Fold soundThing's changes back down, and expose the two new switches

The three changes that went up came back as part of soundThing, along
with two more that they made possible. The engine here is now b73e5c0
character for character, except that em-dashes and arrows in comments are
written as ASCII because this tree is ASCII only - a local rule, not an
improvement, and not sent up.

So synth.h's "what was changed" list is gone. There is nothing to list:
what has to be kept current is only that if either copy changes, the
other one has to be told.

---- What came back ----

A VOICE CAN END ITSELF. Naming the level's source said what shapes a
voice; nothing said what ends one, so the only thing that could ever
finish one was a key coming up. A game is nearly all one-shots and not
one of them wants its length decided by how long a note was held. Exposed
as parameter 0x51: 0 gated, 1 triggered.

AND A ONE-SHOT IS THE SAME ONE-SHOT TWICE. A triggered voice re-arms its
oscillators, and an LFO can be told to start over with each voice -
parameter 3 of either LFO. Both halves are needed and the check proves
it: with the LFO left free, two triggered hits still differ.

Their note warned that whatever applies a patch to a channel has to set
these or they hold synthInit's defaults. Checked: Voyager never calls
synthSyncVoices, so their 0001 is a no-op here as they predicted, and
nothing reaches into an LFO's phase, so the struct split is safe.

---- What it is for ----

Lander's crash is a triggered voice now, so boomOff is gone. Nothing has
to remember to end a bang.

SoundPatch learnt voice_levelSource, voice_gate and lfo<N>_mode, which
the new soundThing writes - without that it would have refused every
patch saved from it, since an unknown field stops the tool on purpose. A
patch from before those fields still converts, and says in its own
comments that it predates the level routing.

Three checks, each seen to fail on its own break: a gated voice still
sounding with nothing holding it, a triggered one down to nothing with no
gate ever dropped, and two hits identical sample for sample.

One test bug worth keeping: the first version of the repeatability check
struck the second note while the first was still ringing, so what it
found and compared as "the second hit" was a point in the middle of the
first one's tail. It now looks for sound after SILENCE rather than sound
after an offset.

Programs/CosmOS/Apps/Lander.asm

@@ -2537,7 +2537,6 @@ explode:
   CALL startBurst
   CALL boom
   CALL runBurst
-  CALL boomOff
   RET
 
 ; ---- Dust, for a landing that went right ----
@@ -2683,6 +2682,20 @@ putBoom:
   OUTA 0x41                 ; Channel three. Every parameter write below lands on it.
   SETD.0 BoomPatch
   CALL playPatch
+
+  ; ---- Struck, not held ----
+  ;
+  ; A gated voice lasts as long as something keeps hold of it, and the gate coming up is what
+  ; starts its release - which is what a keyboard is. A crash is not a keyboard. It is struck
+  ; once and then plays its own length, and nothing should have to remember to end it.
+  ;
+  ; Said here rather than left to the patch because it is the PROGRAM that knows this is a
+  ; one-shot: the patch decides what the bang sounds like, and this decides that it is a bang.
+  ; A patch designed in soundThing carries a gate of its own, and this overrides it on purpose.
+  INIA 0x51
+  OUTA 0x42
+  INIA 0x01                 ; Triggered.
+  OUTA 0x43
   RET
 
 ; ---- A whole patch, out of a table ----
@@ -2716,14 +2729,6 @@ boom:
   OUTA 0x44                 ; Writing the note is what starts it.
   RET
 
-; And letting go of it, once there is nothing left to watch.
-boomOff:
-  INIA 0x03
-  OUTA 0x41
-  RSTA
-  OUTA 0x45                 ; Dropping the gate is the only thing that ends a note.
-  RET
-
 ; ---- A key, or a button ----
 ;
 ; Somebody flying on a controller should not have to reach for the keyboard to say "yes, I