Start a program by typing its name

A word the shell has no command for is now looked for on the disk as
"<name>.sbx", and if it is there it is loaded and started exactly as load and
run would do it. Whatever followed the word reaches the program through
osArgument by the same route as whatever follows run, so "Say hello there"
and "Type notes.txt" work without either program knowing how it was started.

load and run are unchanged and both stay. load is how the monitor puts an
arbitrary file in front of itself, which typing a name deliberately cannot do:
the extension is added rather than assumed, so "notes.txt" looks for
notes.txt.sbx and a text file is unreachable by name whatever is inside it.

Three things this had to get right:

The built-ins are tried first and always win. The search hangs off the end of
the dispatch chain, so a file called dir.sbx cannot become dir, and the
commands worth trusting when the disk is what you are doubting stay
trustworthy. The invoke disk carries a working dir.sbx so that this is checked
rather than asserted.

A file that is found but is broken says so. "not a program" and "I do not
know" are different answers, and giving the second about a file sitting on the
disk would send somebody looking in the wrong place. loadProgram therefore
hands back a status as well as a message, since only "no file of that name"
can fairly be reported as anything other than a fault.

doLoad became that subroutine rather than being copied. It ends in RET instead
of a jump to the prompt, and each way of failing sets its number and its text
together so a new one cannot leave half of the answer behind.

cosmosBreak moves because Break prints the pointers it was handed and those
are the shell's leftovers, which a CALL now puts back.

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

Tests/expected/cosmosBreak.out

@@ -3,11 +3,11 @@ CosmOS
 > two stops, and what the registers were at each
 break at 200E
 A 11 B 22 Q 00 status 00 
-DP0 1030 DP1 0663 DP2 039C DP3 2000 SP FFFF
+DP0 1030 DP1 06C2 DP2 0000 DP3 2000 SP FFFF
 press a key 
 break at 2023
 A 44 B 55 Q 00 status 00 
-DP0 1000 DP1 0663 DP2 039C DP3 2000 SP FFF5
+DP0 1000 DP1 06C2 DP2 0000 DP3 2000 SP FFF5
 press a key 
 carried on to the end
 finished