radar: composite the OVERLAY plane -- SECTOR/SCALE were blank on every desktop path

Playtester DOS-binary comparison: our radar showed blank SECTOR:/SCALE: values.
Root cause [T1]: the secondary CRT's low byte is authored as TWO ports
(L4GAUGE.CFG:4395-4396) -- sec (0x3F, btspal) + overlay (0xC0, btopal,
TransparentZero) carrying the btsec1ov graticule, the SCALE numeral
(RadarRange) and the SECTOR numerals (sectorDisplay).  Both numeral writers
are reconstructed and RUN -- their pixels were in the shared buffer's 0xC0
bits all along -- but every desktop expand indexed the LUT with pixel & 0x3F,
stripping them.  The arcade DAC indexed the FULL low byte.

Key mechanism: clut0 ALREADY holds the DAC's combined 256-entry table --
BuildSecondaryPalette (AllChannels, sec) fills all 256 indices and the
overlay's TransparentZero pass overwrites groups 0x40/0x80/0xC0 -- so the
composite is exactly a mask change, no blending code:

  - BTSecCompositeMask(): sec->GetBitMask() | overlay's (NULL-guarded, same
    display), used by BTDrawGaugeSurfaces + BTDrawCockpitPanels (surround),
    SVGA16::Update case 0 (pod parity), and the glass BlitSurface palette
    expand.
  - GlassWindowToken: the palette-expanded radar window's dirty token now
    includes the overlay port -- the SECTOR numerals tick on that plane, and
    a pixel-only 0x3F token would never repaint them.

The overlay's ColorMapper re-stomp over combined indexes is authentic (the
shipped machine ran the identical palette code) and is left alone.

Verified live (glass panels): SECTOR: 497.503 ticking with movement,
SCALE: 1000 at spawn (radarRange init 250*2^2 -- the DOS reference's 4000 is
max zoom, not a delta), and the btsec1ov graticule rules now draw.  KB:
GAUGE_COMPOSITE row 28 + polish list updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/GAUGE_COMPOSITE.md

@@ -217,7 +217,7 @@ yet reconstructed (parse-skipped). The separate window is now the **live viewer*
 - **Pod MFD port-name reconcile (pod-only):** a ~5-line positional dual-name fallback in `SVGA16::Update`
   (`UL = GetGraphicsPort("auxUL2"); if(!UL) UL = GetGraphicsPort("Heat"); …`) so BT MFDs reach the pod's real
   monitors. NOT a CFG rename (the CFG uses BT names pervasively + `MUNGA_L4` is shared with RP's aux names).
-- **Polish:** overlay-plane compositing over `sec`; a pod-accurate RGB-packing toggle; texture atlas
+- **Polish:** ~~overlay-plane compositing over `sec`~~ (DONE 2026-08-13, row 28); a pod-accurate RGB-packing toggle; texture atlas
   (one lock/upload); device-reset recreate hardening for the additional swap chain.
 
 ## Widget reconstruction — the real fix (in progress; mapped by `bt-gauge-widget-recon-map`)
@@ -691,7 +691,7 @@ reconfigure/externalConfigure); parse-skip list EMPTY ([gskip]=0), all 50 attr b
 | 25 | sec: headingPointer needle + numeric | YawPitchRoll decomposition (engine-convention port of euler[0]) | LIVE: 089→120 while turning under BT_GOTO | T2 | CORRECT |
 | 26 | sec: numericSpeed | LinearSpeed (abs(adv)/dt) | LIVE: 0 parked → 176-182 walking | T2 | CORRECT (units question stays open) |
 | 27 | sec: digitalClock MISSION TIME | engine mission clock (format enum arg) | LIVE: 09:19→06:04 counting | T0/T2 | CORRECT |
-| 28 | sec: sectorDisplay (overlay) | localOrigin → Round(−Z·0.01)+500 / Round(X·0.01)+500 | commit 4a4ec68 [BT_SECTOR_LOG live]; NOTE: overlay plane not composited into the dev sec cell (polish item) — data verified by log | T2 | CORRECT |
+| 28 | sec: sectorDisplay (overlay) | localOrigin → Round(−Z·0.01)+500 / Round(X·0.01)+500 | commit 4a4ec68 [BT_SECTOR_LOG live]; **overlay plane COMPOSITED 2026-08-13** (branch sec-overlay-composite): every sec expand (BTDrawGaugeSurfaces, BTDrawCockpitPanels, SVGA16::Update case 0, glass BlitSurface) now uses sec\|overlay = 0xFF — clut0 already held the arcade DAC's combined table (BuildSecondaryPalette spreads each port over the other's bit combos), so the fix is mask-only; the glass dirty token gained the overlay port so the numerals repaint. Verified live: SECTOR ticks + SCALE:1000 at spawn (1000 = radarRange init; the DOS shot's 4000 is max zoom) + the btsec1ov graticule now draws | T2 | CORRECT |
 | 29 | sec: schematic ARMOR view (cmArmor/multiArmor, dama.pcc) | zone damageLevel ×100 → adpal ramp | incr.3/4; all-green pristine LIVE | T2 | CORRECT (AUTH-STATIC all-green solo) |
 | 30 | sec: schematic CRITICAL view (cmCrit) | subsystem simulationState/damage | LIVE this audit: N-cycle shows the full subsystem list (GEN A-D, LOOP 1-6, HUD, SENSORS, GYRO, TORSO, weapons) | T2 | CORRECT |
 | 31 | sec: schematic HEAT view (cmHeat) | subsystem currentTemperature tint | #6 pixel-verified; re-cycled this audit (mask 0x450421→0x490421→0x510421) | T2 | CORRECT |

