Toolchain: VS2022 (v143) is the build of record -- /FORCE:UNRESOLVED retired

The v143 linker refuses to emit an image with unresolved externals even
under /FORCE, so the dead offline-tool ladders in mech3.cpp
(Mech::CreateSubsystemStream / SubsystemDefaultData -- never called at
runtime, resources ship prebuilt in BTL4.RES) are compiled out behind
BT412_OFFLINE_TOOLS (default off). The exe links /FORCE:MULTIPLE only:
a genuinely unresolved symbol is now a hard link error instead of a
hidden runtime AV. No other source changes needed for v143.

Verified: clean build; solo DEV.EGG runs; two-instance loopback MP via
btconsole.py -- mesh forms, mission runs both sides, master + replicant
tick in each world. (Phase 1 of docs/BT412-ROADMAP.md)

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

game/reconstructed/mech3.cpp

@@ -96,9 +96,11 @@
 //   Those ~21 classes live in sibling modules not visible here (and PPC /
 //   GaussRifle / SubsystemMessageManager have no reconstructed class at all),
 //   so the uniform factory surface is declared here as minimal stubs.  The
-//   bodies/data are resolved at link against the real subsystem modules; these
-//   declarations only let the dispatch compile.  Kept LOCAL so they never
-//   collide with the real sibling classes.
+//   bodies/data were NEVER reconstructed anywhere -- under v142 the link
+//   left them unresolved and /FORCE tolerated it (the path is dead at
+//   runtime); the v143 linker does not, so the dispatch ladders below are
+//   compiled out unless BT412_OFFLINE_TOOLS is defined.  Kept LOCAL so they
+//   never collide with the real sibling classes if ever reconstructed.
 //===========================================================================//
 typedef Mech::SharedData SharedData;	// namespace-scope alias (== Entity__SharedData)
 
@@ -711,6 +713,20 @@ void
 		NotationFile				*subsystem_file,	// param_8
 		const ResourceDirectories	*directories)		// param_9
 {
+#if !BT412_OFFLINE_TOOLS
+	//-----------------------------------------------------------------------
+	// BT412 NEUTRALIZED (offline authoring path -- never called at runtime;
+	// resources ship prebuilt in BTL4.RES).  The ~21 per-subsystem
+	// CreateStreamedSubsystem statics were never reconstructed, and the
+	// VS2022 (v143) linker fails the image on unresolved externals even
+	// under /FORCE (the v142 linker tolerated them).  The authentic
+	// dispatch ladder is preserved under BT412_OFFLINE_TOOLS for the day
+	// the offline tool path is reconstructed.
+	//-----------------------------------------------------------------------
+	DEBUG_STREAM << "[offline] Mech::CreateSubsystemStream(" << type_name
+		<< ") reached with BT412_OFFLINE_TOOLS off\n" << std::flush;
+	return -1;
+#else
 	int	result;
 
 	if      (Streq(type_name, "HeatSinkClassID"))
@@ -765,6 +781,7 @@ void
 	}
 
 	return (result == 0) ? -1 : 1;
+#endif	// BT412_OFFLINE_TOOLS
 }
 
 
@@ -909,6 +926,8 @@ fail:
 	Mech::SubsystemDefaultData(const char *type_name)
 {
 	if (Streq(type_name, ""))						return &Mech::DefaultData;					// 0050bde4 (DAT_0050dc1f == "")
+#if BT412_OFFLINE_TOOLS	// BT412 NEUTRALIZED with the factory above -- the per-subsystem
+						// DefaultData statics were never reconstructed (no callers at runtime).
 	if (Streq(type_name, "ControlsMapper"))			return &MechControlsMapper::DefaultData;	// 0050ee00
 	if (Streq(type_name, "AmmoBinClassID"))			return &AmmoBin::DefaultData;				// 005125bc
 	if (Streq(type_name, "HeatSinkClassID"))		return &HeatSink::DefaultData;				// 0050e580
@@ -930,6 +949,7 @@ fail:
 	if (Streq(type_name, "GaussRifleClassID"))		return &GaussRifle::DefaultData;			// 00512478 (shares MissileLauncher table)
 	if (Streq(type_name, "ControlsMapper"))			return &MechControlsMapper::DefaultData;	// 0050ee00 (2nd alias)
 	if (Streq(type_name, "MechTech"))				return &MechTech::DefaultData;				// 0050e270
+#endif	// BT412_OFFLINE_TOOLS
 	return 0;
 }