A program can say how it went

SWI osExit takes a status in A, and the shell keeps it. Fifty eight exits
across twenty three programs now say deliberately whether they worked: 25
did what they were asked, 24 did not, 9 were asked wrongly. Compare is the
exception and says so - one there means the files differ, which is a result
rather than a failure, the way diff has always had it.

IN A RATHER THAN Q, which is not a departure from the rule that a service
answers in Q. This one takes an ARGUMENT, the way osPrintNumber takes A and
B, and it never returns to answer anything. A is free precisely because a
return would have put it back - and Q is the ALU's output, so a small
number costs four instructions there against one in A.

The shell does not print it. A program that failed has already said so in
words and a number beside that is noise, so osLastStatus hands it back and
Status is the program that shows it. That indirection is the point: the
number exists for the thing that cannot read words.

MARKING THE EXITS FOUND A DEFECT ON THE FIRST RUN. Type and More printed
why they had failed and then fell through into the success exit, reporting
that all was well. Nobody had noticed, because while the only reader was a
person, the person could see both the complaint and the claim.

Two smaller things. Snake sets the console to line mode and then exits with
zero, and the linter flagged the second RSTA as redundant - an exit status
and a console mode, equal by accident, which is the class that must never
be collapsed. And the README still taught answering by writing into the
frame, three months of habit that SRET replaced yesterday; that section is
gone and the one describing SRET stands in its place.

Programs/CosmOS/Source/cosmos.asm

@@ -2242,6 +2242,18 @@ handlePrintNumber:
 ;
 ; Which is exactly why this cannot RETI. Its return address is on the Stack it just walked
 ; away from, so it branches to the prompt instead.
+; What the last program made of what it was asked to do. Kept rather than shown: a program
+; that failed has already said so in words, and a number beside that would be noise. It is
+; here for the thing that cannot read words - whatever comes to run programs in sequence and
+; has to decide whether to run the next one.
+handleLastStatus:
+  SETD.2 LastStatus
+  LDA.2
+  RSTB
+  CCF
+  ADD                       ; A is the answer, so Q becomes it.
+  SRET
+
 ; ---- How the last start went, and settling it ----
 ;
 ; The answer goes in Q by writing into this handler's own frame, which is how every service
@@ -2292,6 +2304,17 @@ bootSettleNo:
   SRET
 
 handleExit:
+  ; ---- What the program made of it ----
+  ;
+  ; A, before anything below disturbs it. IN A RATHER THAN Q, and that is not a departure
+  ; from the rule that a service answers in Q: this one takes an argument, the way
+  ; osPrintNumber takes A and B, and it never returns to answer anything. The register a
+  ; subroutine cannot hand anything back in is exactly the one that is free here - and Q is
+  ; the ALU's output, so setting it to a small number costs four instructions where A costs
+  ; one.
+  SETD.1 LastStatus
+  STA.1
+
   SETD.1 SystemStack
   LDD.0.1
   MVDS.0
@@ -3417,6 +3440,10 @@ Banner:
 "CosmOS"
 PromptText:
 "> "
+; Nothing has run yet, so nothing has failed yet.
+LastStatus:
+  0x00
+
 OnFallback:
 "this is the fallback: what boot.cfg asks for did not start
 "
@@ -3913,6 +3940,7 @@ CommandLine:
   osFileFetch    handleFileFetch
   osPrintNumber  handlePrintNumber
   osBreak        handleBreak
+  osLastStatus   handleLastStatus
   osBootState    handleBootState
   osBootSettle   handleBootSettle
   Device 0x20    diskDone

Programs/CosmOS/Source/services.asm

@@ -153,3 +153,17 @@
 ; about something the loader has no way to check.
   osBootState    0d33
   osBootSettle   0d34
+
+; ---- What a program made of it ----
+;
+; osExit takes a status in A: zero if the program did what it was asked, and a number of
+; its own choosing if it did not. IN A RATHER THAN Q, which is not a departure from the
+; rule that a service answers in Q - this one takes an argument, the way osPrintNumber
+; does, and never returns to answer anything. A is free precisely because a return would
+; have put it back, and Q is the ALU's output, so a small number costs four instructions
+; there and one in A.
+;
+; osLastStatus answers in Q with what the last program exited with. The shell does not
+; print it: a program that failed has already said so in words, and a number beside that
+; would be noise. This is for the thing that cannot read words.
+  osLastStatus   0d35