diff --git a/context/locomotion.md b/context/locomotion.md
index 39522f6..0d303ad 100644
--- a/context/locomotion.md
+++ b/context/locomotion.md
@@ -311,6 +311,23 @@ resolved with gait v5, no shadow code changed — though (a) may have contribute
 T4]; (c) genuine slope burial when the quad is flat/mis-tilted (the depth-bias margin is finite).
 Check `[shadowobj]` tag lines and `[sync]`/`BT_SYNC_LOG` before touching bias/tilt.
 
+## CROUCH -- COMPLETE 2026-08-06 [T1 decode / T2 full-cycle + MP benched]
+The manual's CROUCH button (streamed 0x13; glass key F4), end to end: DuckRequest (mech id 0x1a
+@0049fa00) latches duckState@0x398 -> the master posture block (mech4, from the dark master-perf
+@0x4a9cf0-0x4aa0af): posture selector @0x3f8 (mode 9/10/2/3/4 block, NOVICE simLive lockout,
+myomer-alive gate) -> standing: SetLegAnimation(2) ('sqd', squat down; LegClipFinished case-2
+PARKS the pose + leg alarm 1) / ducked: SetLegAnimation(3) ('squ', rise; case-3 alarm 0);
+stability alarm flips; ForceUpdate(8)+(1) ships the type-3 state record -- peers pose the squat
+for FREE (screenshot receipt: the crouched crimson madcat from the observer's cockpit,
+duckmpA_031). Clip data verified from BTL4.RES (root joint drops -2.22, knees +-1.14; squ/sqd
+are exact mirrors; interior 'squi/sqdi' variants ship for all 8 chassis). Full solo cycle
+benched (BT_BTNTEST + BT_BTNTEST2): squat -> hold (joints steady for minutes) -> rise ->
+standing zeros. Myomer speed-cripple feeder (@004b8be3) still deferred [T3] -- see mech4 banner.
+RESIDUAL (open-questions): the pilot's own cockpit EYE height does not ride the root drop
+(the interior clip authors joint-0 translation for exactly that; the DPLEyeRenderable chain
+composition needs a look).  Bench traps for reruns: MP button delivery can miss if pressed
+during round-start jitter (press >= poll 900 after GO); diags all BT_DUCK_LOG-gated.
+
 ## Key Relationships
 - Detail: `docs/P3_LOCOMOTION.md`. Uses: [[asset-formats]] (SKL/ANI), [[decomp-reference]] (offsets).
 - Feeds: [[combat-damage]] (collision→damage), [[rendering]] (shadow/visual-conform).
diff --git a/context/open-questions.md b/context/open-questions.md
index 6a452fe..20b7b5d 100644
--- a/context/open-questions.md
+++ b/context/open-questions.md
@@ -1142,3 +1142,10 @@ Gitea #116 and `experience-levels.md`.
 - **des_night-family pages have subtle fog deltas** (both sets near-black); arena/polar night
   pages carry the dramatic 5↔40 near-plane swing. If testers report "searchlight does nothing"
   on some maps, it's page authoring, not the mechanism.
+
+## Crouch residual (2026-08-06 — the feature itself is LIVE, [[locomotion]] §CROUCH)
+- **Pilot eye height does not ride the root drop.** The interior squat clip animates joint 0
+  (ball+translation, −2.22) precisely so the cockpit eye lowers; the joint holds (probe-verified)
+  and the eye's segment chain passes through jointlocal, yet the cockpit view returns to standing
+  height after the squat parks. Suspect: DPLEyeRenderable's parent-chain composition not
+  including the BallTranslateJointRenderable's live matrix. Cosmetic (body + replication correct).
diff --git a/engine/MUNGA_L4/L4CTRL.cpp b/engine/MUNGA_L4/L4CTRL.cpp
index b5ea06d..28924c9 100644
--- a/engine/MUNGA_L4/L4CTRL.cpp
+++ b/engine/MUNGA_L4/L4CTRL.cpp
@@ -2624,6 +2624,13 @@ void
 		Verify(rio_event.Data.Unit < ButtonCount);
 		temp = rio_event.Data.Unit + 1;
 
+		// DIAG (BT_DUCK_LOG): the mode mask a press dispatches under -- the
+		// crouch-button (0x13) MP-delivery hunt (mode-gated streamed rows).
