Make the screen come back on the machine people actually run

Found by running it: Grid exits and the shell prints its prompt into the
grid, with the view up to seven pixels out of alignment. Three faults, and
the first is the one that made the other two visible.

MAKE RUN-VOYAGER HAD NO SCRATCH DRIVE. It gives drive 1 to Disks/personal.img,
which is a file and not volatile, so there was nowhere to keep a screen -
osTakeScreen answered no and the whole feature silently did not happen. It
was tested with --ram-disk and shipped without one, which is as good a
description of testing the wrong machine as I can write. There is now a RAM
disk in drive 2, after the personal disk so that drive 1 stays the one that
is yours.

A PROGRAM TOLD NO MUST COPE. A refusal is not a fault, it means doing what
the program did before there was anywhere to save a screen. Grid deleted
its own tidying up when it started asking, so being refused left the grid
on screen with a prompt written into it. It clears up again when refused,
and only then.

AND THE SYSTEM ALWAYS LEAVES THE SCREEN USABLE. The fine scroll registers
go back to zero at every program exit, whether or not the picture could be
saved: the console draws in whole cells, so a view three pixels into one
puts every character three pixels out for ever. That is not part of saving
a screen and should never have depended on it.

Both paths are checked now. With a scratch drive the screen comes back cell
for cell; without one, no grid is left behind. Breaking either fails one of
them and not the other.

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

Programs/CosmOS/Source/cosmos.asm

@@ -2090,6 +2090,14 @@ screenGiveDone:
 screenGiveNone:
   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:
+  RSTA
+  OUTA 0x37
+  OUTA 0x38                 ; No fraction of a cell in either direction.
+  RET
+
 ; Video memory as bank 4, which is what makes it reachable at all. Bank 3 is the disk's; see
 ; the table in the CosmOS README, which exists because a program once took 3.
 screenBank:
@@ -3072,6 +3080,16 @@ handleExit:
   SETD.1 LastStatus
   STA.1
 
+  ; ---- The screen made usable, whether or not the picture can be given back ----
+  ;
+  ; A fraction of a cell is never what anybody wants left behind: the console draws in whole
+  ; cells, so a view three pixels into one puts every character three pixels out for ever.
+  ; That is true whether or not there was anywhere to save the picture, so it is not part of
+  ; the saving - a program refused by osTakeScreen still must not leave the shell squinting.
+  ;
+  ; Before screenGive, so that a restored screen's own registers win.
+  CALL screenSane
+
   ; What was on the screen before this program had it, if it asked for that.
   CALL screenGive