diff --git a/src/core/fs_storage.mbt b/src/core/fs_storage.mbt
index d6d5148..43cf974 100644
--- a/src/core/fs_storage.mbt
+++ b/src/core/fs_storage.mbt
@@ -76,7 +76,7 @@ extern "js" fn fs_write_string(path : String, content : String) -> Unit =
   #| }
 
 ///|
-extern "js" fn fs_readdir(path : String) -> Array[String] =
+extern "js" fn fs_readdir_ffi(path : String) -> FixedArray[String] =
   #| (path) => {
   #|   try {
   #|     const fs = require("node:fs");
@@ -86,6 +86,10 @@ extern "js" fn fs_readdir(path : String) -> Array[String] =
   #|   }
   #| }
 
+fn fs_readdir(path : String) -> Array[String] {
+  Array::from_fixed_array(fs_readdir_ffi(path))
+}
+
 ///|
 extern "js" fn fs_is_file(path : String) -> Bool =
   #| (path) => {
diff --git a/src/core/git_loader.mbt b/src/core/git_loader.mbt
index c633990..2e25fb0 100644
--- a/src/core/git_loader.mbt
+++ b/src/core/git_loader.mbt
@@ -239,7 +239,7 @@ extern "js" fn node_read_file_safe(path : String) -> Bytes? =
   #| }
 
 ///|
-extern "js" fn node_readdir_safe(path : String) -> Array[String] =
+extern "js" fn node_readdir_safe_ffi(path : String) -> FixedArray[String] =
   #| (path) => {
   #|   try {
   #|     const fs = require("node:fs");
@@ -249,6 +249,10 @@ extern "js" fn node_readdir_safe(path : String) -> Array[String] =
   #|   }
   #| }
 
+fn node_readdir_safe(path : String) -> Array[String] {
+  Array::from_fixed_array(node_readdir_safe_ffi(path))
+}
+
 ///|
 extern "js" fn node_is_dir(path : String) -> Bool =
   #| (path) => {
@@ -268,7 +272,7 @@ extern "js" fn node_is_file(path : String) -> Bool =
   #| }
 
 ///|
-extern "js" fn scan_readdir(path : String) -> Array[String] =
+extern "js" fn scan_readdir_ffi(path : String) -> FixedArray[String] =
   #| (path) => {
   #|   try {
   #|     const fs = require("node:fs");
@@ -278,6 +282,10 @@ extern "js" fn scan_readdir(path : String) -> Array[String] =
   #|   }
   #| }
 
+fn scan_readdir(path : String) -> Array[String] {
+  Array::from_fixed_array(scan_readdir_ffi(path))
+}
+
 ///|
 /// Scan files in a directory recursively, skipping common non-source dirs.
 pub fn scan_files(root : String, limit~ : Int = 200) -> Array[String] {
diff --git a/src/core/idb_git_fs.mbt b/src/core/idb_git_fs.mbt
index 093bf4b..db73afb 100644
--- a/src/core/idb_git_fs.mbt
+++ b/src/core/idb_git_fs.mbt
@@ -65,10 +65,10 @@ extern "js" fn idb_fs_has(prefix : String, key : String) -> Bool =
   #| })()
 
 ///|
-extern "js" fn idb_fs_list(
+extern "js" fn idb_fs_list_ffi(
   prefix : String,
   dir : String,
-) -> Array[String] =
+) -> FixedArray[String] =
   #| (() => {
   #|   return (prefix, dir) => {
   #|     const cache = globalThis.__idb_fs_cache || {};
@@ -84,6 +84,13 @@ extern "js" fn idb_fs_list(
   #|   };
   #| })()
 
+fn idb_fs_list(
+  prefix : String,
+  dir : String,
+) -> Array[String] {
+  Array::from_fixed_array(idb_fs_list_ffi(prefix, dir))
+}
+
 ///|
 extern "js" fn idb_fs_is_dir(prefix : String, path : String) -> Bool =
   #| (() => {
diff --git a/src/core/r2_storage.mbt b/src/core/r2_storage.mbt
index 62375eb..4542220 100644
--- a/src/core/r2_storage.mbt
+++ b/src/core/r2_storage.mbt
@@ -42,7 +42,7 @@ extern "js" fn r2_put(bucket_name : String, key : String, value : String) -> Uni
   #| })()
 
 ///|
-extern "js" fn r2_list(bucket_name : String, prefix : String) -> Array[String] =
+extern "js" fn r2_list_ffi(bucket_name : String, prefix : String) -> FixedArray[String] =
   #| (() => {
   #|   return (bucket_name, prefix) => {
   #|     const cache = globalThis.__r2_cache || {};
@@ -64,6 +64,10 @@ extern "js" fn r2_list(bucket_name : String, prefix : String) -> Array[String] =
   #|   };
   #| })()
 
+fn r2_list(bucket_name : String, prefix : String) -> Array[String] {
+  Array::from_fixed_array(r2_list_ffi(bucket_name, prefix))
+}
+
 ///|
 extern "js" fn r2_has(bucket_name : String, key : String) -> Bool =
   #| (() => {