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/makedisks.sh

@@ -177,6 +177,25 @@ awk 'BEGIN { for (i = 0; i < 30; i++) printf "line %02d: ABCDEFGHIJKLMNOPQRSTUVW
     "$ROOT/Programs/CosmOS/Apps/More.asm" -o "$WORK/More.sbx" >/dev/null
 "$TOOL" put "$DISKS/type.img" "$WORK/More.sbx" >/dev/null
 
+# A disk for invoking a program by typing its name. Four files, each there to say one
+# thing about how a typed word turns into a file name.
+#
+# dir.sbx is a working program under the name of a built-in command, which is the only way
+# to check that the built-ins really are tried first. If the search ever moved ahead of the
+# dispatch chain, this disk would start answering "dir" with a program.
+#
+# notes.sbx is text under a program's name, so that a file that IS found and IS NOT a
+# program can be told apart from a word that names nothing. notes.txt is the same text
+# under its own name, which no typed word can reach: "notes.txt" looks for notes.txt.sbx.
+"$TOOL" format "$DISKS/invoke.img" 64 2 >/dev/null
+"$ROOT/Assembler" -I "$ROOT/Programs/CosmOS/Source" \
+    "$ROOT/Programs/CosmOS/Apps/Say.asm" -o "$WORK/Say.sbx" >/dev/null
+"$TOOL" put "$DISKS/invoke.img" "$WORK/Say.sbx" >/dev/null
+"$TOOL" put "$DISKS/invoke.img" "$WORK/Say.sbx" dir.sbx >/dev/null
+printf 'this is not a program' > notes.txt
+"$TOOL" put "$DISKS/invoke.img" notes.txt >/dev/null
+"$TOOL" put "$DISKS/invoke.img" notes.txt notes.sbx >/dev/null
+
 # A disk for the assembler that runs on the machine. It holds a source file and the two
 # programs that check the front end - the reader on its own and the tokenizer on its own -
 # because a fault in either of those would otherwise turn up much later as a mysterious