Try a more robust way of parsing out the linesep

etc/bytedump.sh

@@ -7,33 +7,47 @@ else
   DEBUG="False"
 fi
 
+needle1="NEEDLE1"
+needle2="COQTOP_CRAP_ENDS_HERE"
+
 {
 coqtop -q -quiet $COQFLAGS 2>/dev/null << EOF
 Require bedrock2.PrintListByte ${1%.*}.
 Local Set Printing Width 2147483647.
 Goal True.
-  idtac "COQTOP_CRAP_ENDS_HERE".
+  idtac "${needle1}".
+  idtac "${needle2}".
   PrintListByte.print_list_byte ${1}.
 Abort.
 EOF
 } | python3 -c '
 import os, sys
-needle = b"COQTOP_CRAP_ENDS_HERE"
+needle1 = b"'"${needle1}"'"
+needle2 = b"'"${needle2}"'"
 # waiting_on_coqbug_15373 = True
 debug = '"$DEBUG"'
+full = b""
+b = b""
+# first read to needle1
+while not b.endswith(needle1):
+	r = os.read(0, 1)
+	if not r:
+		if debug: full += b
+		if debug: print(f"Error: waiting for {needle1!r} when reading {b!r}", file=sys.stderr)
+		sys.exit(2)
+	b += r
+if debug: full += b
+# parse line separator by reading to needle2
 b = b""
-# first read to needle
-while not b.endswith(needle):
+while not b.endswith(needle2):
 	r = os.read(0, 1)
 	if not r:
-		print(f"Error: waiting for {needle!r} when reading {b!r}", file=sys.stderr)
+		if debug: full += b
+		if debug: print(f"Error: waiting for {needle2!r} when reading {full!r}", file=sys.stderr)
 		sys.exit(2)
 	b += r
-# parse line separator as the 1 or two characters before the needle which are either \r or \n
-sep = b[-(len(needle)-2):-len(needle)]
-if sep[1] not in b"\r\n":
-	print(f"Error: sep ({sep!r}) does not end with \\r nor \\n when reading {b!r}", file=sys.stderr)
-	sys.exit(3)
+if debug: full += b
+sep = b[:-len(needle2)]
 # skip sep
 r = os.read(0, len(sep))
 if debug: full = b + r