fix(q5_max): fix RAW_EPSIZE and via_command_kb hook conflict

Two build errors:

1. RAW_EPSIZE undeclared — usb_descriptor.h is not in scope when
   keymap.c is compiled through Keychron's build path. Replace all
   uses with HID_PACKET_SIZE (= 32), now defined in hid_protocol.h.

2. via_command_kb duplicate symbol — keychron_raw_hid.c already defines
   via_command_kb (non-weak) so we cannot redefine it in keymap.c.

Fix by adding a weak kc_raw_hid_rx_kb() extension hook to
keychron_raw_hid.c (following the same pattern as kc_rgb_matrix_rx).
kc_raw_hid_rx() now calls this hook from its default case instead of
returning false directly. The keymap overrides kc_raw_hid_rx_kb() to
handle our custom HID command range (0x40-0x7E).

keyboards/keychron/common/keychron_raw_hid.c

@@ -85,6 +85,11 @@ void get_firmware_version(uint8_t *data) {
 
 __attribute__((weak)) void kc_rgb_matrix_rx(uint8_t *data, uint8_t length) {}
 
+/* Default no-op implementation; override in keymap.c to handle custom IDs. */
+__attribute__((weak)) bool kc_raw_hid_rx_kb(uint8_t *data, uint8_t length) {
+    return false;
+}
+
 bool kc_raw_hid_rx(uint8_t *data, uint8_t length) {
     switch (data[0]) {
         case KC_GET_PROTOCOL_VERSION:
@@ -185,7 +190,7 @@ bool kc_raw_hid_rx(uint8_t *data, uint8_t length) {
 
 #endif
         default:
-            return false;
+            return kc_raw_hid_rx_kb(data, length);
     }
 
     raw_hid_send(data, length);

keyboards/keychron/common/keychron_raw_hid.h

@@ -63,3 +63,17 @@ enum {
     REPORT_RATE_GET,
     REPORT_RATE_SET,
 };
+
+/**
+ * Keyboard-level Raw HID extension hook.
+ *
+ * Called by kc_raw_hid_rx() for any command ID not handled by Keychron's own
+ * protocol (0xA0-0xAB range).  The default weak implementation returns false
+ * so that unrecognised commands fall through to VIA.
+ *
+ * Override this in your keymap to handle custom command IDs without
+ * conflicting with Keychron's via_command_kb() definition.
+ * Return true if the packet was fully handled (including calling
+ * raw_hid_send() if a reply is needed), false to let VIA process it.
+ */
+bool kc_raw_hid_rx_kb(uint8_t *data, uint8_t length);

keyboards/keychron/q5_max/ansi_encoder/keymaps/via/hid_protocol.h

@@ -80,6 +80,14 @@
 // ---------------------------------------------------------------------------
 #define HID_APP_NAME_MAX 28u
 
+// ---------------------------------------------------------------------------
+// Packet size
+// ---------------------------------------------------------------------------
+// Matches RAW_EPSIZE (QMK raw HID endpoint size = 32 bytes).  Defined here
+// so keymap code does not depend on usb_descriptor.h being in scope, which
+// it is not when compiled through Keychron's build path.
+#define HID_PACKET_SIZE 32u
+
 // ---------------------------------------------------------------------------
 // Convenience: first byte of payload as an absolute packet index
 // ---------------------------------------------------------------------------

keyboards/keychron/q5_max/ansi_encoder/keymaps/via/keymap.c

@@ -18,6 +18,7 @@
 #include "keychron_common.h"
 #include "chord_unicode.h"
 #include "raw_hid.h"
+#include "keychron_raw_hid.h"
 #include "hid_protocol.h"
 
 // Tap Dance declarations
@@ -77,18 +78,20 @@ static uint8_t g_hid_brightness = 0;
 
 // Send the current layer state to the host / bridge application.
 static void hid_send_layer_sync(uint8_t layer, uint8_t locked_mask) {
-    uint8_t data[RAW_EPSIZE] = {0};
+    uint8_t data[HID_PACKET_SIZE] = {0};
     data[HID_OFF_CMD]                           = HID_CMD_LAYER_SYNC;
     data[HID_OFF_SRC]                           = HID_DEV_Q5MAX;
     data[HID_OFF_FLAGS]                         = 0;
     data[HID_PAYLOAD(HID_LAYER_OFF_ACTIVE)]     = layer;
     data[HID_PAYLOAD(HID_LAYER_OFF_LOCKED)]     = locked_mask;
-    raw_hid_send(data, RAW_EPSIZE);
+    raw_hid_send(data, HID_PACKET_SIZE);
 }
 
 // Handle a Raw HID packet for our custom command range (0x40-0x7E).
-// Called from via_command_kb(); must call raw_hid_send() for any reply.
+// Overrides the weak kc_raw_hid_rx_kb() hook in keychron_raw_hid.c, which is
-bool via_command_kb(uint8_t *data, uint8_t length) {
+// called by kc_raw_hid_rx() for any command ID not handled by Keychron's own
+// protocol.  Must call raw_hid_send() directly for any reply.
+bool kc_raw_hid_rx_kb(uint8_t *data, uint8_t length) {
     uint8_t cmd = data[HID_OFF_CMD];
 
     // Only intercept our custom command range; let VIA handle everything else.
@@ -102,13 +105,13 @@ bool via_command_kb(uint8_t *data, uint8_t length) {
         case HID_CMD_LAYER_SYNC: {
             if (flags & HID_FLAG_QUERY) {
                 // Host requests current state — reply without changing anything.
-                uint8_t resp[RAW_EPSIZE] = {0};
+                uint8_t resp[HID_PACKET_SIZE] = {0};
                 resp[HID_OFF_CMD]                       = HID_CMD_LAYER_SYNC;
                 resp[HID_OFF_SRC]                       = HID_DEV_Q5MAX;
                 resp[HID_OFF_FLAGS]                     = HID_FLAG_RESPONSE;
                 resp[HID_PAYLOAD(HID_LAYER_OFF_ACTIVE)] = get_highest_layer(layer_state);
                 resp[HID_PAYLOAD(HID_LAYER_OFF_LOCKED)] = (uint8_t)locked_layers;
-                raw_hid_send(resp, RAW_EPSIZE);
+                raw_hid_send(resp, HID_PACKET_SIZE);
             } else {
                 // Host or peer keyboard is pushing a new active layer.
                 uint8_t new_layer  = data[HID_PAYLOAD(HID_LAYER_OFF_ACTIVE)];