fix: complete HM42 monochrome image planes

src/ppclock/protocol.py

@@ -29,6 +29,17 @@ def select_rxtx_uuid(firmware_revision: str | None) -> str:
         return RXTX_CHAR_UUID_LEGACY
     return RXTX_CHAR_UUID
 
+
+def requires_complete_image_planes(firmware_revision: str | None) -> bool:
+    """Whether a nominally mono full-screen upload still needs both planes.
+
+    The HM42 Web-BLE implementation always sends the 400x300 black/white plane
+    followed by a red plane before opcode 01.  Omitting the second plane leaves
+    HM42 rendering stale/uninitialised red data (observed as a red noisy screen).
+    """
+    revision = (firmware_revision or "").strip().upper()
+    return revision.startswith("HM42_AIO")
+
 MODES = {
     **{f"image{i}": bytes([0xE1, 0x00, 0x00 + i]) for i in range(4)},
     "calendar1": bytes.fromhex("e10103"),