A failed pre-flight check must not leak the PARK= override

_probe wrote the PARK= argument into self.park before running the
pre-flight checks, but the restore sat in the finally inside _guarded --
so a probe refused for a cold extruder or unhomed axes kept the
override. FF_PA_PROBE PARK=0 followed by any refusal would silently
turn parking off for every later FF_PA_CALIBRATE, landing the gram on
the plate instead of down the chute.

The override now goes on inside its own try/finally that covers the
checks too, with the rest of the probe split into _probe_inner.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UBzgZQiUiARJcG1NupWgY2

pkgs/klipper/payload/klipper/klippy/extras/ff_pa.py

@@ -923,9 +923,19 @@ class FFPA:
             raise gcmd.error("%s: PA='%s' is not a number"
                              % (self.name, pa_text))
         y = gcmd.get_float('Y', self.y_start)
+        # PARK= is a per-invocation override of a persistent default, so it
+        # must be undone on EVERY exit -- including a refusal from the checks
+        # below, which run before _guarded gets a finally in place. Leaking it
+        # would flip what the next FF_PA_CALIBRATE does with its gram.
         saved_park = self.park
-        self.park = bool(gcmd.get_int('PARK', int(self.park),
-                                      minval=0, maxval=1))
+        try:
+            self.park = bool(gcmd.get_int('PARK', int(self.park),
+                                          minval=0, maxval=1))
+            self._probe_inner(gcmd, y, pa_text)
+        finally:
+            self.park = saved_park
+
+    def _probe_inner(self, gcmd, y, pa_text):
         tool = self._resolve_tool(gcmd)
         self._check_homed(gcmd)
         self._check_filament(gcmd, tool)
@@ -951,7 +961,6 @@ class FFPA:
                 raise gcmd.error("%s: %s" % (self.name, err))
             finally:
                 self.y_start = saved_y
-                self.park = saved_park
         if self.dry_run:
             return
         extra = ''