gauges: secondary/radar MFD composites live on a dev box (Milestone B)

The pod's secondary/radar cockpit surface now renders as an inset in the
800x600 dev window under BT_DEV_GAUGES: radar/tactical grid, SPEED/HEADING/
MAGNETIC/PROP dials, and the color-coded ARMOR DAMAGE mech schematic -- real
gauge content (nzSec=27247), composited from the shared CPU pixelBuffer.

Composite pass (engine): SVGA16::DrawDevInset palette-expands the secondary
plane into a MANAGED texture on the MAIN device and draws an XYZRHW inset quad;
BTDrawGaugeInset() reaches the gauge renderer's 'sec' port and is called from
DPLRenderer::ExecuteImplementation as the last draw before EndScene.

Three reconstruction bugs fixed to get real content:
1. BTL4Application::MakeGaugeRenderer signature mismatch (REAL fix): the
   reconstructed no-arg override only HID the 2007-engine's widened 3-arg
   virtual MakeGaugeRenderer(int*,int*,int*), so the engine built a base
   L4GaugeRenderer whose ctor never parsed gauge/l4gauge.cfg -> empty symbol
   table -> "undefined label 'bhk1Init'" -> no ports/gauges. Matched the 3-arg
   signature so it truly overrides (args ignored; BT is fullscreen). Same bug
   class as the BTL4GaugeRenderer(false,NULL,NULL,NULL) ctor fix.
2. Parse hung on undefined primitives (gated dev accommodation): the BT gauge
   primitive table (BTL4MethodDescription) is still a stub, so an unknown
   primitive -> ReportParsingError -> Fail() -> a MODAL dialog freezing the
   parse. Under BT_DEV_GAUGES, skip the unknown primitive's params so labels
   register and the base "configure" primitive builds the ports.
3. Gauge widgets AV on NULL data bindings (gated): NumericDisplayScalar's NULL
   value_pointer -> GaugeConnectionDirectOf ctor deref (bind NULL->static zero);
   RankAndScore::Execute derefs unreconstructed game state (Gauge::GuardedExecute
   SEH wrapper -> Disable(True) on first fault).

All guards gated on BT_DEV_GAUGES: default DEV un-regressed (TARGET DESTROYED,
0 crashes) and the pod path is byte-unchanged (strict Fail, no guards).

Remaining (docs/GAUGE_COMPOSITE.md): the real gauge WIDGET reconstruction
(BTL4MethodDescription method table + gauge->game-state data bindings), then
Step 2 (RP<->BT MFD port-name reconcile) + Step 3 (2-window layout).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -645,6 +645,36 @@ so a forced L4GAUGE on non-pod hardware degrades cleanly; (3) **pod main-view fu
 pod's 800×600 main monitor, but pod fullscreen-on-a-chosen-adapter is a Phase-8 detail). The Phase-4 HUD/MFD
 render work now targets the profile's LOGICAL surfaces, not a hardcoded single window.
 
+**✅✅ GAUGE DEV-COMPOSITE — the pod's SECONDARY/RADAR MFD renders LIVE on a dev box (opt-in `BT_DEV_GAUGES`;
+full map + findings in `docs/GAUGE_COMPOSITE.md`).** The FOLLOW-UP (1) above is DONE for the secondary surface:
+an inset in the bottom-left of the 800×600 window shows the authentic BT cockpit secondary MFD — **radar/
+tactical grid** (SCALE/SECTOR + crosshair), **SPEED/HEADING/MAGNETIC/PROP dials**, and the color-coded
+**ARMOR DAMAGE mech schematic** (green intact / red damaged) — REAL content (`nzSec=27247` non-zero pixels).
+The draw model is CPU-raster→texture-upload, DEVICE-INDEPENDENT: gauge widgets raster 16-bit R5G6B5 into ONE
+shared `Video16BitBuffered::pixelBuffer`; `SVGA16::DrawDevInset` (L4VB16.cpp) palette-expands the secondary
+plane into a MANAGED texture on the MAIN device + draws an `XYZRHW|TEX1` inset quad; `BTDrawGaugeInset(mDevice)`
+is called from `DPLRenderer::ExecuteImplementation` as the last draw before `EndScene`. **THREE recon bugs
+fixed to get real content (1 genuine fix + 2 gated dev accommodations):** (a) **⭐ `BTL4Application::
+MakeGaugeRenderer` SIGNATURE MISMATCH** — the reconstructed no-arg override only HID the 2007-engine's widened
+3-arg virtual `MakeGaugeRenderer(int*,int*,int*)` (APP.cpp:382), so the engine built a BASE `L4GaugeRenderer`
+whose ctor never calls `BuildConfigurationFile` → `gauge\l4gauge.cfg` was NEVER PARSED → `undefined label
+'bhk1Init'` → no ports. FIXED to the 3-arg signature (args ignored; BT is fullscreen). Same bug class as the
+`BTL4GaugeRenderer(false,NULL,NULL,NULL)` ctor fix — recon written to the ORIGINAL signature vs the WIDER 2007
+virtual. (The gauge label = `GetGameModel()`+`"Init"`=`bhk1Init`; CFG has `Bhk1Init` but the symbol lookup is
+`stricmp`, so case is irrelevant — the table was just empty. `MechInit`, CFG:4390, is the shared macro that
+builds the sec/overlay/Mfd/Heat/Comm PORTS via the base `configure` primitive.) (b) **parse HUNG on undefined
+primitives** — `BTL4MethodDescription` (btl4grnd.cpp) is a STUB (BT gauge widget classes unreconstructed), so
+an unknown primitive → `ReportParsingError`→`Fail()`→a MODAL dialog freezing mid-parse; gated skip
+(GAUGREND.cpp) walks past the unknown primitive's params so labels register + base `configure` builds the
+ports. (c) **gauge widgets AV on NULL data bindings** — `NumericDisplayScalar` value_pointer NULL →
+`GaugeConnectionDirectOf` ctor deref (bind NULL→static zero, gauge.h); `RankAndScore::Execute` derefs
+unreconstructed game state (`Gauge::GuardedExecute` SEH wrapper → `Disable(True)` on first fault). All gated
+`BT_DEV_GAUGES`; **default DEV (no gauges) un-regressed (TARGET DESTROYED, 0 crashes) + pod path byte-unchanged**
+(strict `Fail`, no guards). **REMAINING = the real gauge WIDGET reconstruction:** the `BTL4MethodDescription`
+method table (BT gauge classes: `PlayerStatus` + ~16 recovered `methodDescription` entries) + the gauge→
+game-state DATA BINDINGS (why some gauges resolve NULL) — that is what the dev skip/guards stand in for, and
+what the POD needs. Then Step 2 (RP↔BT MFD port-name reconcile → the 5 MFDs) + Step 3 (2-window layout).
+
 **Alternate route considered:** run original `btrel410.exe` under DOSBox — **blocked**: it needs the
 VPX/IG board DOSBox can't emulate; bypassing it = the shim work anyway.