Adopted Array(capacity:) for the read wrappers throughout the library to adapt to Swift 6.4.

Tests/PlaydateKit/MockPlaydate.swift

@@ -35,6 +35,9 @@ enum Mock {
     nonisolated(unsafe) static var buttonState: (current: UInt32, pushed: UInt32, released: UInt32) = (0, 0, 0)
     /// The 16 bytes behind the last pattern `LCDColor` seen by a stub.
     nonisolated(unsafe) static var patternBytes: [UInt8] = []
+    /// Caps the bytes a file read returns (0 = end of file, negative =
+    /// error); `nil` fills the whole request.
+    nonisolated(unsafe) static var fileReadLimit: Int32?
     /// Userdata stored per sprite / menu item, as the OS would keep it.
     nonisolated(unsafe) static var spriteUserdata: [OpaquePointer: UnsafeMutableRawPointer] = [:]
     nonisolated(unsafe) static var menuUserdata: [OpaquePointer: UnsafeMutableRawPointer] = [:]
@@ -83,6 +86,7 @@ enum Mock {
         events = []
         buttonState = (0, 0, 0)
         patternBytes = []
+        fileReadLimit = nil
         spriteUserdata = [:]
         menuUserdata = [:]
         menuCallback = nil
@@ -400,9 +404,10 @@ enum Mock {
             return 0
         }
         fileAPI.pointee.read = { _, buffer, length in
-            memset(buffer, 0xAB, Int(length))
             Mock.record("read(\(length))")
-            return Int32(length)
+            let count = min(Int32(length), Mock.fileReadLimit ?? Int32(length))
+            if count > 0 { memset(buffer, 0xAB, Int(count)) }
+            return count
         }
         fileAPI.pointee.write = { _, _, length in
             Mock.record("write(\(length))")

Tests/PlaydateKit/WrapperTests.swift

@@ -345,6 +345,19 @@ struct WrapperTests {
         #expect(Mock.eventCount("close") == 1)
     }
 
+    @Test func fileHandleReadLengthReturnsOnlyTheBytesRead() throws {
+        let handle = try File.Handle(path: "save.dat", mode: [.read, .readData])
+
+        Mock.fileReadLimit = 3
+        #expect(try handle.read(length: 8) == [0xAB, 0xAB, 0xAB])
+
+        Mock.fileReadLimit = 0
+        #expect(try handle.read(length: 8).isEmpty)
+
+        Mock.fileReadLimit = -1
+        #expect(throws: PlaydateError.self) { try handle.read(length: 8) }
+    }
+
     // MARK: JSON
 
     @Test func jsonDecodeBuildsTheValueTree() throws {