aimed fire strikes the part under the crosshair: the per-segment pick (#73)

The port's target pick was a whole-mech bounding-box slab test, and every hit
-- aimed or not -- dispatched zone -1 into the victim's cylinder lottery. The
recovered 1995 model (the division-card scene intersection) struck a SEGMENT
and credited that segment's own damage zone. This is the port's equivalent.

At render-tree build, each segment's draw object and its PrimaryDamageZone --
authored per segment in the skeleton stream, read by JMOVER.cpp:290 -- are
recorded in MechRenderTree::segPick. The pick (BTL4VideoRenderer::
MechSegmentPick) ray-tests the per-segment bounding spheres on the live posed
skeleton, using the draw-cached mLocalToWorld (at most one frame stale, fine
for aiming).

Selection is SPECIFICITY-FIRST: among the spheres the ray pierces, the
smallest radius wins, normalized-distance tie-break. Both obvious rules were
measured failing the same way before this one: the torso mesh's sphere
(r~4.1 on the MadCat, vs shoulders at r~1.0) envelops nearly the whole mech,
so its front face is nearest for any aim AND any near-body ray normalizes to
~0 against it. Limb spheres nest inside the envelope; smallest-pierced picks
the most specific part on the aim line, and the torso wins only when no limb
is threaded -- the per-part semantic the pod's mesh test produced.

mech4.cpp tries the segment pick per candidate; the box PickRayHit survives
only as the fallback (no tree yet, wrecked, spectator), still carrying zone
-1 into the lottery, and a structure occlusion clears the zone. The winner's
zone rides MECH_TARGET_SUBIDX + targetReticle.targetDamageZone into
SendDamageMessage, so aimed hits now dispatch a real zone; the victim's
handler applies it directly (bursts 2+ still re-lottery, authentic per the
recovered @0x4a0230 loop).

Bench, the same L/C/R sweep that exposed the bug: aiming left now lands
36/41 hits on zone 2 = jointlshoulder -- the left arm -- with a 0.30 thread
score, where the same aim was a 6-way lottery spray before. The MadCat's
authored segment->zone map is rich (shoulders 2/9, guns 6/17, hip 1, six leg
zones, torso 0). Known approximations, flagged for field verification:
sphere bounds rather than triangles, and a torso-envelope graze credits the
torso where the pod's exact mesh test would have missed into air.

The field protocol is the one the testers already ran on night 6: stationary
mechs, short range, fire only at one arm -- the paper doll should now damage
THAT arm.

Diag: BT_PICK_LOG ([segpick] map at build, [pickwin] per pick).

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

context/decomp-reference.md

@@ -473,6 +473,7 @@ default-ON (`'0'` disables).
 | `BT_SELF_DAMAGE=<dps>` | dispatch an unaimed `TakeDamage` at your OWN mech once a second, through the real `Entity::Dispatch` path, so the whole RESPAWN family is bench-testable solo (nothing else can kill the local pilot: `BT_MP_FORCE_DMG` only targets replicants). **Latches off at first death** so everything after the respawn is the respawn's doing, not the harness still shooting you |
 | `BT_POWER_DETACH_TEST=<name\|1>` | drop a subsystem's voltage link + force Auto, so the auto-hunt must recover it. `1` = first powered subsystem to tick; a NAME (`PPC_1`, `Myomers`) targets one, which is what proves FAILOVER to a different generator rather than a same-generator re-attach |
 | `BT_AUDIO_SOURCES=<n>` | request `n` OpenAL mono sources instead of the driver default (~256). **Opt-in on purpose** — the cap doubles as a governor, and with EFX reverb live a higher ceiling means more simultaneous voices mixing during heavy combat. Measure frame time. See [[wintesla-port]] |
+| `BT_PICK_LOG` | #73 aimed-pick diagnostics: `[segpick]` the segment→zone map at tree build (index, name, zone, sphere), `[pickwin]` the winning zone/score/t per pick (score ~0 = threading the part core, ~1 = envelope graze) |
 | `BT_CRIT_LOG` | #80 crit diagnostics: `[subarmor]` per-subsystem armour/scales/critBonus at ctor (proves the resource keys parsed + the zone got REAL scales), `[critroll]` per landed crit (zone, subsystem, its resulting own-zone level). NB the type-0x1e loader's `[crit]` tag is a different, older log |
 | `BT_DEVICELOST_TEST=<frame>[,crashrepro]` | #35 bench hook. `<frame>` forces the D3D9 DEVICELOST branch at that render frame (+600/+1200 = 3 cycles), driving the REAL `BTResetLostDevice` recovery. `,crashrepro` runs the field null-teardown shape (double `ParticleEngine::Destroy`) — pre-fix this reproduced the field crash byte-for-byte (`Destroy +0x11`, `target=0x0`); post-fix it must log `SURVIVED`. See [[wintesla-port]] §Device-loss |