diff --git a/lib/maker/make-pathway-tocs.lua b/lib/maker/make-pathway-tocs.lua
index 3bbd0be4d45..440a8e15667 100755
--- a/lib/maker/make-pathway-tocs.lua
+++ b/lib/maker/make-pathway-tocs.lua
@@ -23,6 +23,13 @@ for _,course in ipairs(all_courses) do
   local this_course_lessons_file = course_dir .. '.cached/.workbook-lessons.rkt.kp'
   if not file_exists_p(this_course_lessons_file) then goto continue end
   local lesson_units = sread_file(this_course_lessons_file)
+  -- An empty or malformed .kp makes sread_file return a non-table (false on
+  -- empty/exhausted input). Skip the course rather than indexing into it.
+  if type(lesson_units) ~= 'table' then
+    io.stderr:write('WARNING: skipping pathway-toc for ' .. course ..
+      ' -- empty/unparseable ' .. this_course_lessons_file .. '\n')
+    goto continue
+  end
   o:write('  \"' .. course .. '\": [\n')
   for _,lunit in ipairs(lesson_units) do
     local unit_name = lunit[1]
diff --git a/lib/maker/make-workbook-lessons-list.lua b/lib/maker/make-workbook-lessons-list.lua
index dc8607c3d51..b69a35dd659 100755
--- a/lib/maker/make-workbook-lessons-list.lua
+++ b/lib/maker/make-workbook-lessons-list.lua
@@ -1,16 +1,13 @@
 #! /usr/bin/env lua
 
--- last modified 2026-03-10
+-- last modified 2026-06-15
 
 local inf, outf, pl = ...
 
-local i = io.open(inf, 'r')
-local o = io.open(outf, 'w')
-
 local current_unit = 'NO_UNIT'
 local current_unit_lessons = {}
 
-local function write_unit()
+local function write_unit(o)
   if #current_unit_lessons > 0 then
     o:write('( "' .. current_unit .. '"\n')
     for _,y in ipairs(current_unit_lessons) do
@@ -26,28 +23,42 @@ if pl ~= 'pyret' and pl ~= 'none' then
   proglang = '-' .. pl
 end
 
-o:write('(\n')
-
-for x0 in i:lines() do
-  local x = x0
-  x = x:gsub('^%s+', '')
-  x = x:gsub(';.*', '')
-  x = x:gsub('%s+$', '')
-  if x == '' then goto continue end
-  if x:find('^%[') then
-    x = x:gsub('%[%s*(.-)%s*%]', '%1')
-    write_unit()
-    current_unit = x
-    current_unit_lessons = {}
-  else
-    x = x .. proglang
-    table.insert(current_unit_lessons, x)
+local function get_all_lines(inf)
+  local the_lines = {}
+  for L in io.lines(inf) do
+    table.insert(the_lines, L)
   end
-  ::continue::
+  return the_lines
 end
-write_unit()
 
-o:write(')\n')
+local function write_all_units(inf, outf)
+  local the_lines = get_all_lines(inf)
+  local o = io.open(outf, 'w')
+
+  o:write('(\n')
+
+  for _,x0 in ipairs(the_lines) do
+    local x = x0
+    x = x:gsub('^%s+', '')
+    x = x:gsub(';.*', '')
+    x = x:gsub('%s+$', '')
+    if x == '' then goto continue end
+    if x:find('^%[') then
+      x = x:gsub('%[%s*(.-)%s*%]', '%1')
+      write_unit(o)
+      current_unit = x
+      current_unit_lessons = {}
+    else
+      x = x .. proglang
+      table.insert(current_unit_lessons, x)
+    end
+    ::continue::
+  end
+  write_unit(o)
+
+  o:write(')\n')
+
+  o:close()
+end
 
-i:close()
-o:close()
+write_all_units(inf, outf)
diff --git a/lib/maker/massage-course.sh b/lib/maker/massage-course.sh
index c0c22fb4780..1097b4bc809 100755
--- a/lib/maker/massage-course.sh
+++ b/lib/maker/massage-course.sh
@@ -72,12 +72,22 @@ for pl in $proglangs; do
     fi
   done
 
+  # Publish .workbook-lessons.rkt.kp atomically. make-workbook-lessons-list.lua
+  # opens its output with 'w' (truncates to 0 immediately), so a crash or
+  # interrupt would leave a 0-byte file that a later build's reader chokes on.
+  # Write a temp and mv it into place only on success; never leave it empty.
+  kp=.cached/.workbook-lessons.rkt.kp
   if test ! -f lesson-order.txt; then
     echo WARNING: No lesson-order.txt in pathway $targetpathway
     touch lesson-order.txt
-    touch .cached/.workbook-lessons.rkt.kp
+    printf '()\n' > "$kp"        # valid empty s-expression, not a 0-byte file
   else
-    $TOPDIR/${MAKE_DIR}make-workbook-lessons-list.lua lesson-order.txt .cached/.workbook-lessons.rkt.kp $pl
+    if $TOPDIR/${MAKE_DIR}make-workbook-lessons-list.lua lesson-order.txt "$kp.tmp" $pl; then
+      mv -f "$kp.tmp" "$kp"
+    else
+      echo "ERROR: make-workbook-lessons-list failed for $targetpathway; keeping previous $kp" >&2
+      rm -f "$kp.tmp"
+    fi
   fi
 
   cd ..
diff --git a/lib/maker/sread.lua b/lib/maker/sread.lua
index ae12a62e576..21e7cf7c98f 100644
--- a/lib/maker/sread.lua
+++ b/lib/maker/sread.lua
@@ -9,7 +9,7 @@
 local function sread_line(i)
   while true do
     local c = i:read(1)
-    if c == '\r' or c == '\n' then
+    if c == nil or c == '\r' or c == '\n' then  -- nil == EOF
       break
     end
   end
@@ -18,7 +18,9 @@ end
 local function sread_block_comment(i)
   while true do
     local c = i:read(1)
-    if c == '|' then
+    if c == nil then  -- EOF inside an unterminated block comment
+      break
+    elseif c == '|' then
       c = i:read(1)
       if c == '#' then
         break
@@ -66,8 +68,8 @@ local function sread_atom(i)
       in_escape_p = true
       i:read(1)
       table.insert(result, c)
-    elseif c == ' ' or c == '\t' or c == '\n' or c == '\r' or c == '(' or c == '[' or c == ')' or c == ']' or c == ';' then
-      break
+    elseif c == nil or c == ' ' or c == '\t' or c == '\n' or c == '\r' or c == '(' or c == '[' or c == ')' or c == ']' or c == ';' then
+      break  -- nil == EOF terminates the atom
     else
       i:read(1)
       table.insert(result, c)
@@ -97,7 +99,9 @@ local function sread_string(i)
   local in_escape_p = false
   while true do
     local c = i:read(1)
-    if in_escape_p then
+    if c == nil then  -- EOF inside an unterminated string
+      break
+    elseif in_escape_p then
       in_escape_p = false
       table.insert(result, c)
     elseif c == '\\' then
@@ -116,7 +120,9 @@ function sread(i)
   sread_ignorespaces(i)
   local c = buf_peek_char(i)
   local result = false
-  if c == '(' or c == '[' then
+  if c == nil then  -- EOF: no s-expression to read (empty/exhausted input)
+    result = false
+  elseif c == '(' or c == '[' then
     i:read(1)
     result = sread_list(i)
   elseif c == ')' or c == ']' then