4.10 reconstruction: real spawn factory path -> Mech ctor frontier

BTPlayer::CreatePlayerVehicle reconstructed (faithful; BT411's BT_SPAWN_XZ/
BT_SPAWN_ENEMY bring-up scaffolding dropped): builds the Mech::MakeMessage from
the mission game-model resource and hands it to MakeAndLinkViewpointEntity.
Mech::Make = new Mech(creation_message); a staged Mech ctor chains the real
JointedMover base (so the model skeleton/segments stream from BTL4.RES) then
Fails.

This validates the entire spawn factory chain live: CreatePlayerVehicle ->
MakeAndLinkViewpointEntity -> registry -> Mech::Make -> new Mech -> JointedMover
base ctor (streams the mech model) -> halts at the Mech ctor (mech.cpp:66).

The Mech ctor (@004a1674, 5690 bytes -- the largest function in the game) plus
the subsystem roster is the next MAJOR milestone, not a brick: it needs the full
1995 Mech member layout derived first (MECH.HPP is still reserved[331]; BT411's
decomp uses raw offset pokes that can't compile fresh), the subsystem class
hierarchy (only GAUSS/PPC/SENSOR survive in the 4.10 archive; the rest are the
measured "917 missing functions"), and the segment-table walk. Plan + scope in
MECH.NOTES.md.

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

restoration/source410/BT/BTPLAYER.CPP

@@ -39,6 +39,22 @@
 #	include <dropzone.hpp>
 #endif
 
+#if !defined(MECH_HPP)
+#	include <mech.hpp>
+#endif
+
+#if !defined(RESOURCE_HPP)
+#	include <resource.hpp>
+#endif
+
+#if !defined(HOSTMGR_HPP)
+#	include <hostmgr.hpp>
+#endif
+
+#if !defined(MISSION_HPP)
+#	include <mission.hpp>
+#endif
+
 //
 //#############################################################################
 // Shared data support
@@ -278,14 +294,68 @@ void
 
 //
 //#############################################################################
-// Vehicle creation -- pulls in the Mech subsystem (Mech::Make), not yet
+// CreatePlayerVehicle  Build the player's mech from the mission game-model
-// reconstructed.  This is the current boot frontier.
+// resource and bind it as the viewpoint entity.  (An observer player gets a
+// MUNGA camera ship from the base Player::CreatePlayerVehicle instead.)
+//
+// Constructs the Mech::MakeMessage and hands it to MakeAndLinkViewpointEntity,
+// which routes through the registry to Mech::Make -> the Mech ctor (the mech
+// subsystem, not yet reconstructed -- current boot frontier).
 //#############################################################################
 //
 void
-	BTPlayer::CreatePlayerVehicle(Origin)
+	BTPlayer::CreatePlayerVehicle(Origin mech_location)
 {
-	Fail("BTPlayer::CreatePlayerVehicle -- btplayer.cpp not yet reconstructed");
+	Check(this);
+	Check(application);
+
+	ResourceFile *resources = application->GetResourceFile();
+	Check(resources);
+	Check_Pointer(playerMission->GetGameModel());
+
+	HostManager *host_manager = application->GetHostManager();
+	Check(host_manager);
+
+	//
+	// Make any MUNGA-level vehicle (a camera ship for an observer player).
+	//
+	Player::CreatePlayerVehicle(mech_location);
+
+	//
+	// If the player still has no vehicle, build him a mech and link to it.
+	//
+	if (!playerVehicle)
+	{
+		ResourceDescription *mech_res =
+			resources->FindResourceDescription(
+				playerMission->GetGameModel(),
+				ResourceDescription::ModelListResourceType
+			);
+		Check(mech_res);
+		mech_res->Lock();
+
+		Mech::MakeMessage
+			create_player(
+				Mech::MakeMessageID,
+				sizeof(Mech::MakeMessage),
+				EntityID(host_manager->GetLocalHostID()),
+				(Entity::ClassID)MechClassID,
+				EntityID::Null,
+				mech_res->resourceID,
+				Mech::DefaultFlags,
+				mech_location,
+				Motion::Identity,
+				Motion::Identity,
+				playerMission->GetBadgeName(),
+				playerMission->GetColorName(),
+				((BTMission *)playerMission)->GetPatchName()
+			);
+
+		mech_res->Unlock();
+
+		playerVehicle = application->MakeAndLinkViewpointEntity(&create_player);
+		Register_Object(playerVehicle);
+	}
 }
 
