Authentic target acquisition LIVE: reticle slew + pick-ray lock + aimed zone damage (task #36)

The engine Reticle model (MUNGA/RETICLE.h [T0]) reconstructed end to end:
- Mech::targetReticle is a real Reticle member bound to the TargetReticle
  attribute (0x1d), per the RP VTV analog (VTV.h targetReticle).
- Crosshair slew: mouse -> client rect -> reticle coords (the pod stick
  free-aim channel's dev-box stand-in); BT_AIM="x y" pins it headless.
  LMB fires lasers / RMB missiles (alongside SPACE/CTRL).
- Pick ray: the ACTIVE eye publishes pos + LookAtRH basis (BTSetAimCamera,
  L4VIDRND view-write site) + the render loop publishes proj._22;
  BTGetAimRay builds the world ray, Mech::PickRayHit slab-tests it against
  the collision template's ExtentBox via the engine's BoundingBox::HitBy
  (local frame; clips the Line at entry) -> world hull point.
- Designation: the mech under the crosshair designates (sticky; re-hover
  refreshes; cleared when the target leaves the roster at burial); the
  entity target slots 0x37c/0x388/0x38c feed the whole weapon path.
- Aimed fire: while HOT the impact point is the PICKED hull point -> the
  STEP-6 cylinder lookup resolves the zone under the crosshair (verified:
  center-aim -> head-band zone 13 dominant). Off-crosshair the sticky
  designation converges on center mass.
- HUD: the aim group draws at the slewed position ([0x9a] translate,
  contained by push/pop); the designator ring tracks the target's
  projected point (subB9 hot / subB8 designated, BTProjectToReticle);
  edge arrows when off-screen/behind.
- AUTHENTIC gating: no fire arc exists in the binary (FireWeapon fires
  whenever HasActiveTarget, part_013.c:7758) -> BT_FIRE_ARC is now an
  explicit OPT-IN presentation clamp; the hardwired gEnemyMech lock and
  the projectile path's gEnemyMech fallback are removed.
- Fixed en route: every renderable rebuild stomped mCamera back to the
  chase eye (start-inside silently lost the cockpit camera; the aim feed
  exposed it). BTL4VideoRenderer::mViewInside persists the chosen view.

Verified headless: BT_AIM="0 0" -> HOT lock, pick hits the hull face at
exact range, aimed zones resolve; BT_AIM="0.8 0.3" -> no lock, zero
damage, zero missile launches; kill chain completes to wreck + smoke.

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

context/decomp-reference.md

@@ -159,6 +159,10 @@ The authentic stack is DEFAULT-ON (`BTEnvOn`, mechrecon.hpp): `BT_GAIT_CUTOVER`,
 | `BT_SECTOR_LOG` | SectorDisplay Make/Execute |
 | `BT_NET_TRACE` | `[net-tx]/[net-rx]/[net-upd]` MP tracing |
 | `BT_DEV_GAUGES` | render the 6 pod MFD surfaces in a separate dev window |
+| `BT_AIM="x y"` | pin the reticle crosshair (reticle coords) — headless aim harness |
+| `BT_AIM_LOG` | `[pick]` ray/box/hit diagnostics (Mech::PickRayHit) |
+| `BT_FIRE_ARC=<deg>` | OPT-IN external-camera fire-arc clamp (unset = authentic no-arc) |
+| `BT_START_INSIDE` | begin in the cockpit view (V toggles) |
 
 Full render/locomotion gates (BT_RAMP, BT_MATPRI, BT_CULL, BT_SHADOW_*, BT_LODSEL, BT_ADDLOD,
 BT_PUNCH, …) are catalogued in [[rendering]].