Purge check: accept load-check firmware v2; chamber load levels first

- bdpressure_check.py accepted only extension version 1. The sensor now
  runs firmware version 2 (bytes 54-65 unchanged, diagnostics added), so
  every purge check reported bd_pressure as not answering. Accept 1 and 2.
- _LOAD_FOR_CHAMBER: the Blobifier only purges with the QGL applied, so
  the load before the chamber soak skipped its purge (0.0 mm extruded).
  Level the gantry and home Z first when the QGL is not applied.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

extras/bdpressure_check.py

@@ -2,7 +2,7 @@
 #
 # Uses the I2C connection the existing [bdpressure <name>] section already
 # set up. Before writing anything it reads the extension marker (bytes
-# 54-55 = 0xBD 0x01). On stock firmware the marker is missing and every
+# 54-55 = 0xBD + version 1 or 2). On stock firmware the marker is missing and every
 # command only reports "not available": nothing is written, because
 # writing past the stock register table would land in the sensor's RAM.
 #
@@ -27,8 +27,12 @@
 
 REG_EXT = 54          # first byte of the extension
 REG_CTRL = 56
-EXT_LEN = 12          # bytes 54-65
-EXT_MAGIC = (0xBD, 0x01)
+EXT_LEN = 12          # bytes 54-65, the same in version 1 and 2
+EXT_MAGIC = 0xBD
+# Version 2 (load-check firmware 20261015 and later) only adds diagnostics
+# at 66-71. Accepting only version 1 made the purge check report the sensor
+# as not answering after the firmware update.
+EXT_VERSIONS = (1, 2)
 
 
 class BDPressureCheck:
@@ -62,7 +66,8 @@ class BDPressureCheck:
             self.status['available'] = False
             return False
         data = bytearray(self.i2c.i2c_read([REG_EXT], EXT_LEN)['response'])
-        if len(data) < EXT_LEN or tuple(data[0:2]) != EXT_MAGIC:
+        if (len(data) < EXT_LEN or data[0] != EXT_MAGIC
+                or data[1] not in EXT_VERSIONS):
             self.status['available'] = False
             return False
         u16 = lambda i: data[i] | (data[i + 1] << 8)

macros/print/print_start_end.cfg

@@ -108,6 +108,16 @@ gcode:
         {% else %}
           RESPOND MSG="Chamber heating: loading and purging {ns.lane} ({new.material}, {tool}) before the chamber heats"
         {% endif %}
+        # The Blobifier only purges with the QGL applied: without it AFC
+        # loaded the lane and skipped the purge. Level now (PRINT_START
+        # levels again on the soaked bed) and home Z after it.
+        {% if printer.quad_gantry_level and not printer.quad_gantry_level.applied %}
+          _GUARD_ON PHASE=warmup_qgl
+          QUAD_GANTRY_LEVEL
+          _GUARD_ON PHASE=warmup_z_home
+          G28 Z
+          _GUARD_OFF
+        {% endif %}
         M109 S{temps|max}
         {tool}
         _LOAD_FOR_CHAMBER_VERIFY LANE={ns.lane}