+		if (getenv("BT_DUCK_LOG"))
+			DEBUG_STREAM << "[duck] RIO press unit=0x" << std::hex
+				<< (int)rio_event.Data.Unit << " modeMask=0x"
+				<< (unsigned)mode_mask << std::dec << "\n" << std::flush;
+
 		Check(&buttonGroup[rio_event.Data.Unit]);
 		buttonGroup[rio_event.Data.Unit].Update(&temp, mode_mask);
 		//----------------------------------------
diff --git a/engine/MUNGA_L4/L4PADRIO.cpp b/engine/MUNGA_L4/L4PADRIO.cpp
index 26ff495..3acf1a2 100644
--- a/engine/MUNGA_L4/L4PADRIO.cpp
+++ b/engine/MUNGA_L4/L4PADRIO.cpp
@@ -542,6 +542,33 @@ void
 				DEBUG_STREAM << "[btntest] RELEASE 0x" << std::hex << s_btnAddr
 					<< std::dec << " at poll " << s_poll << "\n" << std::flush;
 			}
+			// BT_BTNTEST2="addr,pressPoll,releasePoll": an optional SECOND
+			// scripted cycle (e.g. crouch then rise) on the same poll clock.
+			static int s_bt2Addr = -2, s_bt2On = 0, s_bt2Off = 0, s_bt2State = 0;
+			if (s_bt2Addr == -2)
+			{
+				s_bt2Addr = -1;
+				const char *e2 = getenv("BT_BTNTEST2");
+				if (e2 != NULL)
+					sscanf(e2, "%i,%i,%i", &s_bt2Addr, &s_bt2On, &s_bt2Off);
+			}
+			if (s_bt2Addr >= 0)
+			{
+				if (s_bt2State == 0 && s_poll >= s_bt2On)
+				{
+					s_bt2State = 1;
+					EmitButton(s_bt2Addr, 1);
+					DEBUG_STREAM << "[btntest] PRESS2 0x" << std::hex << s_bt2Addr
+						<< std::dec << " at poll " << s_poll << "\n" << std::flush;
+				}
+				else if (s_bt2State == 1 && s_poll >= s_bt2Off)
+				{
+					s_bt2State = 2;
+					EmitButton(s_bt2Addr, 0);
+					DEBUG_STREAM << "[btntest] RELEASE2 0x" << std::hex << s_bt2Addr
+						<< std::dec << " at poll " << s_poll << "\n" << std::flush;
+				}
+			}
 		}
 	}
 
diff --git a/game/reconstructed/btl4vid.cpp b/game/reconstructed/btl4vid.cpp
index 0049583..acc581e 100644
--- a/game/reconstructed/btl4vid.cpp
+++ b/game/reconstructed/btl4vid.cpp
@@ -558,6 +558,11 @@ HierarchicalDrawComponent*
 		//
 		if (segment->IsSiteSegment() /* [0x10] */ != 0)
 		{
+			if (getenv("BT_TREE_LOG"))
+				DEBUG_STREAM << "[tree] SITE seg=" << segment->GetIndex()
+					<< " name=" << (segment->GetName() ? (const char *)segment->GetName() : "?")
+					<< " parent=" << (segment->GetParent() ? segment->GetParentIndex() : -1)
+					<< "\n" << std::flush;
 			// The authentic COCKPIT EYEPOINT.  Built for the true inside view
 			// AND for the player's chase build (buildDebugChaseCamera), so the
 			// V-key toggle can switch to it -- the pod's only view was this
@@ -678,6 +683,14 @@ HierarchicalDrawComponent*
 		// the JointSubsystem's joint table.
 		//
 		int segment_slot = segment->GetIndex() /* [0xcc] */;
+		// DIAG (BT_TREE_LOG): the built joint topology -- segment slot, name,
+		// joint index/type, parent -- the crouch root-drop chain hunt.
+		if (getenv("BT_TREE_LOG"))
+			DEBUG_STREAM << "[tree] seg=" << segment_slot
+				<< " name=" << (segment->GetName() ? (const char *)segment->GetName() : "?")
+				<< " joint=" << segment->GetJointIndex()
+				<< " parent=" << (segment->GetParent() ? segment->GetParentIndex() : -1)
+				<< "\n" << std::flush;
 		Joint *this_joint = NULL;
 		Joint::JointType joint_type;
 		if (segment->GetJointIndex() /* [0xc0] */ == -1)
diff --git a/game/reconstructed/mech2.cpp b/game/reconstructed/mech2.cpp
index 6323e5b..93f5bf8 100644
--- a/game/reconstructed/mech2.cpp
+++ b/game/reconstructed/mech2.cpp
@@ -530,6 +530,8 @@ Scalar
 		return 0.0f;
 	// slot10 state 2 (0x4a6b37): SetLevel(1).
