diff --git a/restoration/source410/BT/MECH.CPP b/restoration/source410/BT/MECH.CPP
index 37808485..05f0f07c 100644
--- a/restoration/source410/BT/MECH.CPP
+++ b/restoration/source410/BT/MECH.CPP
@@ -100,7 +100,8 @@ const Mech::IndexEntry
 	ATTRIBUTE_ENTRY(Mech, RadarAngularPosition,	radarAngularPosition),
 	ATTRIBUTE_ENTRY(Mech, LinearSpeed,			currentBodySpeed),
 	ATTRIBUTE_ENTRY(Mech, MaxRunSpeed,			reverseStrideLength),
-	ATTRIBUTE_ENTRY(Mech, DuckState,			duckState)
+	ATTRIBUTE_ENTRY(Mech, DuckState,			duckState),
+	ATTRIBUTE_ENTRY(Mech, EyepointRotation,		eyepointRotation)
 };
 
 Mech::AttributeIndexSet
diff --git a/restoration/source410/BT/MECH.HPP b/restoration/source410/BT/MECH.HPP
index 26eacbdd..d6a2fe90 100644
--- a/restoration/source410/BT/MECH.HPP
+++ b/restoration/source410/BT/MECH.HPP
@@ -180,6 +180,16 @@
 			LinearSpeedAttributeID,
 			MaxRunSpeedAttributeID,
 			DuckStateAttributeID,
+			//
+			// The 3-D renderer reads this BY NAME: DPLRenderer::SetupCull
+			// (CODE/RP/MUNGA_L4/L4VIDEO.CPP:4990) fetches
+			// "EyepointRotation" off the viewpoint entity and, for a
+			// JointedMover, composes it with the siteeyepoint segment to
+			// build worldToEyeMatrix.  Without it the engine Fails every
+			// frame.  The member already existed -- only the publication
+			// was missing.
+			//
+			EyepointRotationAttributeID,
 			NextAttributeID
 		};
 
diff --git a/restoration/source410/BT_L4/BTL4VID.CPP b/restoration/source410/BT_L4/BTL4VID.CPP
index 1c9c27aa..d292f74b 100644
--- a/restoration/source410/BT_L4/BTL4VID.CPP
+++ b/restoration/source410/BT_L4/BTL4VID.CPP
@@ -36,8 +36,41 @@ BTL4VideoRenderer::~BTL4VideoRenderer()
 {
 }
 
