diff --git a/context/multiplayer.md b/context/multiplayer.md
index 5de9eef..690e681 100644
--- a/context/multiplayer.md
+++ b/context/multiplayer.md
@@ -130,9 +130,12 @@ the drive being on). Fix: `BT_GOTO` now enables forced mode itself + supplies it
 holds and shoots instead of ramming). (2) The steering used the `gDriveHeading` SCALAR MIRROR (seeded to 0),
 but MP pilots spawn facing a non-zero heading, so the beeline steered the WRONG way. Fix: compute the heading
 error from the mech's ACTUAL forward (`localToWorld`'s -Z axis), signed angle to the target. (3) The goto turn
-was routed through `controlsMapper->turnDemand`, which zeroes out in -net (the mapper key-bridge only shapes
-the local viewpoint mech there) — the heading froze and A drove straight past B. Fix: apply the goto turn to
-the orientation integration DIRECTLY (`if(gBTGotoActive) turn=gBTGotoTurn`), after the mapper read.
+was routed through `controlsMapper->turnDemand`, which read 0 in -net — the heading froze and A drove straight
+past B. Fix: apply the goto turn to the orientation integration DIRECTLY (`if(gBTGotoActive) turn=gBTGotoTurn`),
+after the mapper read. **CAUSE FOUND LATER (task #51): turnDemand zeroed because `controlMode` was pointer
+garbage — the `pilotArray[1]` shrunk-span overrun (see [[reconstruction-gotchas]] §5), MP-only because solo's
+overrun wrote 0==BasicMode. Fixed at the root (10-slot array); the direct goto-turn stays (harmless, and it
+skips the 1-frame mapper latency). KEYBOARD turning in MP was restored by the root fix.**
 VERIFIED 2-node: A `BT_GOTO="enemy"` alone (no autodrive) drives `dist 1673→231 m`, holds at range, `mechPicks=59`,
 autofire → **B hdlr=192, DESTROYED** — a fully automated human-style cross-pod kill via the real beam path
 (not the FORCE_DMG hook). Solo un-regressed (plain autodrive + goto both work). `scratchpad/mp_kill_test.sh`;
diff --git a/context/reconstruction-gotchas.md b/context/reconstruction-gotchas.md
index d0b10a8..b744d92 100644
--- a/context/reconstruction-gotchas.md
+++ b/context/reconstruction-gotchas.md
@@ -90,6 +90,15 @@ The 33-agent RESOURCE_AUDIT fixed 8 such bugs (docs/RESOURCE_AUDIT.md). [T2]
   member (HeatSink `heatState@0x184` == `heatAlarm.GetLevel()`). → route to the accessor.
 - **Phantom field:** a member at an offset PAST the object (Generator `shortFlag@0x25C` is
   really `*(owner+0x190)+0x25c` the msg-manager). → remove; read the real source.
+- **Shrunk-span array:** a binary FIXED-SPAN block declared as `member[1]` ("variable length"
+  comment) — every write past slot 0 stomps the members declared after it.  Archetype:
+  `MechControlsMapper::pilotArray` — the binary reserves 0x15C..0x183 (10 slots); the `[1]`
+  declaration let MP's `FillPilotArray` write the PEER's `Player*` over `controlMode`
+  ("can't turn in MP": turn shaping dispatched on pointer garbage → `turnDemand=0`), MASKED
+  in solo because the overrun wrote 0 == BasicMode.  → size the array to the binary's
+  inter-member span ((next-member offset − array offset) / stride) + clamp the fill loops.
+  Caught live with cdb `ba w4` on the compiled member address (log `&member` from the ctor,
+  offset delta gives the compiled position).  [T2]
 `GaugeAlarm54` = 0x54 (the real `AlarmIndicator`; STATUS level at +0x14, so
 `subsystem+0x184 == heatAlarm+0x14 == GetLevel()`); `SubsystemConnection` = 0xC. [T1]
 
diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index 04675f4..04c0ed0 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -1688,7 +1688,9 @@ void
 					<< " stickX=" << controlsMapper->stickPosition.x
 					<< " -> speedDemand=" << controlsMapper->speedDemand
 					<< " turnDemand=" << controlsMapper->turnDemand
-					<< " mode=" << controlsMapper->controlMode << "\n" << std::flush;
+					<< " mode=" << controlsMapper->controlMode
+					<< " mapper=" << (void*)controlsMapper
+					<< " &mode=" << (void*)&controlsMapper->controlMode << "\n" << std::flush;
 			}
 		}
 
diff --git a/game/reconstructed/mechmppr.cpp b/game/reconstructed/mechmppr.cpp
index 411b67f..887ca7b 100644
--- a/game/reconstructed/mechmppr.cpp
+++ b/game/reconstructed/mechmppr.cpp
@@ -342,6 +342,10 @@ MechControlsMapper::MechControlsMapper(
 	controlMode		= BasicMode;
 	displayMode		= 0;
 	pilotArrayPage		= 0;
+	if (getenv("BT_MODE_LOG"))
+		DEBUG_STREAM << "[mode-ctor] mapper=" << (void*)this
+			<< " controlMode=" << (int)controlMode
+			<< " &controlMode=" << (void*)&controlMode << "\n" << std::flush;
 
 	//
 	// Recenter the torso articulation: current yaw/pitch <- neutral yaw/pitch.
@@ -364,7 +368,8 @@ MechControlsMapper::MechControlsMapper(
 
 	pilotArrayBuilt	= False;
 	pilotIDs			= 0;
-	pilotArray[0]		= 0;
+	for (int pi = 0; pi < PilotArraySlots; ++pi)
+		pilotArray[pi] = 0;
 
 	Check_Fpu();
 }
@@ -913,6 +918,13 @@ void
 		}
 	}
 
+	// Capacity clamp: the binary reserves 10 slots (local + up to 9 remotes;
+	// an 8-pod game fits).  pilotCount beyond that would overrun the block in
+	// the binary too -- clamp so the `<= pilotCount` zero-loop (which zeroes
+	// the local slot 0 PLUS pilotCount remotes, faithful) stays in bounds.
+	if (pilotCount > PilotArraySlots - 1)
+		pilotCount = PilotArraySlots - 1;
+
 	pilotIDs = new int[pilotCount];								// FUN_004022b0
 
 	for (int i = 0; i <= pilotCount; ++i)
diff --git a/game/reconstructed/mechmppr.hpp b/game/reconstructed/mechmppr.hpp
index 3673f88..d2b9079 100644
--- a/game/reconstructed/mechmppr.hpp
+++ b/game/reconstructed/mechmppr.hpp
@@ -176,8 +176,17 @@ class Pilot;
 		ControlsButton		torsoCenter;		// @0x154
 
 		int					pilotArrayPage;		// @0x158  (which "page" of pilots)
-		Pilot				*pilotArray[1];		// @0x15C  [0]=local; [1..] remote
-											// (variable length; pilotCount entries)
+		// FIXED 10-SLOT block, the binary's own reservation: 0x15C..0x183 =
+		// (pilotArrayBuilt@0x184 - 0x15C)/4 = 10 pointers ([0]=local, [1..9]
+		// remote; an 8-pod game + the local fits).  The old `[1]` "variable
+		// length" declaration made EVERY write past slot 0 stomp the members
+		// declared after it: in MP, FillPilotArray wrote the PEER's Player
+		// pointer over controlMode (the turn shaping dispatched on pointer
+		// garbage -> turnDemand 0 -> "I can't turn"); in solo the zero-loop
+		// wrote 0 there, masked only because 0 == BasicMode.  Caught live via
+		// cdb `ba w4` on &controlMode (task #51).
+		enum { PilotArraySlots = 10 };
+		Pilot				*pilotArray[PilotArraySlots];	// @0x15C..0x183
 
 		enum ControlMode {
 			BasicMode	 = 0,