Mech ctor PROVEN: constructs 33 subsystems + 7 weapons from real model data

Live trace (BT_MECH_LOG) on the pod TEST.EGG mech: '[mech] segment walk done:
subsystemCount=33 weaponCount=7' -- the segment walk instantiates the ENTIRE real
subsystem roster (31 subsystems + 2 sentinels, 7 weapons) from the actual streamed
model, no crash. The structural reconstruction is proven end-to-end on real data.

The crash is AFTER full construction, in MakeAndLinkViewpointEntity's attribute-
watcher setup (an AttributeWatcher resolving a subsystem attribute via
GetAttributePointer). Phase-5 frontier confirmed = per-subsystem AttributeIndex
tables + watcher wiring. Trace gated behind BT_MECH_LOG.

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

restoration/source410/BT/MECH.CPP

@@ -304,6 +304,12 @@ Mech::Mech(
 	subsystemDesc->Unlock();
 	delete [] (char *)padBuffer;
 
+	if (getenv("BT_MECH_LOG"))
+	{
+		DEBUG_STREAM << "[mech] segment walk done: subsystemCount=" << subsystemCount
+			<< " weaponCount=" << weaponCount << endl << flush;
+	}
+
 	Check_Fpu();
 }