+//
+//#############################################################################
+// LoadMissionImplementation -- called by Renderer::LoadMission (the authentic
+// engine, CODE/RP/MUNGA/RENDERER.CPP:263) after it has set
+// LoadingRendererStatus, stamped nextRenderTime and started the renderer with
+// the RendererManager.  This is where a GAME renderer builds the mission's
+// scene content on the Division board.
+//
+// BRING-UP NO-OP (phase 1 of the btl4vid ladder).  A no-op is a LEGAL body
+// here, not a cheat: the engine's own VideoRenderer::LoadMissionImplementation
+// (CODE/RP/MUNGA/VIDREND.CPP:259) is a bare Tell, and our GaugeRenderer
+// (GAUGREND.CPP:3275) ships the same.  The renderer therefore comes up and
+// runs its frame loop with an EMPTY scene, which is exactly what we want to
+// measure before writing any content.
+//
+// THE AUTHENTIC SHAPE, pinned by the surviving sibling header for Red
+// Planet's renderer (CODE/RP/RP_L4/RPL4VID.HPP -- same engine, same board,
+// same year; only the .CPP is missing there too):
+//
+//     LoadMissionImplementation walks the mission's entities and calls
+//     MakeEntityRenderables(entity, model_resource, view_type) for each,
+//     which builds a dpl_DCS hierarchy through ReadSKLFile /
+//     RecurseSKLFile (the skeleton notation pages), with a material
+//     substitution list set up around it.
+//
+// The BT-specific renderables (BTReticleRenderable, BTTranslocationRenderable,
+// the pending-wrecks map) come from the BT411 donor game/reconstructed/
+// btl4vid.cpp -- 3188 lines -- but NOTE that port restructured this hook and
+// has no method under this name, so the CONTRACT above comes from the 1995
+// engine and only the CONTENT comes from the donor.
+//#############################################################################
+//
 void
 	BTL4VideoRenderer::LoadMissionImplementation(Mission *)
 {
-	Fail("BTL4VideoRenderer::LoadMissionImplementation -- btl4vid.cpp not yet reconstructed");
+	Check(this);
+	Tell("BTL4VideoRenderer::LoadMissionImplementation -- empty scene (bring-up)\n");
 }
diff --git a/restoration/source410/RENDER-ROADMAP.NOTES.md b/restoration/source410/RENDER-ROADMAP.NOTES.md
index fff94e62..c93589bd 100644
--- a/restoration/source410/RENDER-ROADMAP.NOTES.md
+++ b/restoration/source410/RENDER-ROADMAP.NOTES.md
@@ -134,3 +134,46 @@ MakeVideoRenderer returns NULL unless DPLARG is set (BTL4APP.CPP:152), and no
 gauge conf sets it -- so no video renderer exists in those runs at all.  That
 frame was almost certainly attract/loading art out of BTL4.RES.  The evidence
 above is the real thing, and it came from setting DPLARG deliberately.
+
+--------------------------------------------------------------------------------
+TWO RUNGS CLIMBED -- the 3-D pipeline now runs end to end to the geometry load
+--------------------------------------------------------------------------------
+RUNG 1: BTL4VideoRenderer::LoadMissionImplementation, Fail -> bring-up no-op.
+A no-op is a LEGAL body, not a cheat: the engine's own
+VideoRenderer::LoadMissionImplementation (CODE/RP/MUNGA/VIDREND.CPP:259) is a
+bare Tell, and our working GaugeRenderer (GAUGREND.CPP:3275) ships the same.
+The renderer comes up and runs its frame loop with an EMPTY scene, which is
+what we wanted to measure before writing content.
+
+RUNG 2: Mech::EyepointRotation PUBLISHED.  With the renderer live the engine
+immediately Failed at
+
+    l4video.cpp(5004): DPLRenderer::SetupCull jointed mover had no
+                       EyepointRotation attribute
+
+SetupCull (CODE/RP/MUNGA_L4/L4VIDEO.CPP:4990) fetches "EyepointRotation" BY
+NAME off the viewpoint entity and, for a JointedMover, composes it with the
+"siteeyepoint" segment to build worldToEyeMatrix.  Our mech already HAD
+EulerAngles eyepointRotation with a getter (MECH.HPP) -- only the attribute
+publication was missing.  One enum id + one table row.  (The siteeyepoint
+check passed first time, so that segment was already streaming correctly.)
+
+WHERE IT STOPS NOW, and why that is not a defect:
+
+    L4VIDEO.cpp couldn't load object buttee.bgf   (x123, also dg100/mslr)
+    NULL instance
+
+ZERO Fails, zero exceptions -- the run reaches the full mech build (all 7
+weapons), constructs the renderer, boots the board (~907K VPX wire
+transactions), loads the mission, runs the per-frame cull and gets all the way
+into geometry loading.  The models ARE present (VIDEO/GEO/BUTTEE.BGF etc, 879
+BGFs) and BTDPL.INI points at them (objectpath=.ideo\geo), but loading a
+.BGF goes through the board to the EXTERNAL GL render bridge that the VPX HLE
+tees over VPX_FIFOSOCK -- and that bridge was not running.  "NULL instance"
+comes from the prebuilt LIBDPL.LIB, i.e. the library refusing to instance an
+object that never loaded.
+
+NEXT RUNG: run under the documented full rig (render-bridge/launch_pod.ps1,
+see LAUNCH.md) so the bridge is up and geometry actually loads.  Only then is
+it worth writing real MakeEntityRenderables content -- until the bridge is in
+the loop there is nothing to see even if the scene graph is correct.