fix(ui): debounce the Hall sensor poll against reed-switch contact bounce

pollHallSensor() acted on the raw pin reading immediately, unlike every other
physical-input path in this file (MomentaryButton, pollCardKB()'s own
last-raw edge check). A cheap mechanical reed switch -- one of the two
sensor types the docs explicitly recommend wiring here, alongside a
solid-state Hall IC -- can chatter for a few ms while the magnet crosses the
trigger distance, so a poll every loop() tick during that window could flip
_locked and fire _display->turnOff()/turnOn() repeatedly in that short span:
wasted work on any panel, and a real cost on e-ink where each is a slow
full-panel operation.

A raw reading now has to hold steady for HALL_DEBOUNCE_MS (25ms, same
threshold as MomentaryButton's ISR_DEBOUNCE_MS) before it replaces
_hall_magnet_present and triggers the lock/unlock actions.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.cpp

@@ -2255,11 +2255,24 @@ void UITask::pollCardKB() {
 // there's nothing to show), opening unlocks and wakes it, with no combo or
 // keypress either way. Independent of Auto-lock (Settings > Display), which is
 // a timeout-driven setting -- this is a direct physical event.
+//
+// Debounced against a mechanical reed switch chattering for a few ms as the
+// magnet crosses the trigger distance -- a raw flip only becomes the new
+// _hall_magnet_present once it's been steady for HALL_DEBOUNCE_MS, so a bounce
+// can't fire the lock/unlock actions (each including a full display
+// off/on -- slow and disruptive on e-ink) more than once per real transition.
 void UITask::pollHallSensor() {
 #if defined(PIN_HALL_SENSOR)
-  bool present = HALL_ACTIVE_HIGH ? (digitalRead(PIN_HALL_SENSOR) == HIGH)
+  bool raw = HALL_ACTIVE_HIGH ? (digitalRead(PIN_HALL_SENSOR) == HIGH)
-                                   : (digitalRead(PIN_HALL_SENSOR) == LOW);
+                               : (digitalRead(PIN_HALL_SENSOR) == LOW);
-  if (present == _hall_magnet_present) return;
+  if (raw != _hall_candidate) {
+    _hall_candidate = raw;
+    _hall_candidate_since = millis();
+  }
+  if (_hall_candidate == _hall_magnet_present) return;   // no debounced change yet
+  if (millis() - _hall_candidate_since < HALL_DEBOUNCE_MS) return;   // not steady long enough
+
+  bool present = _hall_candidate;
   _hall_magnet_present = present;
 
   if (present) {   // cover closed

examples/companion_radio/ui-new/UITask.h

@@ -219,6 +219,13 @@ class UITask : public AbstractUITask {
   #define HALL_ACTIVE_HIGH 0
 #endif
   bool _hall_magnet_present = false;
+  // Contact-bounce guard for a mechanical reed switch (a Hall-effect IC reads
+  // clean, but the docs recommend either): a raw reading only replaces
+  // _hall_magnet_present once it's held steady for HALL_DEBOUNCE_MS, same
+  // threshold and reasoning as MomentaryButton's ISR_DEBOUNCE_MS.
+  static const uint32_t HALL_DEBOUNCE_MS = 25;
+  bool     _hall_candidate = false;
+  uint32_t _hall_candidate_since = 0;
 #endif
   void pollHallSensor();