CosmOS lets every voice go when a program stops

A gate is a register on the sound device and only a program can drop one.
A program that has stopped cannot: it is gone. So a note left held
sustained until something else said otherwise, and nothing else did -
one program could leave the machine sounding for as long as it ran, with
nothing the person at it could do.

The shell already puts back the Stack, the vectors, the drive, the
working directory and the screen. This is the same list and the same
argument, and the fault path calls it too, for the stronger version of
the argument: a program that CRASHED is exactly the one that cannot tidy
up after itself, and a machine that will not stop humming is a poor place
to read an error message.

It does not make the device silent at once and does not pretend to.
Dropping a gate RELEASES a note rather than stopping it, so the patch's
release still runs. A bounded tail rather than an endless one is the part
the system can be responsible for without knowing what instrument the
program had built.

Hum exits while holding a note; Pause makes no sound and takes a couple
of million cycles, because the machine stops the moment the shell runs
out of input and a note quietened at that instant leaves no samples
behind to say whether it was. They are on a disk of their own so that a
fixture does not move the ten recordings that quote cosmos.img's listing.

THE CHECK CAUGHT ITSELF PASSING WRONGLY FIRST. Pause was missing from the
disk, the machine halted immediately, and the window that should have
held the tail was past the end of a render a twentieth of a second long -
an empty window's peak is nought, which is indistinguishable from silence.
So the sample count is asserted before anything is read from it. Verified
with break.sh: without the call the note is still ringing at 9869.

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

Programs/CosmOS/Source/cosmos.asm

@@ -1496,6 +1496,10 @@ faultSay:
   ; read, and a program that faulted may have left the screen with nowhere to put a letter.
   CALL faultScreen
 
+  ; And quiet, before them. A program that faulted mid-note left one sounding and is no longer
+  ; in a position to stop it.
+  CALL soundQuiet
+
   CALL printString
   SETD.1 FaultNumbered
   LDA.1
@@ -5154,6 +5158,40 @@ screenGiveDone:
 screenGiveNone:
   RET
 
+; ---- Every voice let go of ----
+;
+; The same argument as the screen, and for a stronger reason. A program that took the sound
+; device and stopped has nothing left that could end a note it was holding: a gate is a
+; register on the device and only a program can drop one. A held note sustains until somebody
+; says otherwise, so what this bounds is the difference between a machine that rings for a
+; moment and one that rings until it is switched off.
+;
+; IT DOES NOT MAKE THE DEVICE SILENT AT ONCE, and does not pretend to. Dropping a gate
+; RELEASES a note rather than stopping it, so whatever release the patch was given still runs.
+; A bounded tail rather than an endless one is the part the system can be responsible for
+; without knowing what instrument the program had built.
+;
+; A PROGRAM THAT FAULTS CANNOT TIDY UP AFTER ITSELF, which is why this is called from the
+; fault path too. A machine that will not stop humming is a poor place to read an error
+; message, and the program that would have quietened it is exactly the one that just died.
+;
+; Safe from a fault handler: four port writes, no service, no disk, and nothing that can
+; refuse.
+soundQuiet:
+  RSTA
+soundQuietOne:
+  OUTA 0x41                 ; This channel. Every sound port writes to whichever was last.
+  PSHA
+  RSTA
+  OUTA 0x45                 ; Let go of whatever it was holding.
+  POPA
+  INCA
+  INIB 0d4
+  CCF
+  SUB
+  BNQ soundQuietOne
+  RET
+
 ; The registers a console cannot work without, put back. Not the picture - that is
 ; screenGive's, and only happens for a program that asked.
 screenSane:
@@ -6266,6 +6304,10 @@ handleExit:
   ; What was on the screen before this program had it, if it asked for that.
   CALL screenGive
 
+  ; And every voice let go of, for the same reason the screen is: a program that has stopped
+  ; cannot drop a gate it left up.
+  CALL soundQuiet
+
   ; The drive the person was on, whatever the program did with it.
   PSHA
   SETD.1 RunDrive