 	case 2:
+		if (getenv("BT_DUCK_LOG"))
+			DEBUG_STREAM << "[duck] squat clip parked (case 2 -> leg alarm 1)\n" << std::flush;
 		m->legStateAlarm.SetLevel(1); return 0.0f;
 	// slot2 (0x4a6b21) + slot1 state 32 (0x4a6b4d) + slot9 state 4 (0x4a6d6e): SetLevel(0).
 	case 3: case 4: case 8: case 9: case 20: case 21:
diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index 9fe16da..5357ded 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -4435,6 +4435,27 @@ void
 						<< " squat=" << squatCapable << ")\n" << std::flush;
 				duckState = 0;							// consumed (@0x4aa0a9)
 			}
+
+			// DIAG (BT_DUCK_LOG, 1 Hz): live joint sample -- does the parked
+			// crouch HOLD at the JOINT level?  Discriminates render-side loss
+			// from a hidden joint writer (the crouch-hold hunt).
+			if (getenv("BT_DUCK_LOG"))
+			{
+				static Scalar s_duckProbe = 0.0f;
+				s_duckProbe += dt;
+				if (s_duckProbe >= 1.0f)
+				{
+					s_duckProbe = 0.0f;
+					JointSubsystem *duckJs = GetJointSubsystem();
+					Joint *knee = (duckJs != 0) ? duckJs->GetJoint(11) : 0;
+					Joint *root = (duckJs != 0) ? duckJs->GetJoint(0)  : 0;
+					DEBUG_STREAM << "[duck] probe legLvl=" << (int)legStateAlarm.GetLevel()
+						<< " j11=" << (knee ? (float)knee->GetHinge().rotationAmount : -99.0f)
+						<< " j0ty=" << ((root && root->GetJointType() == Joint::BallTranslationJointType)
+							? (float)root->GetTranslation().y : -99.0f)
+						<< "\n" << std::flush;
+				}
+			}
 		}
 
 		{
diff --git a/scratchpad/night12/duckmp.sh b/scratchpad/night12/duckmp.sh
new file mode 100644
index 0000000..d55bff5
--- /dev/null
+++ b/scratchpad/night12/duckmp.sh
@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# SEARCHLIGHT bench 2 (external spot cone + replication): night 2-node.
+# A walks to 40u of B and stands (facing B).  B presses the searchlight button
+# (BT_BTNTEST 0x14) at poll 300.  B's lightState replicates (subsystem record
+# 0x14) -> A's replicant Searchlight LightOn flips -> A's TickSearchlight shows
+# the spot.bgf cone on B's mech.
+# PASS: A log "[spot] searchlight pass: ... (external: spot cone)" for B's mech
+# + "[spot] cone SHOWN (seg N)" after B's press; A BT_SHOT frames brighten near
+# B post-toggle.  B log: "[light] ... requested ON" + lightState 0 -> 1.
+set -x
+. /c/git/bt411/scratchpad/night6/bench_common.sh
+cd /c/git/bt411/content || exit 1
+bt_assert_player_env
+taskkill //F //IM btl4.exe > /dev/null 2>&1
+sleep 2
+rm -f duckmp_a.log duckmp_b.log duckmp_relay.log duckmpA_*.png
+bt_expert_egg MP.EGG SG4.EGG
+sed -i "s/^map=.*/map=grass/; s/^time=.*/time=night/; s/^vehicle=.*/vehicle=madcat/" SG4.EGG
+
+(
+  export BT_BTNTEST=0x13,900,960 BT_DUCK_LOG=1
+  export BT_FIRE_LOG=1 BT_FOG_LOG=1 BT_DEATH_LOG=1 BT_MP_LOG=1
+  bt_launch duckmp_b.log SG4.EGG 0x0C -net 1601
+)
+sleep 2
+(
+  export BT_GOTO=enemy BT_GOTO_STOP=40 BT_KEY_NOFOCUS=1 BT_DUCK_LOG=1
+  export BT_SHOT_EVERY=60 BT_SHOT_PREFIX=duckmpA
+  export BT_FIRE_LOG=1 BT_FOG_LOG=1 BT_MP_LOG=1
+  bt_launch duckmp_a.log SG4.EGG 0x03 -net 1501
+)
+sleep 5
+python ../tools/btconsole.py SG4.EGG 127.0.0.1:1501 127.0.0.1:1601 > duckmp_relay.log 2>&1 &
+RELAY=$!
+sleep 90
+kill $RELAY 2>/dev/null
+taskkill //F //IM btl4.exe > /dev/null 2>&1
+sleep 3
+echo "=== B (lamp owner):"
+grep -aE "\[light\]|btntest|\[spot\]" duckmp_b.log | head -8
+echo "=== A (observer -- cone events):"
+grep -aE "\[spot\]" duckmp_a.log | head -8