# MECHSUB — reconstruction notes (phase 2 kickoff, 2026-07-19)

**Status: base-class ANALYSIS done; the reconstruction must be done FRESH against
the 4.10 structure, NOT backdated from BT411 (its base class + damage model
diverge). Key findings below de-risk the actual code.**

MechSubsystem is the base of the ~30-class subsystem roster (sensor, gyro, torso,
hud, generator, myomers, weapons…) the Mech ctor's segment-table walk
instantiates. The staged MECHSUB.HPP is interface-only (one `Mech *owner`
member, no bodies). Reconstructing the base is phase-2 step 1.

## Dependencies (all survive in the 4.10 archive)

- `Subsystem` (CODE/RP/MUNGA/SUBSYSTM.HPP) — the base.
- `DamageZone` (CODE/RP/MUNGA/DAMAGE.HPP/.CPP) — the engine damage zone.
- `Mech__DamageZone : public DamageZone` (CODE/BT/BT/MECHDMG.HPP) + the BT damage
  model (MechCriticalSubsystem, redirect tables, critical hits).
- `AlarmIndicator` (just reconstructed, MUNGA/ALARM.HPP) — statusAlarm.

## Finding 1 — the base Subsystem DECLARES the zone but does NOT create it (RESOLVED)

SUBSYSTM.HPP:181 declares `DamageZone *damageZone;` in the **base** Subsystem and
its TakeDamage (SUBSYSTM.HPP:177-178) delegates `damageZone->TakeDamage(damage)`.
The base ctors ARE reconstructed — **staged source410/MUNGA/SUBSYSTM.CPP** (built,
in munga.lib; 38 Subsystem:: syms in the map). Both base ctors set
`damageZone = NULL` (resource ctor line 63) — the base does **not** allocate the
zone. So the DERIVED MechSubsystem creates the `Mech__DamageZone` (BT411's
zone-creation is structurally right here) — but the ARMOUR it seeds must follow
Finding 2 (per-type streamed), not BT411's per-facing hand-seed.

## Finding 2 — CRITICAL: the damage model diverged

The 4.10 base DamageZone (DAMAGE.HPP/CPP) is a **per-damage-TYPE** model:
- members: `defaultArmorPoints` (Scalar) + `damageScale[Damage::DamageTypeCount]`
  where DamageTypeCount = 5 = {Collision, Ballistic, Explosive, Laser, Energy}.
- TakeDamage: `damageLevel += damage.damageAmount * damageScale[damage.damageType]`
  (DAMAGE.CPP:413); the zone STREAMS its own armour (`*stream >> defaultArmorPoints;
  *stream >> damageScale[ii]`, DAMAGE.CPP:335,340).

BT411's reconstruction is a **per-FACING** model: `armorByFacing[5]` (front/back/
left/right/top) + `structureReference`, **manually seeded** by MechSubsystem's
resource ctor with an armour→absorption-coefficient inversion. Those field names
(`armour[5]`, `structureReference`) exist only in BT411's `ReconDamageZone`
proxy — NOT in the surviving 4.10 DamageZone/Mech__DamageZone. The staged
`MechSubsystem__SubsystemResource` (armorByFacing[5]+structureReference) was
copied from BT411 and is likewise suspect for 4.10.

**Consequence:** BT411's MechSubsystem ctor (heat.cpp/mechsub.cpp) CANNOT be
backdated verbatim — it would install a damage model the 4.10 engine's DamageZone
doesn't implement, corrupting every subsystem's damage behaviour. The 4.10
MechSubsystem must let the base Subsystem + DamageZone stream ctor handle armour
(per-type), not hand-seed per-facing values.

## Corrected reconstruction approach (fully scoped — ready to write)

1. ~~Pin the base Subsystem ctor~~ **DONE (Finding 1)** — staged SUBSYSTM.CPP sets
   `damageZone = NULL`; MechSubsystem creates the `Mech__DamageZone`.
2. Reconstruct MechSubsystem: chain the base Subsystem, `new Mech__DamageZone(this,
   index)`, add the mech-specific members (statusAlarm = AlarmIndicator, vital
   flag, alarmModel, criticalReference, collisionCriticalHitWeight,
   printSimulationState, configureActivePress) and the TakeDamage override, using
   the 4.10 **per-type** damage model — let the zone stream its own armour
   (defaultArmorPoints + damageScale[5]); do NOT hand-seed BT411's per-facing
   armorByFacing[5]/structureReference.
3. Re-derive `MechSubsystem__SubsystemResource` against the 4.10 DamageZone stream
   format (the staged struct's per-facing fields are BT411-copied and suspect).
4. Then the roster (GAUSS/PPC/SENSOR source + .TCP partials + decomp).

Analysis complete; step 2 is the next code to write. This worksheet is the
deliverable that keeps the subsystem foundation on the 4.10 damage model rather
than BT411's divergent one.