diff --git a/tests/engine/gate_meta_coverage.lua b/tests/engine/gate_meta_coverage.lua
index 0646247d..2c29d47c 100644
--- a/tests/engine/gate_meta_coverage.lua
+++ b/tests/engine/gate_meta_coverage.lua
@@ -63,13 +63,17 @@ end
 -- engine tier, the SDK cases, and any tests a shipped mod carries
 local function testCorpus()
   local files, bodies = {}, {}
-  local pipe = io.popen(
-    "ls tests/*.lua tests/engine/*.lua tests/modkit/cases/*.lua mods/*/tests/*.lua 2>/dev/null")
-  if pipe then
-    for line in pipe:lines() do
-      if line ~= "" then files[#files + 1] = line end
+  local FsIo = require("tests.fs_io")
+  local function addLuaFrom(dir)
+    for _, name in ipairs(FsIo.listDir(dir)) do
+      if name:match("%.lua$") then files[#files + 1] = dir .. "/" .. name end
     end
-    pipe:close()
+  end
+  addLuaFrom("tests")
+  addLuaFrom("tests/engine")
+  addLuaFrom("tests/modkit/cases")
+  for _, mod in ipairs(FsIo.listDir("mods")) do
+    if not mod:find(".", 1, true) then addLuaFrom("mods/" .. mod .. "/tests") end
   end
   for _, path in ipairs(files) do
     bodies[path] = slurp(path) or ""
diff --git a/tests/fs_io.lua b/tests/fs_io.lua
index 6a1d892e..701189d2 100644
--- a/tests/fs_io.lua
+++ b/tests/fs_io.lua
@@ -15,6 +15,71 @@ local function quote(path)
   return "'" .. tostring(path):gsub("'", "'\\''") .. "'"
 end
 
+-- The suites also run on Windows checkouts, where cmd has no ls/find/test.
+-- These probes pick the spelling the host shell understands; anything that
+-- listed a directory through a bare Unix command silently returned nothing
+-- there, and a tier built on an empty listing passes vacuously.
+FsIo.isWindows = package.config:sub(1, 1) == "\\"
+
+local function shellLines(cmd)
+  local lines = {}
+  local pipe = io.popen(cmd)
+  if not pipe then return lines end
+  for line in pipe:lines() do
+    if line ~= "" then lines[#lines + 1] = line end
+  end
+  pipe:close()
+  return lines
+end
+
+-- names directly inside path (files and directories mixed, like ls -1)
+function FsIo.listDir(path)
+  local cmd
+  if FsIo.isWindows then
+    cmd = 'dir /b "' .. tostring(path) .. '" 2>nul'
+  else
+    cmd = "ls -1 " .. quote(path) .. " 2>/dev/null"
+  end
+  local items = shellLines(cmd)
+  table.sort(items)
+  return items
+end
+
+-- every *.lua under dir, recursively, as forward-slash paths
+function FsIo.luaFilesUnder(dir)
+  local cmd
+  if FsIo.isWindows then
+    cmd = 'dir /b /s "' .. tostring(dir) .. '\\*.lua" 2>nul'
+  else
+    -- -L follows symlinks: a checkout that symlinks src/ (worktrees, the
+    -- ROM-free CI probe) would otherwise scan nothing and hand every gate
+    -- an empty catalog to pass vacuously against
+    cmd = "find -L " .. quote(dir) .. " -name '*.lua' -type f 2>/dev/null"
+  end
+  local files = {}
+  for _, line in ipairs(shellLines(cmd)) do
+    files[#files + 1] = (line:gsub("\\", "/"))
+  end
+  table.sort(files)
+  return files
+end
+
+-- existence probe that never shells out on Windows: directories do not
+-- open() there at all, and rename-self succeeds for anything that exists
+function FsIo.isDir(path)
+  local handle = io.open(path, "rb")
+  if handle then
+    local probe = handle:read(1)
+    handle:close()
+    if probe ~= nil then return false end
+    if FsIo.isWindows then return false end -- opened but empty: a file
+  elseif FsIo.isWindows then
+    return os.rename(path, path) == true
+  end
+  local ok = os.execute("test -d " .. quote(path))
+  return ok == true or ok == 0
+end
+
 function FsIo.new(rootDir)
   local base = rootDir or "."
 
