🔧 Sanity-check SWITCHING_TOOLHEAD_X_POS (#23985)

Marlin/src/inc/SanityCheck.h

@@ -1301,6 +1301,14 @@ static_assert(Y_MAX_LENGTH >= Y_BED_SIZE, "Movement bounds (Y_MIN_POS, Y_MAX_POS
   #endif
 #endif
 
+/**
+ * Generic Switching Toolhead requirements
+ */
+#if ANY(SWITCHING_TOOLHEAD, MAGNETIC_SWITCHING_TOOLHEAD, ELECTROMAGNETIC_SWITCHING_TOOLHEAD)
+  constexpr float thpx[] = SWITCHING_TOOLHEAD_X_POS;
+  static_assert(COUNT(thpx) == EXTRUDERS, "SWITCHING_TOOLHEAD_X_POS must be an array EXTRUDERS long.");
+#endif
+
 /**
  * Switching Toolhead requirements
  */

buildroot/tests/BIGTREE_GTR_V1_0

@@ -31,7 +31,8 @@ exec_test $1 $2 "BigTreeTech GTR | 6 Extruders | Quad Z + Endstops" "$3"
 restore_configs
 opt_set MOTHERBOARD BOARD_BTT_GTR_V1_0 SERIAL_PORT -1 \
         EXTRUDERS 3 TEMP_SENSOR_1 1 TEMP_SENSOR_2 1 \
-        SERVO_DELAY '{ 300, 300, 300 }'
+        SERVO_DELAY '{ 300, 300, 300 }' \
+        SWITCHING_TOOLHEAD_X_POS '{ 215, 0 ,0 }'
 opt_enable SWITCHING_TOOLHEAD TOOL_SENSOR
 exec_test $1 $2 "BigTreeTech GTR | Switching Toolhead | Tool Sensors" "$3"