Add documentation about unknown command 4

FEATURE_CAPABILITIES.md

@@ -87,3 +87,21 @@ Connected:                true
 - CLI flags for unsupported features are hidden in the help menu
 - CLI exits with error code 1 when attempting to use unsupported features
 - Tray UI shows read-only markers based on device capabilities
+
+## Protocol Notes
+
+### Undocumented Commands
+
+**Command 4 (Cloud II Wireless)**: An undocumented HID command that occasionally appears as an asynchronous notification from the headset. This command is **not handled** by the official HyperX NGenuity2 software, which simply logs it to debug traces.
+
+- **Appearance**: Sporadic, trigger conditions unknown
+- **Official behavior**: Ignored by NGenuity2
+- **HyperHeadset behavior**: Logged for debugging purposes
+- **Investigation findings**:
+  - Does NOT trigger on charging cable connect/disconnect
+  - Does NOT trigger on battery level changes
+  - Not related to any user-controllable feature
+  - May be firmware artifact from Cloud Flight S (which uses cmd 4 for button presses)
+  - Cloud II Wireless and Cloud II Wireless DTS both ignore this command
+
+This is documented for transparency but can be safely ignored during normal operation.

Headset_protocol.md

@@ -53,6 +53,7 @@ Byte    Value   Description
 | 1      | 0x01 | Get Connection Status  | Query wireless connection status      |
 | 2      | 0x02 | Get Battery Level      | Query current battery percentage      |
 | 3      | 0x03 | Get Charging Status    | Query charging state                  |
+| 4      | 0x04 | Unknown/Unused         | Undocumented notification (ignored)   |
 | 8      | 0x08 | Mute Status (Response) | Microphone mute status (in responses) |
 | 9      | 0x09 | Initialization         | Sent during device initialization     |
 | 17     | 0x11 | Get Firmware Version   | Query firmware version (4 bytes)      |
@@ -97,6 +98,27 @@ Response: [0B 00 BB 03 <status> ...]
   - `0x02` = Fully charged
   - `0x03` = Charge error
 
+#### Command 4 - Undocumented/Unused Notification
+
+```
+Response: [0B 00 BB 04 <data> ...]
+```
+
+- **Purpose:** Unknown - Not handled by official HyperX NGenuity2 software
+- **Note:** This command appears sporadically as an asynchronous notification from the headset
+- **Not user-initiated:** This is an unsolicited notification from the device, not sent by the host
+- **Official behavior:** The official NGenuity2 software logs but does not process this command
+- **Implementation:** HyperHeadset logs the data when received for debugging purposes
+- **Trigger conditions:** Unknown - does NOT trigger on charging cable connect/disconnect or battery level changes
+- **Data format:** Unknown - bytes [4-8] are logged for analysis
+- **Recommendation:** Safe to ignore - likely a spurious firmware notification or leftover from other headset models
+
+**Investigation notes:**
+
+- Command 4 exists in Cloud Flight S firmware for button press handling, but Cloud II Wireless has no such buttons
+- Neither Cloud II Wireless nor Cloud II Wireless DTS firmware handles this command
+- May be a firmware artifact or unused notification channel
+
 #### Set Auto Power Off (Cmd 24)
 
 ```

src/devices/cloud_ii_wireless.rs

@@ -228,6 +228,15 @@ impl Device for CloudIIWireless {
                             Duration::from_secs(minutes as u64 * 60),
                         )])
                     }
+                    4 => {
+                        // Command 4: Charge limit or battery management
+                        // This may be sent asynchronously when charging state changes
+                        println!(
+                            "Charge limit/battery management response (cmd 4): data={:?}",
+                            &response[4..8]
+                        );
+                        None
+                    }
                     9 | 29 => {
                         // Commands 9 and 29 are seen during initialization but purpose unclear
                         println!("Initialization response (cmd {})", response[3]);