@@ -50,8 +115,7 @@ function FsIo.new(rootDir)
       -- a directory opens on some libc builds but reads nothing
       if probe ~= nil then return { type = "file" } end
     end
-    local ok = os.execute("test -d " .. quote(abs(path)))
-    if ok == true or ok == 0 then return { type = "directory" } end
+    if FsIo.isDir(abs(path)) then return { type = "directory" } end
     if handle then return { type = "file" } end
     return nil
   end
@@ -61,15 +125,7 @@ function FsIo.new(rootDir)
   end
 
   function fs.getDirectoryItems(path)
-    local items = {}
-    local pipe = io.popen("ls -1 " .. quote(abs(path)) .. " 2>/dev/null")
-    if not pipe then return items end
-    for line in pipe:lines() do
-      if line ~= "" then items[#items + 1] = line end
-    end
-    pipe:close()
-    table.sort(items)
-    return items
+    return FsIo.listDir(abs(path))
   end
 
   fs.root = base
diff --git a/tests/modkit/catalog.lua b/tests/modkit/catalog.lua
index 5963ae4d..5fce4fd9 100644
--- a/tests/modkit/catalog.lua
+++ b/tests/modkit/catalog.lua
@@ -10,22 +10,12 @@
 -- call site exists.
 
 local Schemas = require("src.mods.Schemas")
+local FsIo = require("tests.fs_io")
 
 local Catalog = {}
 
 local function luaFilesUnder(dir)
-  local files = {}
-  -- -L follows symlinks: a checkout that symlinks src/ (worktrees, the
-  -- ROM-free CI probe) would otherwise scan nothing and hand every gate an
-  -- empty catalog to pass vacuously against
-  local pipe = io.popen("find -L " .. dir .. " -name '*.lua' -type f 2>/dev/null")
-  if not pipe then return files end
-  for line in pipe:lines() do
-    if line ~= "" then files[#files + 1] = line end
-  end
-  pipe:close()
-  table.sort(files)
-  return files
+  return FsIo.luaFilesUnder(dir)
 end
 
 local function scan(dirs, patterns)
diff --git a/tests/run_modkit.lua b/tests/run_modkit.lua
index b1814ac2..0849f3ce 100644
--- a/tests/run_modkit.lua
+++ b/tests/run_modkit.lua
@@ -11,12 +11,12 @@ local dirs = { "tests/modkit/cases" }
 
 -- mods ship their own tests (21-testing-and-ci "how mods ship their own
 -- tests"); pick up every mods/<id>/tests directory that exists
-local pipe = io.popen("ls -d mods/*/tests 2>/dev/null")
-if pipe then
-  for line in pipe:lines() do
-    if line ~= "" then dirs[#dirs + 1] = line end
+local FsIo = require("tests.fs_io")
+for _, name in ipairs(FsIo.listDir("mods")) do
+  if not name:find(".", 1, true) then
+    local dir = "mods/" .. name .. "/tests"
+    if FsIo.isDir(dir) then dirs[#dirs + 1] = dir end
   end
-  pipe:close()
 end
 
 Runner.main(dirs, "modkit")
diff --git a/tests/tier_runner.lua b/tests/tier_runner.lua
index 02ea8b0f..724ee7eb 100644
--- a/tests/tier_runner.lua
+++ b/tests/tier_runner.lua
@@ -15,6 +15,8 @@
 
 local Runner = {}
 
+local FsIo = require("tests.fs_io")
+
 local function interpreter()
   -- arg[-1] is how the suite was invoked (luajit here, lua5.4 elsewhere)
   return (arg and arg[-1]) or "luajit"
@@ -22,17 +24,13 @@ end
 
 function Runner.suites(dir)
   local files = {}
-  local pipe = io.popen(("ls -1 '%s'/*.lua 2>/dev/null"):format(dir))
-  if not pipe then return files end
-  for line in pipe:lines() do
-    local name = line:match("[^/]+$")
+  for _, name in ipairs(FsIo.listDir(dir)) do
     -- "_" prefixes helpers; facts.lua is the tier's pinned-value table
     -- (a content_<mod>/facts.lua is data the suites read, not a suite)
-    if name and name:sub(1, 1) ~= "_" and name ~= "facts.lua" then
-      files[#files + 1] = line
+    if name:match("%.lua$") and name:sub(1, 1) ~= "_" and name ~= "facts.lua" then
+      files[#files + 1] = dir .. "/" .. name
     end
   end
-  pipe:close()
   table.sort(files)
   return files
 end