Every knob the code reads is in the documented file

A sweep of every getenv() in the tree against the environ.ini template
found five options the code answers to that the file never mentioned:
the physics trace, the spawn-zone pin, the gauge profiler, the renderer
diagnostic and the joystick-scan log. They were deliberately env-only
once - scaffolding, not settings - but scaffolding that cannot be found
is scaffolding that gets rebuilt, and RP412RENDERDIAG had already been
forgotten thoroughly enough that this sweep is what rediscovered it.

They get their own section, between the shipped configuration and the
optional extras, with the header saying what they are for: making a
claim about the game testable instead of arguable. All five ship
commented out, cost nothing when off, and none belongs in a real race.

The sweep now closes empty - there is no environment variable the game
reads that the file does not document - and the mention-check keeps it
honest from here: a build that grows a new option names it in rpl4.log
for every carried-over file.

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

RP_L4/RPL4ENVIRON.cpp

@@ -267,6 +267,43 @@ namespace
 "# the old arrival-time behaviour if you want to compare.\n"
 "#RP412NETCLOCK=0\n"
 "\n"
+"# ---- Test harness -----------------------------------------------------------\n"
+"\n"
+"# The knobs that make a run repeatable and measurable. All are off\n"
+"# unless set and cost nothing when off; none belongs in a real race.\n"
+"# They exist so a claim about the game can be tested instead of argued.\n"
+"\n"
+"# Dump the gauge profile to rpl4.log every N seconds: every cockpit\n"
+"# display with its rate mask and tier, how often it ran and what it\n"
+"# cost. This is the engine's own ProfileReport, which was only ever\n"
+"# reachable from the arcade RIO mapper's F11 before.\n"
+"#RP412GAUGEPROFILE=8\n"
+"\n"
+"# 1 = log renderable construction and what each frame is made of, so a\n"
+"# model that never got built can be told from one that is simply out\n"
+"# of shot.\n"
+"#RP412RENDERDIAG=1\n"
+"\n"
+"# 1 = trace the player pod's position to rpl4.log on the SIMULATION's\n"
+"# own clock, stopping the pod dead at the green light so every run\n"
+"# starts from rest. Two runs of the same race then compare sample for\n"
+"# sample - this is the instrument that proved RP412PHYSICSHZ plays the\n"
+"# same race at every frame rate, bit for bit.\n"
+"#RP412PHYSTRACE=1\n"
+"\n"
+"# Try this drop zone first at spawn instead of a random pick. The pick\n"
+"# is seeded by RANDOM=, but a seed only repeats a run if the same\n"
+"# NUMBER of draws comes before the pick, and that count rides on load\n"
+"# timing - so pin the pad too, or two 'identical' runs start over\n"
+"# different ground. Falls back to the random walk if the zone is\n"
+"# taken, so it cannot wedge.\n"
+"#RP412SPAWNZONE=3\n"
+"\n"
+"# 1 = log the XInput-class controllers the generic-joystick scan skips\n"
+"# (attached DirectInput devices are always logged). For debugging a pad\n"
+"# that answers twice or a stick that does not answer at all.\n"
+"#RP412JOYLOG=1\n"
+"\n"
 "# ---- Optional ---------------------------------------------------------------\n"
 "\n"
 "# RGB keyboard lamp mirror (Windows Dynamic Lighting): keys bound to\n"