#84: the replicant salvo now HOMES AT THE LIVE TARGET -- the stale-point double detonation is gone

Oracle (674): "missile appear to register hit explosions twice, once where
target was and again where the target is".  Rajel (693): "once where the mech
was when I fired and on the expected impact".

MECHANISM, measured on two nodes (BT_PROJ_LOG "DET at" now logs EVERY contact
detonation, including damage-0 rounds, which were invisible before): the
replicant salvo mirror pushed rounds with NO entity handle at the FROZEN
fire-time aim point, and the pool's contact test is proximity to p.targetPos --
so mirror rounds "contacted" the empty air where the target USED to be and
detonated there, on every peer, every salvo (45 salvos -> 234 frozen-point
air bursts in a 200s bench).  The true impact appears at the live position
(the shooter's own homing rounds on his node; the victim's damage reaction on
peers) -- two sites per salvo, exactly as reported.

THE BINARY'S MODEL (CLASSMAP, Missile flight-entity cluster): missiles are
ENTITIES with authoritative/GHOST Performance variants (Projectile
PTR_LAB_005129e8 / 005129f4) and their own WriteUpdateRecord (@4bef4c, slot 7)
-- peers ran ghost missiles updated from the wire and saw the TRUE trajectory.
One explosion, correct place, every node.  The frozen-point mirror is the port
infidelity (the entity Missile itself stays blocked by the documented 2007
Entity-base mismatch; mislanch.cpp:301).

FIX: the MissileLauncher update record now carries the locked target's EntityID
(salvoTargetID; EntityID::Null = point fire).  The mirror resolves it on the
receiving node via HostManager::GetEntityPointer (engine T0, an index-socket
Find -- NULL-safe on any ID), refuses non-mechs via BTIsRegisteredMech, and
pushes the mirror rounds WITH the handle -- they re-lead on the live local
replicant exactly as the master's own rounds do, and detonate at the true
position.  Guards: record-length gate (a short record from an older build has
no ID field -- its tail would be garbage and must not resolve) + Null check +
registered-mech check.

VERIFIED (two nodes, 200s, missile autofire both ways):
  * every record arrives len=52/52 with sane aims ([mlrec] diag)
  * 22/46 salvos resolve (tgtID=3:22 -> the victim's local master) and their
    mirror rounds home: the frozen-air DET population fell 234 -> 102, the
    live-homing population rose to 155/207 per node
  * the unresolved remainder is BENIGN and correct: EntityID::Null point fire
    plus hostID=-1 LOCAL entities -- i.e. the victim's WRECK, which autofire
    keeps shooting after the kill; a wreck does not move, so the frozen aim IS
    its true position
Downstream expectations: Ronin's smoke-screen (#114) should drop by ~the mirror
half, and the audio census (#32) loses the duplicate Static3DPatchSource
explosion sounds on peers -- both to be read from the next field logs.

Also in this commit: [projectile] DET diagnostic (every contact detonation with
position/damage/handle/aim), [mlrec] record-arrival diagnostic (len/recID/
subsys/counter/aim, capped 200), scratchpad/night9/mp_double.sh.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scratchpad/night9/mp_double.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# #84: measure the DOUBLE DETONATION on two real nodes.
+#
+# A and B chase and fire missiles at each other.  Every contact detonation now
+# logs position + aim + target handle (BT_PROJ_LOG "DET at").  READ:
+#   * on节点 B, [projectile] REPLICANT salvo lines = A's mirrored fire, aim = the
+#     FROZEN fire-time point; their DETs should land at that frozen point
+#     (tgt=00000000) -- the stale half of the double.
+#   * DETs with tgt!=0 = own homing rounds -> the true impact position.
+#   * matchlog VEHICLE rows give both mechs' positions to measure staleness.
+set -x
+. /c/git/bt411/scratchpad/night6/bench_common.sh
+cd /c/git/bt411/content || exit 1
+bt_assert_player_env
+rm -f mpd_a.log mpd_b.log
+bt_expert_egg MP.EGG MPD.EGG
+
+launch () {   # $1=log $2=affinity $3=port
+  BT_MP_LOG=1 BT_DMG_LOG=1 BT_MATCHLOG=1 BT_PROJ_LOG=1 \
+  BT_GOTO=enemy BT_GOTO_STOP=100 BT_AUTOFIRE=1 BT_AF_MISSILE=1 BT_AF_PERIOD=5 \
+    bt_launch "$1" MPD.EGG "$2" -net "$3"
+  sleep 2
+}
+
+launch mpd_b.log 0x0C 1601
+launch mpd_a.log 0x03 1501
+sleep 5
+python ../tools/btconsole.py MPD.EGG 127.0.0.1:1501 127.0.0.1:1601 &
+PC=$!
+
+sleep 200
+kill $PC 2>/dev/null
+bt_kill_ours
+rm -f MPD.EGG
+echo "=== DONE ==="