Closed the loop: BT_CRIT_PROBE=8 on solo DEV.EGG drove the full per-zone FX chain
end-to-end -- [zonefx] entity 1:321 seg 12 psfx 12/13 -- proving TakeDamage ->
mechdmg effect loop -> BTStartZoneEffect -> StartEntityEffectImplementation (segment
world-pos resolve) -> BTStartPfxAttached fires live. The 2-node fight harness didn't
engage (mechPicks=0, an MP-harness spawn/connect issue, not FX); BT_CRIT_PROBE is the
reliable solo liveness path.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>