fix: wait out a remote's long press across the millis() wrap

The 500 ms wait that tells a short press from a long one compared
now > await, so a press just before the wrap acted at once. It now
compares the wrap-safe difference. Reconcile Q21 in
SHADE_BEHAVIOUR_PLAN.md.

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

docs/SHADE_BEHAVIOUR_PLAN.md

@@ -92,7 +92,7 @@ The decisions are the user's. Each question comes with a recommended answer, and
   - ~~A group's SunFlag or Flag doesn't make other groups work their flags out again.~~ Fixed (Q20).
   - The self-echo (Q5) and merging group commands into the frame rule (Q8).
   - `lastFrame` doing two jobs (the Q6 revisit).
-  - The 500 ms long-press deadline is compared as `now > await`, which isn't wrap-safe (not tested).
+  - ~~The 500 ms long-press deadline isn't wrap-safe.~~ Fixed (Q21).
 
 ## Constraints
 

src/ShadeBehaviour.cpp

@@ -360,7 +360,8 @@ void ShadeBehaviour::onWaitingFrame(uint32_t now) {
     return;
   }
   if(this->lastFrame.processed) return;
-  if(this->lastFrame.await > 0 && (now > this->lastFrame.await)) {
+  // Wrap-safe: await is now + 500 when the press began.
+  if(this->lastFrame.await > 0 && static_cast<int32_t>(now - this->lastFrame.await) > 0) {
     somfy_commands cmd = this->transformCommand(this->lastFrame.cmd);
     switch(cmd) {
       case somfy_commands::StepUp:

test/test_shadebehaviour/test_shadebehaviour.cpp

@@ -324,6 +324,17 @@ static void test_remote_my_when_idle_goes_to_the_favorite_after_half_a_second()
   r.wait(200);
   ASSERT_POS(60, r.st().target);
 }
+static void test_remote_my_waits_half_a_second_across_the_millis_wrap() {
+  Rig r;
+  r.b.restore(0, 0, 60, -1);
+  r.now = 0xFFFFFFFF - 200;
+  r.press(somfy_commands::My);
+  // The deadline is past the wrap; it still waits for it.
+  r.wait(300);
+  ASSERT_POS(0, r.st().target);
+  r.wait(300);
+  ASSERT_POS(60, r.st().target);
+}
 static void test_remote_my_held_sets_the_favorite() {
   Rig r;
   r.b.restore(30, 0, 60, -1);
@@ -629,6 +640,7 @@ int main(int argc, char **argv) {
   RUN_TEST(test_flipped_shade_sends_the_other_way);
   RUN_TEST(test_remote_down_and_my_stop);
   RUN_TEST(test_remote_my_when_idle_goes_to_the_favorite_after_half_a_second);
+  RUN_TEST(test_remote_my_waits_half_a_second_across_the_millis_wrap);
   RUN_TEST(test_remote_my_held_sets_the_favorite);
   RUN_TEST(test_remote_held_up_on_a_tilt_motor_tilts);
   RUN_TEST(test_remote_step_uses_the_frames_step_size);