetProcessDpiAwarenessContext, DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2,
+    };
+    unsafe {
+        let _ = SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+    }
+}
+
+/// 发一串相对增量，每次之间留出注入完成的时间，然后读回光标。
+fn apply_rel(session: &Session, steps: &[(i16, i16)], settle_ms: u64) {
+    for &(dx, dy) in steps {
+        session.send_mouse_rel(dx, dy);
+        // 让 QUIC 上行 + agent 注入 + 光标更新都完成；太小会读到中间态
+        std::thread::sleep(Duration::from_millis(settle_ms));
+    }
+}
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    enable_dpi_awareness();
+    let port: u16 = arg("--port").map(|s| s.parse()).transpose()?.unwrap_or(47800);
+    let code = arg("--code").unwrap_or_else(|| "t".into());
+    let host = arg("--host").unwrap_or_else(|| "127.0.0.1".into());
+
+    let (sw, sh) = screen_size();
+    println!("[proof] screen {sw}x{sh} (physical, DPI-aware)");
+
+    let session = Session::connect(ConnectConfig::direct(&host, port, code)).await?;
+    let (dw, dh) = session.desktop_size();
+    println!("[proof] agent desktop {dw}x{dh}");
+
+    // 记录原位，结束时还原（不污染桌面状态）
+    let (ox, oy) = cursor();
+    println!("[proof] cursor origin ({ox},{oy})");
+
+    let mut failures = 0usize;
+
+    // ---- V-B1a 方向与量值 ----
+    println!("\n=== V-B1a direction & magnitude ===");
+    for &delta in &[50i16, -50i16, 120i16, -120i16] {
+        // 每次都从屏幕中心出发，避免被边界 clamp 干扰量值判定
+        set_cursor(sw / 2, sh / 2);
+        std::thread::sleep(Duration::from_millis(60));
+        let (bx, _) = cursor();
+        apply_rel(&session, &[(delta, 0)], 80);
+        let (ax, _) = cursor();
+        let applied = ax - bx;
+        let ok = (applied - delta as i32).abs() <= 1;
+        println!(
+            "  dx={delta:+5}  from x={bx:4} to x={ax:4}  applied={applied:+5}  {}",
+            if ok { "PASS" } else { "FAIL" }
+        );
+        if !ok {
+            failures += 1;
+        }
+    }
+
+    // 纵向同理（同一套代码路径，但轴不同，clamp 上界不同）
+    for &delta in &[40i16, -40i16] {
+        set_cursor(sw / 2, sh / 2);
+        std::thread::sleep(Duration::from_millis(60));
+        let (_, by) = cursor();
+        apply_rel(&session, &[(0, delta)], 80);
+        let (_, ay) = cursor();
+        let applied = ay - by;
+        let ok = (applied - delta as i32).abs() <= 1;
+        println!(
+            "  dy={delta:+5}  from y={by:4} to y={ay:4}  applied={applied:+5}  {}",
+            if ok { "PASS" } else { "FAIL" }
+        );
+        if !ok {
+            failures += 1;
+        }
+    }
+
+    // ---- V-B1b 慢速小幅不丢位移 ----
+    println!("\n=== V-B1b slow small steps must not be lost ===");
+    {
+        set_cursor(sw / 2, sh / 2);
+        std::thread::sleep(Duration::from_millis(60));
+        let (bx, _) = cursor();
+        // 20 次 dx=+1：若注入层按 mickey 透传，dx=1 会被加速吞成 0 像素（实测如此）
+        let steps: Vec<(i16, i16)> = (0..20).map(|_| (1i16, 0i16)).collect();
+        apply_rel(&session, &steps, 45);
+        std::thread::sleep(Duration::from_millis(120));
+        let (ax, _) = cursor();
+        let applied = ax - bx;
+        let ok = (applied - 20).abs() <= 2;
+        println!("  20 x dx=+1  from x={bx} to x={ax}  applied={applied:+}  (expect +20)  {}",
+            if ok { "PASS" } else { "FAIL" });
+        if !ok {
+            failures += 1;
+        }
+    }
+
+    // ---- V-B1c 撞边不积债 ----
+    println!("\n=== V-B1c edge clamp leaves no step debt ===");
+    {
+        set_cursor(sw - 1, sh / 2);
+        std::thread::sleep(Duration::from_millis(60));
+        let (bx, _) = cursor();
+        apply_rel(&session, &[(200, 0)], 80);
+        let (mx, _) = cursor();
+        let clamped = mx - bx;
+        // 回滑必须立即生效（若累积器"记住"了被 clamp 丢掉的 200px，这里会先空转）
+        apply_rel(&session, &[(-50, 0)], 80);
+        let (ax, _) = cursor();
+        let back = ax - mx;
+        let ok = clamped == 0 && (back + 50).abs() <= 1;
+        println!(
+            "  at right edge x={bx}: +200 -> applied {clamped:+} (clamped); -50 -> applied {back:+}  {}",
+            if ok { "PASS" } else { "FAIL" }
+        );
+        if !ok {
+            failures += 1;
+        }
+    }
+
+    // 还原光标
+    set_cursor(ox, oy);
+
+    println!("\n========== RESULT ==========");
+    if failures == 0 {
+        println!("REL MOUSE PROOF PASS (all V-B1a/b/c checks)");
+    } else {
+        println!("REL MOUSE PROOF FAIL ({failures} checks failed)");
+    }
+    session.close().await;
+    if failures > 0 {
+        std::process::exit(1);
+    }
+    Ok(())
+}
diff --git a/viewer-core/src/lib.rs b/viewer-core/src/lib.rs
index 56f7a91..349d88f 100644
--- a/viewer-core/src/lib.rs
+++ b/viewer-core/src/lib.rs
@@ -618,6 +618,21 @@ impl Session {
         self.send_input(InputEvent::Text { units });
     }
 
+    /// 协议 v4：发送**相对**鼠标位移（单位：被控端桌面物理像素）。
+    ///
+    /// 与 [`Session::send_text`] 同样的空值纪律：零位移不占一条消息——它没有注入语义，
+    /// 只会白占一个 QUIC 帧（触摸事件里 `dx==0 && dy==0` 是常态，手指静止时每帧都发）。
+    ///
+    /// 语义是「从远端指针当前位置移动 (dx,dy)」，远端负责 clamp 到桌面内。
+    /// 主控端**不要**先算绝对坐标再发——那就退化成绝对模式，失去相对鼠标的意义
+    /// （本机真鼠标同时移动时会跳变）。
+    pub fn send_mouse_rel(&self, dx: i16, dy: i16) {
+        if dx == 0 && dy == 0 {
+            return;
+        }
+        self.send_input(InputEvent::MouseMoveRel { dx, dy });
+    }
+
     /// 请求被控端强制关键帧（解码器错误/跳帧后的恢复路径）。
     pub fn request_keyframe(&self) {
         let _ = self.tx.send(Command::KeyFrameReq);