Congratulations to the participants and winners.
Special BIG THANKS to the organizers and administrators of this contest. 💐🏵🌷🌻🌹
I'm really proud to see how this community has grown and raised in quality.

do ^ADMIN  indicates that you run a classic straight ObjectScript program.
while WRITE just has 1 direction to act  READ is bi-directional.
READ can send some text as prompt and waits for reply.
The only bi-directinal device I know of are network connections as TCP, UDP, TRM,FTP,..
The common feature is : they communicate out of your IRIS instance.

Inside IRIS  you may do a redirection e.g to some TCP port like |TCP|7000
but then this port is blocked. No other process can touch |TCP|7000.
So you need an external port wrapper to some other port. e.g. |TCP|7100

Then you can handle this bi-directional communication either by sequence
or you have a list of prompts and the expected replies or similar. 

The sequence of operation could then be:

• have a STARTER that runs in background
  • initiate the external wrapper 
  • run do ^ADMIN
• start the FOREGROUND 
  • connect to external wrapper
  • send prompts to terminal
  • get replies from external file
  • send it back to port
  • which forwards it to  ^ADMIN hanging in background

 The most tricky point is to handle situations where the communication
if it is not just 1 Prompt :=> 1 Answer  but
multiple Prompts or WRITEs  :=>1 Answer or 1 Prompt :=> multiple Answers.

So I'd suggest instead of an IRIS internal solution rather look for an
external Terminal program to consume and apply your answer script.  
 

Never tried it for long time , but $system.CSP.Shell() might be a starting point
$system.CSP.*  seems to have some more useful methods.

I followed this rules with (1,1) as base
Starting any other point than (1,1) simply shortens the spiral.
now I reached 259

I really dislike the result as it is composed so unfriendly
just to save same bytes that nobody asked for.

I see a general problem in interpretation of the "spiral" 
so I took some drawing for aquadratíc and a rectangular matrix. 

1. depending on the starting point you have to take a pre-designed direction
2. if you hit the diagonal you have to turn right
3. you have to invalidate the row/column you just were on
4. proceeding to invalid points is not allowed.
5. start a the central point is an immediate termination as it has no direction to proceed

The diagonal came to my mind thinking how to NOT increase the imaginative radius of the spiral.
The related subscripts for the diagonale points of an n*m are found as (-n/2+x,-m/2+y) 
The pink subscripts are obviously (n/2,m/2) and might be just virtual.   

As subscripts start with 1 and first  piece position  is also 1
some more adjustment of coordinates is required

I haven't written any useful line yet.

DC search; Improve selectivity of Articles and Questions by using TAGS
https://ideas.intersystems.com/ideas/DPI-I-630

Very elegant !👍

Just at a  2nd view also N=3 has that problem.
StarMiddleTop   (1,2) has the same Problem as MiddleRight (2,3)
Not all characters of the matrix show up in the result.
it shows DEFGHABI but  DEFGHABC looks similar correct according to published rules
Is this expected behavior? 

2cents more

The clockwise logic is simple for a  3*3 matrix
though starting with 4*4  there is some rule missing on how the handle a dead end
Starting at a corner (1,1) or similar is trivial. 
BUT:  starting at any other point may create a rathole or miss some boxes 

        Set matrix($Increment(matrix)) = "C,O,D,E"
        Set matrix($Increment(matrix)) = "U,C,H,G"
        Set matrix($Increment(matrix)) = "M,U,F,O"
        Set matrix($Increment(matrix)) = "S,I,F,L"

Start (1,1) is in the example but
Start (1,2) runs ODEGOLFISMU what is the next to (2,1) ?  (1,1)  or (2,2) or ??
worse with Start(2,2) already the first according to description could be
up (1,2) or right (2,3) or left (2,1)  leaving dead ends clockwise.
And this is only with N=4  larger grids may create multiple lost cells.
Clockwise spiral is just not detailed enough for a UNIQUE result to collect ALL cells
A rule how to handle / skip already consumed cells might improve.
Just as I type a non straight spiral solution to (2,2) consuming the full matrix
might be CUISMUCODEGOLFFH
 I fail to imagine grids >5*5
  

The ERROR you see happens when you try to store your object
Check the possible index collission before any attempt to Save the object.

set exists=obj.MyIndexExists(Prop1,Prop2)

Now you may handle the critical situation according to your needs
 

2 options:

set mylist = ""
for i = 1:1:5 {
    set item = "item"_i
    set mylist = mylist_$ListBuild(item)
}
zw mylist

kill mylist
for i = 1:1:5 set $li(mylist,i)="item"_i
zw mylist

Just as you did with Studio

see docs: https://docs.intersystems.com/ens201813/csp/documatic/%25CSP.Documatic.cls?LIBRARY=%25SYS&CLASSNAME=%25CSP.Response#ContentLength
• property ContentLength as %String;

Sets the Content-Length header. Since the HTTP headers are sent after the OnPreHTTP() method is complete, setting it after this has no effect.

As a first step I would search Journals to find the Globals affected
if they are not in IRISTEMP/CACHETEMP or PPG of if Journal is switched off.

In order to separate routine calls (abc^myroutine) from real ^globals

Though journal just shows Process Ids, no routine names.

Great idea.
Though it requires to run the whole application repeatedly.
Eventually need to fix transactions broken by <PROTECT>