Audio: footsteps arrive on the FIRST stride -- the 10-20 s warm-up bug

User report: footfalls silent for the first 10-20 s of every mission (all
mechs), then solid.  Root cause was three interlocking layers, each measured
with timestamped traces:

1. The authored footstep volume chain (LocalAcceleration [0,10]->ctl100 +
   LocalVelocity [0,0.6]->ctl101 through authored N=30/N=15
   AudioControlSmoothers, fill 0) hangs off the SOURCE's watcher chain
   (scale watches smoother watches mixer watches source), and an idle
   source's chain executes only at Start attempts -- one smoother sample
   per stride.
2. Each hop is frame-gated (AudioComponent::ExecuteWatchers,
   DefaultAudioFrameDelay), so any burst collapses to one execution.
3. The transient drop gate (vol < 0.3, AUDREND) rejected every Start while
   the smoother average crawled up 1/30th per attempt -> ~25 dropped strides
   before the first audible step, then per-frame execution while playing
   kept it warm forever ("solid after that").

Fixes (engine-level, each documented in place):
- AudioScaleOf<T>::Execute now sends EVERY poll (scales are continuous
  value-feeders; the base bitwise change-gate -- Motion::operator== is
  memcmp -- froze on our deterministic gait math, where the original's
  noisy physics floats never bit-repeated.  Triggers/matchers keep the
  change gate: their semantics are edge-based).
- Component/AudioComponent::PrimeWatchers(passes): recursive, GATE-FREE
  watcher pump; AUDREND runs 30 passes on every transient Start request so
  the authored smoothers evaluate at their true steady state before the
  drop gate reads the volume.
- localAcceleration derives via the binary's exact structure: 15-sample
  ring buffers of the raw position derivative + dt (ctor part_012.c:9836,
  derive :15169-15195), in the PerformAndWatch tail so it runs every frame.
- AttributeWatcherOf::GrabCurrentValue private -> protected (the scale
  override calls it).

Verified (30 s walk from cold start): drops 25 -> 3 (the survivors are
authentic quiet-stride gating: first gentle strides at vol ~0.28 vs the 0.3
gate), footfalls deliver from the first stride, 43 delivered with live
per-stride gain variation.  Diag traces added: [accwatch]/[fsscale]/
[smooth]/[smoothcfg]/[motionscalecfg] + timestamps on DROP/volset.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

engine/MUNGA/AUDCMP.cpp

@@ -856,6 +856,11 @@ AudioControlSmoother::AudioControlSmoother(
 	MemoryStream_Read(stream, &initial_fill_value);
 	audioControlAverage.SetSize(number_of_samples, initial_fill_value);
 
+	if (getenv("BT_ATTRBIND_LOG")) { static int s_sm=0; if (s_sm++<40)
+		DEBUG_STREAM << "[smoothcfg] this=" << (void*)this << " ctlID=" << (int)control_ID
+			<< " samples=" << (int)number_of_samples << " fill=" << initial_fill_value
+			<< "\n" << std::flush; }
+
 	AudioControlSmootherX(
       audio_component,
       entity,
@@ -955,6 +960,14 @@ void
 	{
       audioControlAverage.Add(control_value);
 
+      if (getenv("BT_AUDIO_SPATIAL")) { static int s_sa=0;
+         if ((controlID == 100 || controlID == 101) && s_sa++ < 3000)
+            DEBUG_STREAM << "[smooth] t=" << (GetTickCount() % 1000000)
+               << " this=" << (void*)this << " ctl=" << (int)controlID
+               << " in=" << control_value
+               << " avg=" << audioControlAverage.CalculateOlympicAverage()
+               << "\n" << std::flush; }
+
       Check(audioComponentSocket.GetCurrent());
       audioComponentSocket.GetCurrent()->ReceiveControl(
          controlID,