Cockpit: 1920x1080 single-window MFD arrangement (L4MFDSPLIT=1, RP412 layout)

The RP412 single-window cockpit, adapted to reuse BT's working D3D
surface compositor (DrawDevSurface) instead of RP's GDI child-window
panes -- same visual outcome, far lower risk (no L4VIDEO present-routing
rewrite):

- L4VB16.cpp: kBTCockpitSurfaces places the six instrument surfaces at
  RP412's exact 1920x1080 fractional positions (Heat=UL, Mfd2=UC,
  Comm=UR, Mfd1=LL, Mfd3=LR, radar=center-bottom portrait);
  BTDrawGaugeSurfaces parameterized by surface table; BTDrawCockpitPanel
  composites them over the full-window 3D as the pod bezels frame the
  viewscreen. Hooked in L4VIDEO before EndScene (L4MFDSPLIT-gated).
- btl4main.cpp: L4MFDSPLIT sizes the window to the 1920x1080 canvas
  (scaled to fit the work area; -res overrides) and wakes the gauge
  renderer (L4GAUGE) + PAD controls.

Fixed two more pre-existing latent gauge crashes that only fire when the
gauge renderer is woken off-pod (would hit the real pod too), previously
gated only on BT_DEV_GAUGES -- extended the safety nets to L4MFDSPLIT:
  * gauge.h: NULL gauge-attribute-source binds a static zero instead of
    AV'ing in GaugeConnectionDirectOf ctor (crashed building HeatSink
    cluster's VertTwoPartBar at ConfigureForModel).
  * GAUGE.cpp: SEH-guarded gauge Execute (disable a faulting gauge, not
    crash). GAUGREND.cpp: skip unresolved primitives + activate all MFD
    pages so every surface renders.

Verified: L4MFDSPLIT boots the cockpit; all six surfaces render framing
the 3D viewscreen; survives coolant-loop + gauge activation.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

engine/MUNGA_L4/L4VB16.cpp

@@ -299,14 +299,51 @@ static const BTGaugeSurfaceDesc kBTGaugeSurfaces[6] =
 	{ "Comm", 0xFFFF, 1000.0f / kBTPanelW, 0.0f,   320.0f / kBTPanelW, 0.5f, 0 },
 };
 
+//
+// SINGLE-WINDOW COCKPIT (L4MFDSPLIT=1) -- the RP412 arrangement: the 3D
+// viewscreen fills the whole window and the six instrument surfaces frame it
+// like the pod's bezels (they occlude the corners of the main display by
+// design).  Positions are fractions of a 1920x1080 canvas, matching RP412's
+// SVGA16 split layout (top row of three MFDs, bottom corners, radar centered
+// on the bottom edge):
+//   [ Heat  ][      ][ Mfd2 ][      ][ Comm ]   <- top row (3D shows between)
+//   [ Mfd1 ]   [   radar (portrait)   ]   [ Mfd3 ]
+// BT's five mono MFDs + the palette radar map onto RP's UL/UC/UR/LL/LR + map.
+//
+static const float kMfdW = 320.0f / 1920.0f;		// 0.16667
+static const float kMfdH = 240.0f / 1080.0f;		// 0.22222
+static const float kRadW = 324.0f / 1920.0f;		// 0.16875
+static const float kRadH = 432.0f / 1080.0f;		// 0.40000
+static const BTGaugeSurfaceDesc kBTCockpitSurfaces[6] =
+{
+	{ "Heat", 0xFFFF, 0.0f,                       0.0f,               kMfdW, kMfdH, 0 }, // UL
+	{ "Mfd2", 0xFFFF, (1.0f - kMfdW) * 0.5f,      0.0f,               kMfdW, kMfdH, 0 }, // UC
+	{ "Comm", 0xFFFF, 1.0f - kMfdW,               0.0f,               kMfdW, kMfdH, 0 }, // UR
+	{ "Mfd1", 0xFFFF, 0.0f,                       1.0f - kMfdH,       kMfdW, kMfdH, 0 }, // LL
+	{ "Mfd3", 0xFFFF, 1.0f - kMfdW,               1.0f - kMfdH,       kMfdW, kMfdH, 0 }, // LR
+	{ "sec",  -1,     (1.0f - kRadW) * 0.5f,      1.0f - kRadH,       kRadW, kRadH, 1 }, // radar, bottom center
+};
+
+// L4MFDSPLIT: the single-window cockpit (RP412's flag).  Distinct from the
+// dev-gauge dock (BT_DEV_GAUGES) -- here the 3D fills the window and the
+// surfaces frame it, rather than a strip below a restricted world viewport.
+static bool DevCockpitPanel()
+{
+	static int v = -1;
+	if (v < 0) v = (getenv("L4MFDSPLIT") != NULL) ? 1 : 0;
+	return v != 0;
+}
+
 //
 // Composite ALL SIX gauge surfaces into the CURRENT render target, tiled within the
 // panel rect (px,py,pw,ph).  Reaches the ONE shared SVGA16 via any resolvable port and
 // extracts each surface by its own bit-plane mask.  Ports that don't resolve are skipped.
 //
-void BTDrawGaugeSurfaces(LPDIRECT3DDEVICE9 device, float px, float py, float pw, float ph)
+void BTDrawGaugeSurfaces(LPDIRECT3DDEVICE9 device, float px, float py, float pw, float ph,
+						 const BTGaugeSurfaceDesc *surfaces = 0)
 {
 	if (device == NULL) return;
+	if (surfaces == NULL) surfaces = kBTGaugeSurfaces;
 	GaugeRenderer *gr = application ? application->GetGaugeRenderer() : NULL;
 	if (gr == NULL) return;
 
