Lunar Porter, rung three and a half: fuel

Every thruster costs a unit every tick it fires, so holding two at once
costs two - the honest price, and it makes a drift you corrected expensive
in a way a drift you avoided is not.

AN EMPTY TANK IS NOT AN ENDING. There is no message and nothing stops: a
lander with no fuel is still flying, it just cannot do anything about
where. What happens next is gravity, and gravity is patient. The test for
it holds the thruster from the first frame to the last and crashes anyway,
which is what says the fuel is real - a lander that could hold Up for ever
would land every time, and the economy this is the first half of would
have nothing to buy.

The gauge is in the window, which is what the window was built for two
commits ago: a bar at a SCREEN position, so the moon turning underneath
does not carry it off. Thirty five cells after a label, redrawn whole
every frame because seventy bytes out of one port is cheaper than working
out which of them changed.

A byte of fuel, and a byte is enough. Over eight it is a bar of up to
thirty one cells - a shift, because there is no divide - and at a unit a
thruster a tick it is about forty seconds of holding the engine open.
Sixteen bits would be more arithmetic for a number nobody reads to the
unit.

Cargo and the bases are the other half.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Tests/manifest

@@ -1033,6 +1033,16 @@ cosmosLanderSoft     | CosmOS/Source/cosmos.asm           | run      | -
 # nought; the front end hands out the numbers the host gave it, so reading only the first
 # works on the machine it was written on and silently does nothing on the next one.
 cosmosLanderPadOne   | CosmOS/Source/cosmos.asm           | run      | -                  | 60000000 | disks/cosmos.img | lander.keys | landerIdle.pad,landerSoft.pad
+# ---- A tank runs out, and gravity is patient ----
+#
+# The thruster is held from the first frame to the last and it still crashes. Fuel is a byte
+# and a thruster costs one a tick, so about forty seconds of holding the engine open empties
+# it - and an empty tank is not an ending, it is a lander that is still flying and can no
+# longer do anything about where.
+#
+# Which is what says the fuel is real. A lander that could hold Up for ever would land every
+# time, and the whole economy this is the first half of would have nothing to buy.
+cosmosLanderDry      | CosmOS/Source/cosmos.asm           | run      | -                  | 40000000 | disks/cosmos.img | lander.keys | landerBurn.pad
 # ---- And the thing that says whether a controller is being seen at all ----
 #
 # Three states look identical from inside a game that is not responding: a pad the front end