 void

restoration/source410/BT/MECH.CPP

@@ -43,10 +43,31 @@ Mech::SharedData
 //#############################################################################
 //
 Mech*
-	Mech::Make(MakeMessage *)
+	Mech::Make(MakeMessage *creation_message)
+{
+	return new Mech(creation_message);
+}
+
+//
+//#############################################################################
+// Mech ctor -- the heart of the entity (walks the model segment table and
+// instantiates the full subsystem roster: power, heat, weapons, actuators,
+// controls, tech, damage zones).  This is the largest single function in the
+// game and the current reconstruction frontier; see MECH.NOTES.md.  Chains to
+// the JointedMover base so the skeleton/segments stream before it Fails.
+//#############################################################################
+//
+Mech::Mech(
+	MakeMessage	*creation_message,
+	SharedData	&shared_data
+):
+	JointedMover(creation_message, shared_data)
+{
+	Fail("Mech::Mech -- mech.cpp not yet reconstructed");
+}
+
+Mech::~Mech()
 {
-	Fail("Mech::Make -- mech.cpp not yet reconstructed");
-	return NULL;
 }
 
 void

restoration/source410/BT/MECH.NOTES.md

@@ -0,0 +1,68 @@
+# MECH.CPP / .HPP — reconstruction notes
+
+**Status: `Mech::Make` (factory) reconstructed; the Mech constructor and the
+entire mech subsystem are the CURRENT FRONTIER — the largest remaining
+milestone in the reconstruction.**
+
+## What is reconstructed
+
+- `Mech::Make(MakeMessage *)` = `return new Mech(creation_message);` — the
+  factory the registry / `MakeAndLinkViewpointEntity` calls.
+- The static shared data (ClassDerivations / DefaultData) — from the earlier
+  staging.
+- A staged Mech ctor that chains the real `JointedMover` base ctor (so the
+  model skeleton/segments stream from BTL4.RES) and then Fails.
+
+The spawn factory path is now validated live: `BTPlayer::CreatePlayerVehicle`
+builds the `Mech::MakeMessage`, `Application::MakeAndLinkViewpointEntity` routes
+it through the registry to `Mech::Make` -> `new Mech` -> the JointedMover base
+ctor (real engine code, streams the mech model) -> the Mech ctor Fail. Boot
+reaches `mech.cpp:66`.
+
+## Why the Mech ctor is a milestone, not a brick
+
+`Mech::Mech` is `@004a1674`, **5690 bytes** — the largest single function in the
+game. It walks the model's segment table and instantiates the full subsystem
+roster (power, heat, weapons, actuators, controls, tech, damage zones), and
+primes ~150 members. Reconstructing it requires three things the tree does not
+yet have:
+
+1. **The complete 1995 Mech member layout as named fields.** MECH.HPP currently
+   carries `int reserved[331]` (1324 bytes) as a placeholder. BT411's Ghidra
+   reconstruction sidesteps the layout entirely by writing raw offset pokes
+   (`Wword(0x104)`, `*(void**)((char*)this + 0x388)`, `this[0x14a]`) — a
+   WinTesla-port technique that CANNOT compile into a fresh 1995 build, where
+   BC4.52 assigns offsets from the header declarations. So the layout must be
+   derived as real members first.
+2. **The subsystem class hierarchy.** MechSubsystem + derived: sensor, generator
+   (gnrator), gyro, torso, HUD, myomers, plus the weapon subsystems (mechweap,
+   ppc, gauss, projweap, mislanch, ammobin...). Of these, only GAUSS, PPC,
+   SENSOR survive as source in the 4.10 archive (CODE/BT/BT); GNRATOR is a
+   partial .TCP. The rest are part of the measured "917 missing functions" and
+   come only from BT411's decomp.
+3. **The segment-table walk** that reads the model resource and instantiates +
+   wires each subsystem.
+
+BT411's mech reconstruction is ~12,255 lines across mech.cpp / mech2 / mech3 /
+mech4 / mechsub alone, before the subsystem TUs — this is the bulk of the
+remaining game.
+
+## Reconstruction plan (for the dedicated mech milestone)
+
+1. **Derive the Mech member layout.** Turn `reserved[331]` into named members.
+   Sources: BT411's offset comments (`this[0x14a]` gyroSubsystem, `+0x388`
+   target entity, etc.) give the binary offsets; the embedded member types
+   (NameFilter, AlarmIndicator, Slot/Socket, Reticle, Filter, CString,
+   StateIndicator) come from the surviving MUNGA headers. Cross-check total size
+   against the binary's `new Mech` allocation.
+2. **Reconstruct MechSubsystem base + the subsystem roster**, backdating BT411
+   mechsub.cpp + the per-subsystem TUs; fold in the surviving 4.10 GAUSS/PPC/
+   SENSOR source where it exists (authoritative over the decomp).
+3. **Reconstruct the Mech ctor** against the named layout: embedded-member
+   construction, the segment-table walk, subsystem instantiation + wiring.
+4. Then the per-frame path (mech2 animation SM, mech3, mech4 locomotion/
+   targeting) and the damage/weapon handlers.
+
+Until then the ctor Fails cleanly at the frontier; everything below it (engine,
+app, network, mission, player, factory, jointed-mover base) runs real
+reconstructed code.