Reject PA calibrations with no result or bad sensor data

bdpressure.py leaves the extruder at the last PA_CALIBRATE test value
(0.098) when it finds no result, and _PA_AFTER_CALIBRATE saved that as
the calibrated PA (lane1 after an AFC pause, lane5 after the sensor went
silent). A run is now rejected, with nothing cached or written to
Spoolman, when the PA is still at the end of the scan, the printer
paused during the test, or bd_pressure gave too few or too few different
readings. The previous valid PA (or fallback_pa) is applied instead.

bdpressure_check reports pa_points and pa_distinct from the bdpressure
module's last PA_CALIBRATE data for this.

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

macros/pressure_advance/bd_pa_spoolman.cfg

@@ -196,6 +196,19 @@ variable_travel_speed: 300
 variable_acc_to_decel_factor: 50
 # Minimum PA delta before we bother re-saving the cached value
 variable_write_threshold: 0.002
+# A calibration is rejected (nothing cached or written to Spoolman, the
+# previous PA is kept) when:
+#  - its result is the last PA_CALIBRATE test value: bdpressure.py found no
+#    result and left the extruder at the end of its scan (0..49 x 0.002),
+#  - the printer paused during the test (e.g. an AFC filament fault),
+#  - bd_pressure gave fewer than min_points readings or fewer than
+#    min_distinct different ones (sensor silent or hung; needs
+#    bdpressure_check.py, otherwise this check is skipped).
+variable_sweep_end_pa: 0.098
+variable_min_points: 10
+variable_min_distinct: 8
+# PA applied when a rejected lane has no earlier cached value
+variable_fallback_pa: 0.04
 # Spoolman URL and the custom "extra" field name used to push calibrated
 # PA values back to the spool record (so the value travels with the
 # spool, not just with this printer's local save_variables cache).
@@ -469,6 +482,34 @@ gcode:
     # triggered -- which happens after PA_CALIBRATE (queued earlier by
     # the caller) has fully completed. So this read is fresh and correct.
     {% set new_pa = printer.extruder.pressure_advance|default(0.0)|float %}
+
+    # Reject runs where the sensor or the printer had a problem
+    {% set problems = [] %}
+    {% if new_pa >= cfg.sweep_end_pa|float - 0.0001 %}
+        {% set _ = problems.append("no result (PA left at the end of the test range, %.3f)" % new_pa) %}
+    {% endif %}
+    {% if printer.pause_resume.is_paused %}
+        {% set _ = problems.append("the printer paused during the test") %}
+    {% endif %}
+    {% if 'bdpressure_check' in printer %}
+        {% set bdp = printer.bdpressure_check %}
+        {% set points = bdp.pa_points|default(-1)|int %}
+        {% set distinct = bdp.pa_distinct|default(-1)|int %}
+        {% if points >= 0 and points < cfg.min_points|int %}
+            {% set _ = problems.append("only %d readings from bd_pressure (sensor not answering?)" % points) %}
+        {% elif distinct >= 0 and distinct < cfg.min_distinct|int %}
+            {% set _ = problems.append("only %d different readings out of %d (sensor stuck?)" % (distinct, points)) %}
+        {% endif %}
+    {% endif %}
+
+    {% if problems %}
+        # A cached value at the end of the scan is an earlier failed run, not a PA
+        {% set use_cache = cache_found and cached_pa < cfg.sweep_end_pa|float - 0.0001 %}
+        {% set keep = cached_pa if use_cache else cfg.fallback_pa|float %}
+        RESPOND TYPE=error MSG="PA calibration for {lane} (spool {spool_id}) rejected: {problems|join('; ')}. Nothing saved; using PA={'%.4f' % keep} ({'cached' if use_cache else 'fallback'}). Fix the cause, then LANE_CALIBRATE_PA LANE={lane} FORCE=1"
+        SET_PRESSURE_ADVANCE ADVANCE={keep}
+        M117 PA cal rejected: {lane}
+    {% else %}
     {action_respond_info("Calibration complete for %s: PA=%.4f" % (lane, new_pa))}
     M117 PA cal done: {new_pa|round(4)}
 
@@ -480,6 +521,7 @@ gcode:
     {% else %}
         {action_respond_info("PA change below threshold (%.4f), skipping cache/Spoolman write" % cfg.write_threshold|float)}
     {% endif %}
+    {% endif %}