Fix throttle-detent Abs() macro bug + KB analog-throttle + slide diagnostics (task #50)

Uncommitted work from the speed-model + peer-motion investigation:
 - btl4mppr.cpp: the L4MechControlsMapper full-throttle detent used the
   unparenthesized Abs() macro (STYLE.H:118) on an expression -- Abs(throttlePos
   - 1.0f) mis-expands to -(throttlePos + 1.0f), always <= 0.05, so the detent
   snapped throttle to full EVERY frame.  Diff into a temp first (same class as
   the 7615ecd angular-resync Abs fix).
 - context/pod-hardware.md: document the decomp-verified analog-continuous pod
   throttle path (RIO Ranger 0-800 counts, 0.05 deadband, no notching; '5 speeds'
   is false) from workflow w0odszxro.
 - mech4.cpp: BT_SLIDE/[mslide] per-frame slide diagnostics (peer position moving
   while legs in stand; master decel profile) -- used to prove the stop-slide is a
   peer leg-SM-winds-down-early desync, not master momentum.  Env-gated.

The 'pretty good' coupled-motion gameplay state is already shipped (a9ab3db).

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

game/reconstructed/btl4mppr.cpp

@@ -349,7 +349,12 @@ L4MechControlsMapper::MessageHandlerSet&
 		//
 		// (1) Full-throttle detent.
 		//
-		if (Abs(throttlePosition - 1.0f) <= 0.05f)		// _DAT_004d1ac0 / _DAT_004d1ac4
+		// NB: the Abs() macro (STYLE.H:118) is unparenthesized -- Abs(throttlePosition
+		// - 1.0f) mis-expands to -(throttlePosition + 1.0f) on the false branch (always,
+		// since throttle <= 1), which is <= 0.05 UNCONDITIONALLY -> the detent used to
+		// snap throttle to full every frame.  Diff into a temp so the macro sees one token.
+		const Scalar _thrOff = throttlePosition - 1.0f;
+		if (((_thrOff < 0.0f) ? -_thrOff : _thrOff) <= 0.05f)		// _DAT_004d1ac0 / _DAT_004d1ac4
 		{
 			throttlePosition = 1.0f;					// @0x11c
 		}

game/reconstructed/mech4.cpp

@@ -2189,6 +2189,30 @@ void
 					localToWorld = localOrigin;				// refresh with the coupled position
 				}
 
+				// SLIDE probe (BT_SLIDE): per-frame, log when the peer position MOVES
+				// while its legs are in STAND (legState 0) -- the user's "sliding after
+				// legs stopped".  Reports move magnitude, offset to authority, leg state.
+				if (getenv("BT_SLIDE"))
+				{
+					static Point3D s_slPrev; static int s_slInit = 0;
+					const int ls = (int)legStateAlarm.GetLevel();
+					if (s_slInit)
+					{
+						const float dx = (float)(localOrigin.linearPosition.x - s_slPrev.x);
+						const float dz = (float)(localOrigin.linearPosition.z - s_slPrev.z);
+						const float mv = sqrtf(dx * dx + dz * dz);
+						if (ls == 0 && mv > 0.02f)		// standing but moving = slide
+						{
+							Vector3D off; off.Subtract(updateOrigin.linearPosition, localOrigin.linearPosition);
+							DEBUG_STREAM << "[slide] move=" << mv
+								<< " legAdv=" << replLegAdv
+								<< " offToAuth=" << (float)off.Length()
+								<< " legState=" << ls << "\n" << std::flush;
+						}
+					}
+					s_slPrev = localOrigin.linearPosition; s_slInit = 1;
+				}
+
 				// PEER-DRIFT probe (BT_MIRDIV, 1s max): how far the peer's coupled
 				// position wanders from the last-received authority (updateOrigin)
 				// before a record re-anchors it -- the other end of the snap.
@@ -3422,6 +3446,21 @@ void
 				// impact freezes travel as before.)
 				const Scalar travelAdv = s_realControls ? legAdv : adv;
 				const Scalar localAdv = travelAdv * dir;
+				// MASTER-SLIDE probe (BT_SLIDE): does the MASTER itself advance while its
+				// legs are in STAND (legState 0)?  If yes -> authentic momentum coast, the
+				// peer correctly mirrors it.  If the master travelAdv reaches 0 exactly
+				// when legState reaches 0 -> the master stops clean and the peer's stand-
+				// slide is a peer leg-SM-too-fast desync.  Logs the decel profile.
+				if (getenv("BT_SLIDE"))
+				{
+					const int mls = (int)legStateAlarm.GetLevel();
+					const float ta = (float)(travelAdv < 0 ? -travelAdv : travelAdv);
+					if (ta > 0.005f)		// master still moving
+						DEBUG_STREAM << "[mslide] travelAdv=" << travelAdv
+							<< " legState=" << mls
+							<< " legCycle=" << legCycleSpeed
+							<< " thr=" << throttle << "\n" << std::flush;
+				}
 				linearSpeed = (localAdv < 0.0f ? -localAdv : localAdv) * invDt;	// forward ground speed -> LinearSpeed gauge
 				Vector3D localVel(0.0f, 0.0f, -localAdv * invDt);	// exact frame distance as velocity
 				Matrix34 orient;									// rotation from the heading (set @ line ~626)