@@ -347,7 +384,7 @@ void BTDrawGaugeSurfaces(LPDIRECT3DDEVICE9 device, float px, float py, float pw,
 
 	for (int i = 0; i < 6; i++)
 	{
-		const BTGaugeSurfaceDesc &d = kBTGaugeSurfaces[i];
+		const BTGaugeSurfaceDesc &d = surfaces[i];
 		L4GraphicsPort *port = static_cast<L4GraphicsPort*>(gr->GetGraphicsPort(d.portName));
 		if (port == NULL) continue;		// this surface's port isn't configured -> skip
 		// Secondary-CRT unrotation direction is env-flippable (BT_GAUGE_SEC_ROT=3
@@ -406,6 +443,26 @@ void BTDrawGaugeInset(LPDIRECT3DDEVICE9 device)
 	BTDrawGaugeSurfaces(device, 2.0f, 400.0f, 540.0f, 540.0f / 2.75f);
 }
 
+//
+// SINGLE-WINDOW COCKPIT (L4MFDSPLIT=1): the 3D fills the whole window; frame
+// it with the six instrument surfaces at the RP412 arrangement (kBTCockpitSurfaces),
+// composited OVER the world as the last draw before EndScene.  The world pass
+// runs at the FULL viewport in this mode (no strip carve-out), so the surfaces
+// occlude the corners like the pod bezels.  Called from L4VIDEO alongside the
+// dev-gauge inset; the two modes are mutually exclusive.
+//
+void BTDrawCockpitPanel(LPDIRECT3DDEVICE9 device)
+{
+	if (!DevCockpitPanel() || device == NULL) return;
+	IDirect3DSurface9 *rt = NULL;
+	if (FAILED(device->GetRenderTarget(0, &rt)) || rt == NULL) return;
+	D3DSURFACE_DESC d;
+	rt->GetDesc(&d);
+	rt->Release();
+	BTDrawGaugeSurfaces(device, 0.0f, 0.0f, (float)d.Width, (float)d.Height,
+		kBTCockpitSurfaces);
+}
+
 //===========================================================================//
 // DEV-COMPOSITE -- the SEPARATE cockpit-MFD window (the default under BT_DEV_GAUGES).
 // A second top-level window fed by an ADDITIONAL SWAP CHAIN on the existing main