Breakpoints: SWI osBreak, and s refuses a read only bank

A breakpoint that shows every register as the program had them, waits for a
key, and carries on.

NOTHING IS OVERWRITTEN, and that is the design rather than a shortcut. A
breakpoint poked into a running program has to replace an instruction, and
putting that instruction back in order to continue is the same act as
disarming the breakpoint; firing a second time would mean stepping over the
restored instruction and putting the breakpoint back behind it, and this
machine cannot step a single instruction. SWI is two bytes, dispatches
through a vector, and its frame already holds the address after it, so RETI
resumes at the next instruction with nothing to restore and nothing to
re-arm. It fires every time it is reached.

The price is that a breakpoint is part of the program: a build with them in
has different addresses from a build without. That is the bargain every
machine with a break instruction makes.

Every value shown comes out of the frame rather than the registers, because
by the time the handler runs the registers are the handler's. Apps/Break.asm
stops twice so that the second stop is checked as well as the first.

Also here, found by the test that came with it: the monitor's s wrote into
whichever bank was selected, and bank 2 is the controller's own table,
published read only. Writing to it was refused, and a refusal nobody catches
stops the machine - so selecting the bank table to look at it and then typing
s killed the session. bankPresent now keeps the whole flags byte and s
declines. The recorded output of cosmosMonitor had contained that crash,
having been blessed without being read.

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

Tests/expected/cosmosBreak.out

@@ -0,0 +1,16 @@
+CosmOS
+> loaded, starting at 2000
+> two stops, and what the registers were at each
+break at 200E
+A 11 B 22 Q 00 S 00 
+DP0 1030 DP1 05CC DP2 039A DP3 2000 
+press a key 
+break at 2018
+A 44 B 55 Q 00 S 00 
+DP0 1000 DP1 05CC DP2 039A DP3 2000 
+press a key 
+carried on to the end
+finished
+> halted
+Execution halted.
+[exit 0]

Tests/expected/cosmosMonitor.out

@@ -26,6 +26,35 @@ CosmOS
 0010  03 FF 08 00 00 00 00 00 01 20 01 00 00 00 00 00  ......... ......
 0020  00 FF 00 00 00 00 00 00 00 FF 00 00 00 00 00 00  ................
 0030  00 FF 00 00 00 00 00 00 00 FF 00 00 00 00 00 00  ................
-* Fault: The device on port 233 refused the access at Program Address 0x1359, and nothing is installed to deal with it.
+* that bank will not be written
+* bank 00
+* * 8000  26 48        INIA 48
+8002  D1 00        OUTA 00
+8004  26 0A        INIA 0A
+8006  D1 00        OUTA 00
+8008  18 12        SWI 12
+800A  00           ADD
+800B  00           ADD
+800C  00           ADD
+* H
+finished
+* 8000  26 48        INIA 48
+8002  D1 00        OUTA 00
+8004  26 0A        INIA 0A
+8006  D1 00        OUTA 00
+8008  18 12        SWI 12
+800A  00           ADD
+800B  00           ADD
+800C  00           ADD
+* > greet.sbx               210
+hello.sbx               52
+Life.sbx                1411
+Snake.sbx               2175
+Keys.sbx                663
+Say.sbx                 155
+Break.sbx               128
+notes.txt               21
+8 files
+> halted
 Execution halted.
-[exit 1]
+[exit 0]

Tests/expected/cosmosRun.out

@@ -6,8 +6,9 @@ Life.sbx                1411
 Snake.sbx               2175
 Keys.sbx                663
 Say.sbx                 155
+Break.sbx               128
 notes.txt               21
-7 files
+8 files
 > load what?
 > no such file
 > not a program