What to make of $!:tt puzzle.!txt$?

Puzzling Stack Exchange:

Don’t even ask where I found
the old printout, below, of an uncommented computer program.
As I am a leading-edge software solutionaut
hone-tuned for elegantly annotated exoticode,
reconnoitering this printout is beneath my paygrade.
All I’ve bothered to notice is that some drone
meant this program to spin out something called "puzzle.txt".
I need for you to spec the deets for me.

  Assuming that puzzle.txt is a puzzle, what kind?
How is this program supposed to produce it?

  Know that I am particularly impatient to be debriefed on
the identities of the 7 characters besmirched on line 200.

  200 w$(1,0) = ??????? [7 smudged characters]

  It would be really great if you could also
dummy up
a possible printout of puzzle.txt by noon, okay?.

 10  rows = 8 : columns = 8
 20  dim n(rows,columns), f$(rows,columns), w$(rows,columns)
 30  for r = 0 to rows : for c = 0 to columns
 40      n(r,c) = 0
 50      f$(r,c) = "_"
 60      if r=0 then w$(r,c) = "_" else w$(r,c) = "|"
 70  next c : next r
 80  w$(0,columns) = " " : w$(rows,columns) = "_"
 90  d = INT(4*RND) : r = 1+INT(rows*RND) : c = 1+INT(columns*RND)
100  n(r,c) = 1
110  unvisited = rows*columns - 1
120  while unvisited > 0
130      d = INT( d + 3.6 + 2.4*RND ) mod 4
140      if d=3 and c < columns then:  c = c+1 : if n(r,c)=0 then w&dollar;(r,c-1) = "_"
150      if d=1 and c > 1       then:  c = c-1 : if n(r,c)=0 then w&dollar;(r,c)   = "_"
160      if d=0 and r > 1       then:  r = r-1 : if n(r,c)=0 then f&dollar;(r,c)   = " "
170      if d=2 and r < rows    then:  r = r+1 : if n(r,c)=0 then f&dollar;(r-1,c) = " "
180      if n(r,c)=0 then:  n(r,c) = 1 : unvisited = unvisited-1
190  wend
200  w&dollar;(1,0) = ???????  [7 smudged characters]
210  for r = 1 to rows-1 : for c = 1 to columns-1
220      if f&dollar;(r,c)=" " or f&dollar;(r,c+1)=" " then:  if w&dollar;(r,c)="_" then w&dollar;(r,c) = " "
230  next c : next r
240  open "o", #1, "puzzle.txt"
250  for r = 0 to rows : for c = 0 to columns
260          if c > 0 then print #1, f&dollar;(r,c);
270          print #1, w&dollar;(r,c);
280      next c : print #1,""
290  next r : close #1 : end

(Yeah yeah, no this is not
an actual corporate-speak demand for information,
but the challenge is to answer as if it were.
The no-computers tag means that
the real old program should not be run
in order to figure it out or to make the sample puzzle.txt.)

puzzle-identification