diff --git a/src/lua/module_loader.cpp b/src/lua/module_loader.cpp
index ce30d00..9ca91df 100644
--- a/src/lua/module_loader.cpp
+++ b/src/lua/module_loader.cpp
@@ -6,6 +6,25 @@
 #include "bindings.h"
 #include "lua_app.h"
 
+// Streamed rather than slurped: holding a whole module as one String needs that many bytes
+// contiguous, and once WiFi is up the largest free block is around 40KB even though far
+// more than that is free. Lua only ever wants the next few bytes.
+namespace {
+struct ChunkReader {
+  File file;
+  char buf[512];
+};
+
+const char* readChunk(lua_State*, void* ud, size_t* size) {
+  ChunkReader* reader = static_cast<ChunkReader*>(ud);
+  int read = reader->file.read((uint8_t*)reader->buf, sizeof(reader->buf));
+  *size = read > 0 ? (size_t)read : 0;
+  return read > 0 ? reader->buf : nullptr;
+}
+}  // namespace
+
+// Whole file in one String, for callers that want the bytes themselves. Scripts go through
+// loadScript(), which never materializes the file.
 bool readScript(const char* path, String& out) {
   // Probe first: a missed SD.open logs a VFS error, and the searcher misses by design.
   if (!SD.exists(path)) return false;
@@ -14,19 +33,31 @@ bool readScript(const char* path, String& out) {
     if (file) file.close();
     return false;
   }
+  // readString() reports an allocation failure by silently returning a partial read, so the
+  // size is verified rather than trusted: a truncated script is a syntax error at a random
+  // offset, which says nothing about the real cause.
+  size_t size = file.size();
   out = file.readString();
   file.close();
+  if (out.length() != size) {
+    Serial.printf("[lua] %s: short read, %u of %u bytes\n", path, out.length(), (unsigned)size);
+    return false;
+  }
   return true;
 }
 
 int loadScript(lua_State* L, const char* path) {
-  String source;
-  if (!readScript(path, source)) {
+  ChunkReader reader;
+  if (SD.exists(path)) reader.file = SD.open(path);
+  if (!reader.file || reader.file.isDirectory()) {
+    if (reader.file) reader.file.close();
     lua_pushfstring(L, "cannot open %s", path);
     return LUA_ERRFILE;
   }
   String chunkname = String("@") + path;
-  return luaL_loadbuffer(L, source.c_str(), source.length(), chunkname.c_str());
+  int status = lua_load(L, readChunk, &reader, chunkname.c_str(), "t");
+  reader.file.close();
+  return status;
 }
 
 static int l_loadfile(lua_State* L) {
@@ -64,10 +95,8 @@ static int l_searcher(lua_State* L) {
     if (candidate.length() == 0) continue;
     candidate.replace("?", name);
 
-    String source;
-    if (readScript(candidate.c_str(), source)) {
-      String chunkname = String("@") + candidate;
-      if (luaL_loadbuffer(L, source.c_str(), source.length(), chunkname.c_str()) != LUA_OK) {
+    if (SD.exists(candidate.c_str())) {
+      if (loadScript(L, candidate.c_str()) != LUA_OK) {
         return luaL_error(L, "error loading module '%s' from '%s':\n\t%s",
                           luaL_checkstring(L, 1), candidate.c_str(), lua_tostring(L, -1));
       }
diff --git a/src/main.cpp b/src/main.cpp
index 06662b8..e9b36fa 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -50,7 +50,7 @@ void startApp(const String& path) {
   // Full panel until the app's own status bar module reports its height in load().
   tft.setRotation(settings.rotationIndex());  // apps may have rotated the frame
   tft.resetViewport();  // load() re-clips once the new app's bar reports its height
-  Serial.printf("launching %s\n", path.c_str());
+  Serial.printf("launching %s free=%u largest=%u\n", path.c_str(), ESP.getFreeHeap(), ESP.getMaxAllocHeap());
   if (app.load(path.c_str(), path == HOME)) return;
   if (path == HOME) fallbackScreen("home failed to start");
 }