engine/MUNGA_L4/L4GLASSWIN.cpp

@@ -1313,6 +1313,20 @@ static void
 	int mask = port->GetBitMask();
 	int palId = port->paletteID;
 	int tint = w->monoTint;
+	// OVERLAY COMPOSITE (2026-08-13): the radar's low byte is TWO ports -- sec
+	// (0x3F) + overlay (0xC0: the graticule art, the SCALE numeral and the
+	// SECTOR numerals).  The arcade DAC indexed the full low byte and clut0
+	// already holds the combined 256-entry table (BuildSecondaryPalette spreads
+	// each port over the other's bit combinations), so the palette-expanded
+	// window composites both planes with just the OR'd mask -- previously the
+	// 0x3F mask left SECTOR:/SCALE: blank while their writers were live.
+	if (tint < 0)
+	{
+		L4GraphicsPort *ov =
+			static_cast<L4GraphicsPort*>(gr->GetGraphicsPort("overlay"));
+		if (ov != NULL && ov->graphicsDisplay == port->graphicsDisplay)
+			mask |= ov->GetBitMask();
+	}
 	static int sMfdPal = -1;
 	if (sMfdPal < 0) sMfdPal = getenv("BT_GLASS_MFD_PAL") ? 1 : 0;
 	if (sMfdPal && tint >= 0)
@@ -2110,6 +2124,11 @@ static unsigned long
 		const char *ports[8];
 		int np = 0;
 		ports[np++] = w->portPrimary;
+		if (w->monoTint < 0)
+			ports[np++] = "overlay";	// composited into the palette-expanded
+										// radar (2026-08-13) -- the SECTOR/SCALE
+										// numerals tick on THIS plane, so their
+										// churn must mark the window dirty
 		if (w->portAlt != NULL) ports[np++] = w->portAlt;
 		for (int gi = 0; gi < w->groupCount && np < 7; ++gi)
 		{

engine/MUNGA_L4/L4VB16.cpp

@@ -860,6 +860,31 @@ static const float kBTPanelH = 480.0f;
 // channel-enabled and which is BlankColor; the draw loop below skips the
 // blanked plane, so the dev cell shows exactly what the pod monitor shows.
 // The Eng entries share their sibling's cell rect and FOLLOW it in the list.
+//
+// OVERLAY COMPOSITE (2026-08-13).  The secondary CRT's low byte is authored as
+// TWO ports -- sec (bits 0x3F, btspal) and overlay (bits 0xC0, btopal,
+// TransparentZero) carrying the graticule art, the SCALE numeral (RadarRange)
+// and the SECTOR numerals (sectorDisplay).  The arcade DAC indexed the FULL low
+// byte, blending both planes; every port expand used to mask to sec's 0x3F,
+// which is why SECTOR:/SCALE: read blank on desktop while their reconstructed
+// writers were live in the buffer the whole time.  clut0 already holds the
+// DAC's combined 256-entry table (BuildSecondaryPalette spreads each port's
+// colors across the other's bit combinations), so the composite is exactly
+// this mask -- no blending code.
+//
+static int BTSecCompositeMask(GaugeRenderer *gr, L4GraphicsPort *sec_port)
+{
+	int mask = sec_port->GetBitMask();
+	if (gr != NULL)
+	{
+		L4GraphicsPort *ov =
+			static_cast<L4GraphicsPort*>(gr->GetGraphicsPort("overlay"));
+		if (ov != NULL && ov->graphicsDisplay == sec_port->graphicsDisplay)
+			mask |= ov->GetBitMask();
+	}
+	return mask;
+}
+
 static const BTGaugeSurfaceDesc kBTGaugeSurfaces[9] =
 {
 	{ "Heat", 0xFFFF,    0.0f / kBTPanelW, 0.0f,   320.0f / kBTPanelW, 0.5f, 0 },
@@ -946,7 +971,9 @@ void BTDrawGaugeSurfaces(LPDIRECT3DDEVICE9 device, float px, float py, float pw,
 			rot = s_secRot;
 		}
 		svga->DrawDevSurface(
-			device, i, port->GetBitMask(), port->paletteID, d.monoTint,
+			device, i,
+			d.monoTint < 0 ? BTSecCompositeMask(gr, port) : port->GetBitMask(),
+			port->paletteID, d.monoTint,
 			px + d.cellX * pw, py + d.cellY * ph, d.cellW * pw, d.cellH * ph, rot);
 	}
 
@@ -1322,7 +1349,9 @@ void BTDrawCockpitPanels(LPDIRECT3DDEVICE9 device)
 				}
 				int surf     = ckSlotOf[i];
 				int useTint  = (d.monoTint < 0) ? -1 : tint;
-				svga->DrawDevSurface(device, i, port->GetBitMask(), port->paletteID, useTint,
+				int useMask  = (d.monoTint < 0) ? BTSecCompositeMask(gr, port)
+				                                : port->GetBitMask();
+				svga->DrawDevSurface(device, i, useMask, port->paletteID, useTint,
 					(float)L.surfX[surf], (float)L.surfY[surf], (float)L.surfW[surf], (float)L.surfH[surf], rot);
 			}
 		}
@@ -5833,7 +5862,7 @@ Logical SVGA16::Update(Logical forceAll)
 		//Drawing secondary, make sure we got secondary
 		if (secPort != NULL)
 		{
-			secMask = secPort->GetBitMask();
+			secMask = BTSecCompositeMask(renderer, secPort);	// sec | overlay (DAC parity)
 			secPalette = &((SVGA16 *) secPort->graphicsDisplay)->palette[secPort->paletteID];
 		} else
 		{