Tell the person where it hurts

A fault stopped the machine and printed a line to standard error. On a terminal
that is a diagnosis. Behind a window it is a frozen picture and no reason at
all, because the message went somewhere nobody was looking - the machine looked
hung and was not. It had stopped, and said so invisibly.

CosmOS catches all five faults now and says what happened on the screen, with
the address, in red.

A FAULT ENDS THE PROGRAM, NOT THE MACHINE. That is the answer to "carry on or
start again", and it is not a compromise: a bare RETI from most of these meets
the instruction that failed and fails again, so carrying on was never on offer.
But the machine is almost never what is broken. Everything the shell puts back
when a program exits - the Stack, its vectors, the drive, the working directory,
the console, the screen - is exactly what wants putting back after one dies, so
the handler sets a status and joins handleExit. You are back at the prompt, and
the program is recorded as having STOPPED rather than finished, because saying
"finished" under a red fault message would be the shell contradicting itself.

A fault below where programs load is the system's own, and there is nothing to
go back to. That one says so and stops.

THE SCREEN GOES BACK TO A MODE TEXT CAN BE SEEN IN, and that is the part that
matters rather than the part that is prettiest. A program that faulted in bitmap
mode left the console with no text rows, so it draws nothing at all: the message
would be perfectly correct and completely invisible, which is the one thing it
must never be. Two palette entries go back for the same reason, since a program
that wrote its own colours can leave every ink the same as every paper. Only the
two the message needs, so the rest of what the program chose is left alone.

Both halves are checked by looking at the PICTURE, because the serial line was
never where the problem was. Crash blind ruins the palette and drops into bitmap
mode before it faults; without the mode the screen comes back 320 by 200 with
nothing on it, and without the palette it is the right size with the message
present and unreadable. Each break loses the red on its own.

Crash is also a program worth having: it breaks in whichever of the five ways
you name, so a fault screen can be looked at without having written a bug first.

Two things found on the way:

The native assembler keeps its OWN copy of the reserved vector names, so it did
not know NoHandler or NoDevice and built a cosmos.bin that differed from the
host assembler's. Caught by native.sh, which is exactly the drift that test
exists for.

And cosmosMonitor had dead input. It assembles code into 0x8000 and runs it, and
that code faults - which used to kill the machine, so everything after it in the
file had never run. It runs now, and the recording grew by sixty lines of
monitor session that had been unreachable since the day the fault was put there.

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

Tests/manifest

@@ -326,6 +326,20 @@ cosmosPressKeys      | CosmOS/Source/cosmos.asm           | run      | -
 # a forty column screen, which is a width nothing else here ever runs at - and the shell
 # reads that width for itself now, every line it edits.
 cosmosNoData         | CosmOS/Source/cosmos.asm           | run      | cosmosNoData.in    | -     | disks/cosmos.img
+# The system catching a fault instead of the machine stopping on one. All four causes, one
+# after another, and a dir at the end: THE POINT IS THE LINE AFTER THE FAULT. Every one of
+# these used to stop the machine dead, and behind a window it looked like a hang because the
+# diagnosis went to a standard error nobody was looking at.
+#
+# The addresses are exact and are the reason the recording is worth having. Note that the
+# missing service reports the address PAST its SWI, where the others report the instruction
+# that failed: those two faults are the only ones where the instruction did dispatch and it
+# was the entry that was empty.
+cosmosFault          | CosmOS/Source/cosmos.asm           | run      | cosmosFault.in     | -     | disks/cosmos.img
+# And a fault in the system's own code, which has nowhere to go back to. Reached through the
+# monitor by jumping into the unwritten space above CosmOS and below where programs load,
+# which is zeroes - so it faults at once and corrupts nothing on the way.
+cosmosFaultSystem    | CosmOS/Source/cosmos.asm           | run      | cosmosFaultSys.in  | -     | disks/cosmos.img
 # The shell editing the line it is being given, which is the whole reason the keys were
 # made to arrive. Every line here is typed wrong and then corrected with a different key, and
 # every one of them comes out as the same command - so the recording says both what the