Fix K8850 mouse binding format (native 17-byte mouse_data)

The 8850 uses a different mouse packet format than K884x. Confirmed via
Frida capture of mini_keyboard.exe and PR kriomant#154 by yawor:

- Position [5] starts mouse_data (not 0x00 padding like keyboard type)
- Format: [1, 4, 0, 0, modifier, 0, 0, buttons, 0, 0, dx, 0, 0, dy, 0, 0, wheel]
- Mouse modifier uses same firmware IDs (F1=Ctrl, F2=Shift, F3=Alt)
- Button bitmap: 1=left, 2=right, 4=middle

Hardware tested: clicks, scroll wheel, and mouse move all confirmed working.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: skarard

src/keyboard/k8850.rs

@@ -4,7 +4,7 @@ use anyhow::{ensure, Result};
 use clap::Parser;
 use nom::{IResult, branch::alt, bytes::complete::tag, character::complete::alpha1, combinator::{map, map_res, value}, sequence::preceded};
 
-use super::{Key, Keyboard, Macro, KeyboardEvent, Modifier, MouseEvent, MouseAction, send_message};
+use super::{Key, Keyboard, Macro, KeyboardEvent, Modifier, MouseEvent, MouseAction, MouseModifier, send_message};
 
 
 /// LED modes for the K8850 firmware (confirmed via hardware testing).
@@ -213,34 +213,37 @@ impl Keyboard for Keyboard8850 {
                 msg.push(0x00); // [8]
                 msg.push(low);  // [9] consumer code
             }
-            Macro::Mouse(MouseEvent(MouseAction::Move(dx, dy), modifier)) => {
-                msg.push(0x00); // [6] binding_mode
-                msg.push(0x00); // [7]
-                msg.push(0x00); // [8]
-                msg.push(0x00); // [9]
-                msg.extend_from_slice(&[0x05, modifier.map_or(0, |m| m as u8), 0, *dx as u8, *dy as u8]);
-            }
-            Macro::Mouse(MouseEvent(MouseAction::Drag(buttons, dx, dy), modifier)) => {
-                msg.push(0x00); // [6]
-                msg.push(0x00); // [7]
-                msg.push(0x00); // [8]
-                msg.push(0x00); // [9]
-                msg.extend_from_slice(&[0x05, modifier.map_or(0, |m| m as u8), buttons.as_u8(), *dx as u8, *dy as u8]);
-            }
-            Macro::Mouse(MouseEvent(MouseAction::Click(buttons), modifier)) => {
-                ensure!(!buttons.is_empty(), "buttons must be given for click macro");
-                msg.push(0x00); // [6]
-                msg.push(0x00); // [7]
-                msg.push(0x00); // [8]
-                msg.push(0x00); // [9]
-                msg.extend_from_slice(&[0x01, modifier.map_or(0, |m| m as u8), buttons.as_u8()]);
-            }
-            Macro::Mouse(MouseEvent(MouseAction::Wheel(delta), modifier)) => {
-                msg.push(0x00); // [6]
-                msg.push(0x00); // [7]
-                msg.push(0x00); // [8]
-                msg.push(0x00); // [9]
-                msg.extend_from_slice(&[0x03, modifier.map_or(0, |m| m as u8), 0, 0, 0, *delta as u8]);
+            Macro::Mouse(MouseEvent(action, modifier)) => {
+                // 8850 mouse format (confirmed via Frida capture + PR #154 by yawor):
+                // Position [5] in the full packet is the start of mouse_data (not 0x00 like keyboard).
+                // Format: [1, 4, 0, 0, modifier, 0, 0, buttons, 0, 0, dx, 0, 0, dy, 0, 0, wheel]
+                msg.pop(); // Remove the header's 0x00 at [5]; mouse_data provides its own bytes
+                let mut mouse_data = [0u8; 17];
+                mouse_data[0] = 1;
+                mouse_data[1] = 4;
+                mouse_data[4] = modifier.map_or(0, |m| mouse_modifier_firmware_id(m));
+
+                match action {
+                    MouseAction::Move(dx, dy) => {
+                        mouse_data[10] = *dx as u8;
+                        mouse_data[13] = *dy as u8;
+                    }
+                    MouseAction::Drag(buttons, dx, dy) => {
+                        eprintln!("warning: drag may not work correctly on 8850 firmware (button hold + move sent as separate actions)");
+                        mouse_data[7] = buttons.as_u8();
+                        mouse_data[10] = *dx as u8;
+                        mouse_data[13] = *dy as u8;
+                    }
+                    MouseAction::Click(buttons) => {
+                        ensure!(!buttons.is_empty(), "buttons must be given for click macro");
+                        mouse_data[7] = buttons.as_u8();
+                    }
+                    MouseAction::Wheel(delta) => {
+                        mouse_data[16] = *delta as u8;
+                    }
+                }
+
+                msg.extend_from_slice(&mouse_data);
             }
         };
 
@@ -311,6 +314,15 @@ fn modifier_firmware_id(m: Modifier) -> u8 {
     }
 }
 
+/// Map a MouseModifier to the 8850 firmware's modifier ID.
+fn mouse_modifier_firmware_id(m: MouseModifier) -> u8 {
+    match m {
+        MouseModifier::Ctrl => 0xF1,
+        MouseModifier::Shift => 0xF2,
+        MouseModifier::Alt => 0xF3,
+    }
+}
+
 impl Keyboard8850 {
     pub fn new(buttons: u8, knobs: u8) -> Result<Self> {
         ensure!(buttons <= 16 && knobs <= 3, "8850 supports up to 16 buttons and 3 knobs");